11. Fundamentals of Traffic Engineering - Ricardo G. Sigua.pdf

FUNDAMENTALS OF TRAFFIC ENGINEERING Ricardo G. Sigua

The University of the Philippines Press Diliman, Quezon City

THE UNIVERSITY OF THE PHILIPPINES PRESS E. de los Santos St.. UP Campus. Diliman, Quezon City 1101 Tel. No.: 9253243.9264642 /Telefax No.: 9282558 e-mail: [email protected]

(c) 2008 by Ricardo G. Sigua All rights reserved. No copies can be made in pan or in whole without prior written permission from the author and the publisher.

The National Library of the Philippines CIP Data

Recommended entry:

Sigua. Ricardo C. Fundamentals of traffic engineering/ Ricardo — Quezon G. Sigua. — Quezon City: The University of the

Philippines Press e2008. 346 p.: 23 cm.

1. Traffic engineering — Philippines. Philippines. 2. Traffic safety — Philippines. Philippines. 3. Traffic regulations — Philippines. Philippines. 1 Title.

HE365.5P5 388.312'09599 2008 P074000094 ISBN 978-971-542-552-0

Book Design by Zenaida N. F.halan

Printed in the Philippines

CONTENTS PREFACE 1 INTRODUCTION 1.1 Background 1.1.1 Road Transport Network 1.1.2 Public Transportation 1.1.3 Traffic Management 1.1.4 Pedestrian Facilities 1.1.5 Vehicle Registration 1.1.6 Insurance 1.1.7 Driving License 1.1.8 Driver Apprehensions 1.1.9 Driving Schools 1.1.10 Traffic Enforcement 1.1.11 Legislative Framework 1.1

Transportation and Traffic Engineering Practice 1.2.1 Definitions 1.2.2 Traffic Engineering in the Philippines References 2

TRAFFIC MANAGEMENT 2.1 Introduction 2.2

Traffic Regulations 2.2.1 Effective Traffic Regulation 2.2.2 Three Elements of the Road System

2.3

Traffic Control Devices 2.3.1 Four Elementary Requirements of Every Traffic Control Device

2.4

Traffic Signs and Markings 2.4.1 Elements of Design

2.5

International Standard Traffic Signs 2.5.1 Warning Signs 2.5.2 Priority Signs

2.5.3 2.5.4 2.5.5 2.5.6 2.5.7 2.5.8 2.6

Prohibition Signs Obligatory Signs Other Prescription Signs Information Signs Direction Signs Additional Information

Pavement Markings 2.6.1 Functions and Limitations of Pavement Markings 2.6.2 Legal Authority 2.6.3 Standardization 2.6.4 Types of Markings 2.6.5 Materials 2.6.6 Color 2.6.7 Types of Lines 2.6.8 Width of Lines 2.6.9 Messages 2.6.10 Symbols

2.7

Object Markings and Markers 2.7.1 Object Markings 2.7.2 Raised Pavement Markers Problems References 3

TRAFFIC FLOW FUNDAMENTALS 3.1 Introduction 3.2

Types of Flow 3.2.1 Major Traffic Variables 3.2.2 Other Traffic Variables

3.3

Relationship of Flow, Speed, and Density 3.3.1 Observed Relations 3.3.2 Empirical Relations

3.4

Capacity and Level of Service

3.5

hydrodynamic and Kinematic Models of Traffic

3.6

4

Queuing Theory 3.6.1 D/D/1 Queuing 3.6.2 M/D/1 Queuing 3.6.3 M/M/1 Queuing 3.6.4 M/M/N Queuing

3.7 Shock Wave Problems References TRAFFIC STUDIES 4.1 Introduction 4.2

Volume Studies 4.2.1 Types of Volume 4.2.2 Types of Data Collected 4.2.3 Time of Study 4.2.4 Methods 4.2.5 Presentation of Traffic Volumes 4.2.6 AADT and ADT

4.3

Spot Speed Studies 4.3.1 Time of Study 4.3.2 Size of Samples 4.3.3 Methods 4.3.4 Analysis and Presentation of Spot Speeds

4.4

Travel Time and Delay Studies 4.4.1 Methods

Problems References 5

TRAFFIC STUDIES 5.1 Introduction 5.2

Basic Intersection Design Principles

5.3

Intersection Design Elements

5.4

Methods of Control of Intersections

5.4.1 5.4.2 5.4.3 5.4.4 5.4.5

Unsignalized Intersection Roundabout or Rotary U-Turn Slots Signalized Intersection Grade Separation

5.5

Analysis of Unsignalized Intersections 5.5.1 Structure of Major Road Traffic 5.5.2 Critical Gap 5.5.3 Capacity 5.5.4 Passenger Car Equivalents 5.5.5 Reserve Capacity

5.6

Analysis and Design of Roundabouts or Rotondas

5.7

Traffic Signal Control 5.7.1 Types of Signals 5.7.2 Data Requirements for Traffic Signal Setting 5.7.3 Phase 5.7.4 Lost Times 5.7.5 Cycle 5.7.6 Allocation of Green Times 5.7.7 Capacity of Movement or Approach 5.7.8 Estimation of Delay 5.7.9 Timing Diagram 5.7.10 Intersection Degree of Congestion 5.7.11 Critical Movement Analysis 5.7.12 Treatment of Left Turn Traffic 5.7.13 Left Turn Lane Length 5.7.14 Effects of Left Turn Vehicles on Saturation Flow Rate 5.7.15 Coordination of Traffic Signals 5.7.16 Graphical Method of Coordinating Signalized Intersection 5.7.17 Offset


GEOMETRIC DESIGN OF HIGHWAYS 6.1 Introduction

6.2

Design Requirements of Highways 6.2.1 Design Speed 6.2.2 Slight Distances 6.2.3 Minimum Radius of Curvature 6.2.4 Superelevation 6.2.5 Design Volume 6.2.6 Number of Lanes

6.3

Horizontal Alignment 6.3.1 Circular Curve 6.3.2 Compound Curve 6.3.3 Reverse Curve 6.3.4 Broken Back Curve 6.3.5 Easement Curve or Clothoid

6.4

Vertical Alignment 6.4.1 Properties of Parabolic Vertical Curves 6.4.2 Types of Vertical Curves 6.4.3 General Equation of Vertical Curve 6.4.4 Sight Distances at Vertical Curves 6.4.5 Sight Distances at Crest Vertical Curves 6.4.6 Sight Distances at Sag Vertical Curves


ROAD SAFETY AND TRAFFIC ACCIDENT ANALYSIS 7.1 Introduction 7.2

Assessment of Road Safety 7.2.1 Accident per Population 7.2.2 Accident per Registered Vehicles 7.2.3 Accident Definition 7.2.4 Road Accident Reporting 7.2.5 Present Situation 7.2.6 Key Socioeconomic Indicators 7.2.7 Accidents at Intersections 7.2.8 Accident Rates for Intersections 7.2.9 Accident Rates for Road Sections

7.2.10 Accidents by Time of Day 7.3

Identifying Hazardous Locations or Blackspots 7.3.1 Classic Statistical Method 7.3.2 Rate Quality Control Method 7.3.3 Setting Benchmark Method

7.4

Responses to Safety 7.4.1 The Inter-agency Road Safety Committee and the National Road Safety Committee 7.4.2 Agencies and Institutions Involved in Road Safety

7.5

Initiatives on Road Safety 7.5.1 Imposing Motor Vehicle User’s Fee 7.5.2 Motor Vehicle Inspection System 7.5.3 Seat Belt Law 7.5.4 Banning Use of Cellular Phones and Handset Radios 7.5.5 Other Initiatives

7.6

Road Safety Issues 7.6.1 Legislative 7.6.2 Institutional 7.6.3 Technical 7.6.4 Education and Campaigns 7.6.5 Sociocultural

7.7

Cost of Traffic Accidents 7.7.1 Uses of Accident Cost Estimates 7.7.2 Approaches to Estimating Cost of Accidents 7.7.3 Determination of Cost Components 7.7.4 Estimation of Cost Components

7.8

Estimation of Average Cost of Accidents 7.8.1 Estimation of Cost of a Single Fatal Accident 7.8.2 Estimation of Cost of a Single Serious Injury Accident 7.8.3 Estimation of Cost of a Singe Minor Injury Accident 7.8.4 Estimation of Cost of a Single Property-

7.8.5

7.9

Damage-Only Accident Summary of Average Cost of Each Type of Accident

Estimation of National Cost 7.9.1 Data Availability and Quality 7.9.2 Calculation of National Costs


INTRODUCTION TO TRAVEL DEMAND FORECASTING 8.1 Introduction 8.2

The Four-Step Forecasting Model

8.3

The Origin-Destination Table (OD Matrix)

8.4

Methods for Estimating Trip Generation and Attraction 8.4.1 Growth Rate Method 8.4.2 Category Analysis 8.4.3 Regression Analysis

8.5

Trip Distribution 8.5.1 Present Pattern Method 8.5.2 Model Method

8.6

Modal Split 8.6.1 The Generalized Cost 8.6.2 Disaggregate Choice Model

8.7

Route Assignment 8.7.1 The Shortest Path 8.7.2 Network Assignment


INTRODUCTION TO INTELLIGENT TRANSPORTATION SYSTEM 9.1 Background

9.2

Current Deployment of ITS in the Philippines 9.2.1 Traffic-Responsive Signal System 9.2.2 The Metro Manila ETC Systems

9.3

Road Pricing 9.3.1 Time-Based Fees 9.3.2 Phasing in Peak-Hour Road Pricing 9.3.3 Other Effects of Pear-Hour Road Pricing 9.3.4 MMUTIS Studies on Road Pricing

9.4

Some Issues Related to Sustainable Deployment of ITS In Developing Countries

9.5

Conditions for Acceptable Deployment/Implementation Of ITS in Metro Manila

9.6

Conclusion

References GLOSSARY OF TERMS THE AUTHOR

This work is dedicated to …

My Lord God Almighty – the Way (John 10:35), the light unto my Path (Psalms 119:105)

My wife, Helen – my faithful journey companion (Proverbs 31: 25-28)

Our children, Karen, Paul, and Luke – my arrows in my warrior hand (Psalms 127:3-5)

― And

I will make all My mountains a road, and My highways will be raised up. Behold, these

shall came forth from afar; and o, these will come from the north and from the west…‖ (Isaiah 49:11-12)

PREFACE

The scarcity of books on transportation, especially those particularly relevant and appropriate to Philippine setting, has been a legitimate complaint of students, educators, and practitioners. While it is true that transportation engineering is a young field relative to other civil engineering disciplines, the demand for good education and training on the field escalates due to fast urbanization. As cities and towns grow and develop, the problems related to transport and traffic intensifies in geometric proportions. To avoid costly and, at times, irreversible mistakes, a solid foundation in traffic engineering is a must. We cannot continue to rely on reactionary or trial-and-error approach to our road and traffic woes. Only through a firm grasp and systematic application of basic knowledge and theories could we truly come up with credible and effective solutions. Only through systematic evaluation and research could we discard ineffective designs, improve our skills, and upgrade our systems. The book includes basic concepts that a senior civil engineering student is expected to thoroughly understand. Topics like queuing and shock wave theories are rather advanced, but the basic formulations are presented and conceptualized in simplified manner that even undergraduate students can easily comprehend. It is likewise written to be a handy self-contained reference or easy guide for practicing traffic engineers. A notable recurring theme woven into all discussions is road order and safety. In the quest for efficiency, sophistication, or cost effectiveness, basic safety and orderliness must never be compromised. Accident prevention should always be the first and foremost concern in every design. Preservation of human life remains the most vital aim of a good traffic engineer. We are faced with myriads of transportation and traffic problems: congestion, pollution, energy, inadequate public transportation — the list is endless. Even more affluent countries are not devoid of transportation problems, in varying degrees and forms. But, universally, there is nothing more gratifying than having the field of traffic engineering help meet the needs of our communities toward acquiring not only road efficiency but also a safer and more orderly road environment. The completion of this book would not have been possible without the valuable assistance of the following:

The University of the Philippines Office of the Vice President for Academic Affairs, for the textbook writing grant; The UP College of Engineering (COE) and the UP National Center for Transportation Studies (NCTS), formerly the Transport Training Center, for having been the venue all throughout these years for my teaching and honing the substance of the basic concepts. Colleagues in the UP COE and NCTS, for their encouragement and full support as I wrote the details of each chapter; Civil engineering professors in other universities, for stressing the need for a local book in transportation engineering; Partners in national agencies and the private sector, for providing statistics, photos, and other reference materials; and The UP Press editorial staffs, for the painstaking work of editing and layouting the manuscript.

R. G. Sigua

1: INTRODUCTION

1.1 BACKGROUND

The Philippines, a member of the Association of Southeast Asian Nations, is an archipelagic country consisting of more than 7,100 islands. With a total land area of about 300,000 sq. km, it has 81 provinces, 136 cities, and 1,494 municipalities (NSCB 2007). Metro Manila is the seat of the government and the primary center of business and trade. Other urban centers include the major cities of Cebu and Davao (see figure 1.1). The population of the Philippines is about 80 million, with a growth rate of 2.2 percent per annum. The population density stands at 227 persons/sq. km. Metro Manila comprises sixteen cities and one municipality (NSCB 2007). Its land area is 636 sq. km, and it has a population of 10.4 million. This implies that about 14 percent of the country’s population is concentrated in only 0.3 percent of the country’s land area. Its population density is about 16,000 persons/sq. km, one of the highest in Southeast Asia. The population growth rate is about 3 percent, higher than the national average (ALMEC Corp. 1999).

1.1.1 Road Transport Network

Some 80 percent of domestic passenger traffic and 60 percent of freight traffic currently use the road, and 75 percent of government expenditures on transport infrastructure goes to road systems 9Abueva 2004). The Philippines has a total road length of about 161,000 km, with an average road density of 0.53 km/sq. km or 2.35 km per 1,000 people. Philippine roads are mostly made of concrete pavement. Due to heavy, overloaded trucks, pavements are often damaged, a factor that contributes to traffic accidents. Due to a long rainy season, floods occur throughout the Philippines, Floodwaters often cause damage to road pavements due to inadequate drainage. There are about 11,500 bridges in the national network (measuring about 335,500 lineal meters), of which 1,700 bridges are temporary (DPWH 2004).

1: INTRODUCTION

Figure 1.1 The Philippines (Metro Manila inset)

1: INTRODUCTION

Metro Manila has a total road length of about 4,800 km. The major arterial roads form circumferential and radial patterns, although road expan sion is seen toward the north and south directions, following the development of Metro Manila. Figure 1.2 shows the major road network of Metro Manila with daily traffic. Many of the roads have reached their capacity. Due to traffic congestion, the average travel speed is estimated to be as low as 14 kph, with roughly one-third of the travel time wasted as idle time (Sigua 1997). A typical urban travel in Metro Manila is shown in figure 1.3. According to the 2000 study of the University of the Philippines National Center for Transportation Studies, traffic congestion in Metro Manila has caused more than P101 billion in losses. The condition of the roads in Metro Manila is generally good while it is poorer outside the metropolis.

Figure 1.3 Typical urban travel in Metro Manila

1: INTRODUCTION

1.1.2 Public Transportation

The mode of public transportation in Metro Manila is predominantly road-based, consisting largely of jeepneys and buses for primary and secondary routes, and motorized tricycles and pedicabs for feeder routes. There are about 330 bus routes and 600 jeepney routes. These routes include those serving the adjoining areas of Metro Manila. The jeepneys cover more than 610 km of roads while buses operate mainly on about 350km of roads (ALMEC Corp 1999). Figure 1.4 shows the major bus and jeepney routes. During rush hours, the inadequate provision of public transportation becomes apparent. Many commuters can be seen standing on the carriageway while waiting for buses and jeepneys. Passengers clinging to anything at the back of jeepneys are a common sight.

1.1.3

Traffic Management

Traffic control devices such as traffic signs and markings generally follow the international standard, the Philippines being a signatory to the Vienna Convention in 1968. However, many of the signs installed conform neither to color nor shape as provided for in the standard. The number of traffic signs installed is generally insufficient. In highly urbanized areas, these signs can hardly be recognized, much less read, as they compete with giant billboards in terms of visibility and craftsmanship. Traffic signals are commonly installed at major intersections in many cities and towns in the Philippines although the number is still inadequate. Oftentimes, these signals do not provide display phase exclusive for pedestrians. In Metro Manila, there is a growing concern about the safety of pedestrians due to the closure of intersections and with the U-turn slot scheme replacing the control of traffic signals. Pedestrians have practically no opportunity to cross the road because of the “uninterrupted” flow of traffic. Without traffic signals controlling the traffic flow at intersections, driving has become riskier because of frequent swerving/weaving. There is an urgent need to evaluate the effectiveness of the scheme, which has the sole purpose of improving speed along the arterials without consideration of safety.

1: INTRODUCTION

1.1.4

Pedestrian Facilities

Sidewalks are in relatively good condition; however, many obstructions can be found on them such as illegal vendors, electrical posts, police outpost, etc. With the sidewalk occupied, pedestrians have to walk on the carriageway. There are still very few overhead pedestrian bridges even in Metro Manila and at places where these have been constructed, pedestrians still prefer to risk their lives or limbs by crossing the road at grade level. Moreover, pedestrian overpasses are often inaccessible to the elderly and the handicapped.

1: INTRODUCTION

Figure 1.5 A pedestrian overpass in Metro Manila (Photo taken by the author)

1.1.5

Vehicle Registration

The registration of vehicles in the Philippines is handled by the Land Transportation Office (LTO), a line agency of the Department Transportation and Communication (DOTC). Table 1.1 shows the number of registered motor vehicles in the Philippines in 2002. The number of utility vehicles or jeepneys has a share of 37 percent. The number of motorcycles has increased tremendously in the last three years due to the influx of cheaper models into the country. It reached the 1.5 million mark in 2002. However, this number accounts for both the motorcycles (MCs) for private use and tricycles (TCs) for public transport use. There is therefore a need to separate the categories since they serve completely different purposes.

Table 1.1

Total registration of motor vehicles for 2002 Type

Cars UV SUV Trucks Buses MC/TC TOTAL Source: LTO 2005

Number 749,553 1,554,619 97,695 257,774 33,915 1,470,383 4,163,939

%

18.00 37.34 2.35 6.19 0.81 35.31 100.00

1: INTRODUCTION

About 40 percent of the total numbers of vehicles are registered in Metro Manila. Motor vehicles are classified as follows: 

Private vehicles – refers to motor vehicles owned by private individuals or companies and are not intended to be used for hire.



For hire vehicles – refers to motor vehicles authorized to be used as public vehicles by virtue of a franchise granted by the Land Transportation Franchising and Regulatory Board (LTFRB).



Official/Government Vehicles – refers to motor vehicles owned by the Philippine government.



Diplomatic Vehicles – refers to motor vehicles owned by a foreign government or by their diplomatic officials in the Philippines.

1.1.6 Insurance

Motor vehicle owners are required to obtain insurance covering third-party liabilities. The minimum insurance to be paid to victims of traffic accidents (fatal) was P50, 000 in 2002. The Insurance Surely Association of the Philippines under the Office of the Insurance Commissioner accredited 112 insurance companies all over the Philippines by 2002. It regulates the industry to prevent the proliferation of fly-by-night insurance companies.

1.1.7 Driving License

The issuing procedure of driving license in provided for under Republic Act (RA) 4136. The LTO has the full responsibility for issuance of driving licenses. There are three types of driving licenses: student driver’s permit, nonprofessional driver’s license, and professional driver’s license.

a. Student driver’s permit The applicant must be at least sixteen years old and must be physically and mentally fit to operate a motor vehicle. He or she must be able to read and write in Filipino or English.

1: INTRODUCTION

b. Nonprofessional driver’s license New applicant must be at least seventeen years old and must be a holder of a valid student permit for at least one month. He or she must be physically and mentally fit to operate a motor vehicle, and must not be a drug user or an alcoholic.

c. Professional driver’s license New applicant for professional driver’s license must be at least eighteen years old and is required to submit a valid nonprofessional driver’s license or a valid student driver’s permit that is used for at least five months. He or she must not be a drug user or an alcoholic. The requirement of having a medical examination and drug test was introduced only very recently.

Driving license requirements The holder of a student driver’s permit is only allowed to operate a motor vehicle if accompanied by a licensed driver who is liable for any damage caused by the student driver’s operation of the motor vehicle. A student driver’s permit is good for only one year while the nonprofessional and professional driver’s licenses are valid for three years, expiring on license holder’s birth month. License holders are required to renew their license before the expiry date.

Written and practical examinations Applicants for nonprofessional and professional driver’s licenses are required to pass both written and practical examinations. The written examination is given to gauge the applicant’s knowledge of traffic rules and regulations based on the Traffic Code, safe driving practices, and the mechanics of motor vehicles. The written test for nonprofessional driver’s license applicants has forty questions, and candidates must be able to answer at least thirty questions correctly. In the case of the professional driver’s license applicants, sixty questions are given, and applicants must be able to get at least forty-five correct answers to pass the test. The practical examination is given to test a candidate’s ability to park a vehicle properly, to start on slope, etc.

1: INTRODUCTION

The total number of professional licenses, nonprofessional licenses, and student permits issued in 2002 was about 2.9 million. The breakdown is shown in figure 1.6.

Figure 1.6 Breakdown of driver licenses and permits issued in 2002

1.1.8 Driver Apprehensions

There seems to be an increasing trend in the number of drivers apprehended (table 1.2). This could be attributed to the concerted efforts of the different agencies (the Land Transportation Office, the Metro Manila Development Authority [MMDA], and the Philippine National Police – Traffic Management Group [PNP-TMG]) in apprehending violators over the past years.

Table 1.2

Number of apprehended drivers Year

1999 2000 2001 2002

Total

480,122 475,626 570,748 612,477

Source:LT0 2005

As to the type of apprehensions, most of these are fines for violating traffic rules and regulations (table 1.3)

1: INTRODUCTION

Table 1.3

Breakdown of types of driver apprehension (1999-2002) Type Fined Suspended license Revoked license Impounded vehicle Others

Number 594,126 345 4,447 5,771 34,933

% 92.89 0.05 0.70 0.90 5.46

Source:LTO 2005

1.1.9 Driving Schools

Driving schools and driving instructors must have accreditation from the LTO. In 1980, the then Ministry of Transportation and Communications (MOTC) issued an order covering the rules and regulations governing the supervision and control over driving schools. Standard requirements were set fourth for driving site, school building, classrooms, library facilities, motor vehicles, instructors, and course of instruction. In 2002, about 170 LTO-accredited driving schools were in operation all over the country.

1.1.10 Traffic enforcement

Traffic laws are enforced by the Traffic Management Group (TMG), the traffic division of each district police, and the LTO. In 1978, Presidential Decree (PD) 1605 was issued to centralize enforcement matters in Metro Manila to the Metro Manila Commission (MMC), now the Metro Manila Development Authority. The TMG, being a national support unit of the PNP, has traffic management offices scattered in the different regions and provinces nationwide. In selected areas or provinces, especially in highly urbanized cities/municipalities, the TMG has traffic management teams (TMTs) that are also capable of performing the functions of the TMG operational support units that are likewise based in Metro Manila. In coordination and cooperation with the MMDA for Metro Manila and the local police units in the different regions, the TMG has at its disposal the traffic enforcement units. Each Regional Traffic Management Office (RTMO) can dispatch

1: INTRODUCTION

personnel to strategic choke points and major thoroughfares to conduct traffic direction and control to ensure the smooth flow of traffic. In Metro Manila, the TMG and the MMDA assist each other in traffic management, especially when on-going infrastructure projects cause heavy congestion. Alongside this function, the personnel of TMG render the following tasks: traffic accident investigation, and the traffic safety education through seminars and conferences, etc.

1.1.11 Legislative Framework

This section discusses some of the legislations pertinent to road safety (Santiago 1980). Republic Act 4136, otherwise known as the Land Transportation and Traffic Code, provides for the system of registration of motor vehicles, checks on accessories of vehicles, and defines road traffic rules and regulations. Commonwealth Act 146, otherwise known as Pubic Service Act, rests on the regulatory body (LTFRB) the power to compel any public service provider to furnish safe, adequate, and proper service as regards the manner of furnishing the same as well as the maintenance of necessary materials and equipment. Executive Order (EO) 125 reorganized the then Ministry of Transportation and Communications into a Department and defined its powers and functions, including the establishment of the Land Transportation Office as the sectoral agency responsible for implementing and carrying out policies, rules, and regulations governing the land transportation system of the country. Executive Order (EO) 202 created the Land Transportation Franchising and Regulatory Board with the main function of regulating the land transport industry pursuant to the Public Service Act. Republic Act 6975 established the Department of the Interior and Local Government (DILG), including the creation of the PNP under which the Traffic Management Group has been reorganized as the traffic enforcement arm of the PNP covering national roads.

1: INTRODUCTION

1.2 TRANSPORTATION AND TRAFFIC ENGINNERING PRACTICE

1.2.2 Definitions

Transportation engineering is a filed or branch of civil engineering that deals with the application of technology and scientific principles to the planning, functional design, operation, and management of facilities for any mode of transportation in order to provide for the safe, rapid, comfortable, convenient, economical, and environmentally compatible movement of people and goods. On the other hand, traffic engineering is that phases of transportation engineering that deals with the planning, geometric design, and traffic operations of roads, streets and highways, their networks, terminals, abutting lands, and relationships with other modes of transportation (Evans 1950). In the United States, it was in 1921 when the title “traffic engineer” was first recognized, although a number of traffic engineering-related activities were already going on. Table 1.4 shows some of these activities:

Table 1.4

Milestones in the developing profession of traffic engineering Year 1904 1907 1908 1911 1915 1916

Activity Traffic survey methods were being employed. Pedestrian islands were used in San Francisco. The first driver’s license law was adopted. White-painted pavement center lines were first applied. Origin-destination studies and accident spot maps were first used. Speed and delay study was first made by observing traffic from a high building; pedestrian regulation and “no left turns” were prescribed; curb parking was prohibited to facilitate traffic movement.

Source: Evans 1950

The use of traffic signals for controlling traffic came much earlier. The first recorded use of traffic signals was in 1868 in Great Britain. The signals were illuminated by town gas. However, the use of gas was discontinued after an explosion incident. The development of traffic signal technology is shown in table 1.5.

1: INTRODUCTION

Table 1.5

Development of traffic signal control Year 1868 1910 1922 1926 1927

1928

Activity First traffic signal in Great Britain (illuminated by gas) Manually operated semaphore signals Idea of timing signals for progressive movement First automatic traffic signals in Great Britain Earliest known application of time-space diagram coordination First traffic-actuated signals

for

Source: Evans 1950.

In 1930, the Institute of Traffic Engineers (ITE) was founded, and traffic engineering as a profession was finally officially established and defined. The society played a key role in promoting the profession through advanced training, research studies, standardization, laws, and application of traffic engineering techniques (Evans 1950).

1.2.3

Traffic Engineering in the Philippines

The traffic engineering practice in the Philippines is still new. Most intersections were previously controlled by traffic police officers or by manually operated traffic signals. Outside Metro Manila, manually operated semaphore signals displaying STOP or GO message were installed on top of police outposts located at the center of the intersection. In 1977, the Traffic Engineering and Management (TEAM) Project first implemented an area traffic control system in Metro Manila. It was almost at the same period when the Traffic Control Center, later renamed as the Traffic Engineering Center (TEC), was established. The center was responsible for the implementation of various traffic engineering and management measures such as traffic signalization, geometric improvement of intersections, etc. In 1976, the Transport Training Center (TTC) was established in the University of the Philippines with assistance from Japan through the Japan International Cooperation Agency (JICA). TTC started its training program in 1978 in the fields of traffic engineering, transportation planning, and traffic management for traffic law enforcers. TTC was renamed as the National Center for Transportation Studies and became a regular unit of UP Diliman in 1993, with research and support to graduate programs in the fields of transportation engineering and transportation planning as additional functions.

1: INTRODUCTION

REFERENCES



Abueva, Jose V., ed, 2004. The Macapagal-Arroyo presidency and administration: Record and legacy (2001-2004). Vol. 1. Quezon City: UP Press.



ALMEC Corporation. 1999. Metro Manila Urban Transportation Integration Study (MMUTIS) final report.



Department of Public Works and Highways (DPWH). 2004. Infrastructure atlas 2004.



Evans, Henry K., ed. 1950. Traffic engineering handbook, Second ed, New Haven, Connecticut: Institute of Traffic Engineers.

 

Land Transportation Office, 2005. Statistics, Unpublished. National Center for Transportation Studies (NCTS). 2000. A study on cost of traffic congestion in Metro Manila, Quezon City: NCTS.



National

Statistical

Coordination

Board

(NSCB).

2007.

NSCB

website.

http://www.nscb.gov.ph. 

Santiago,Mariano R., ed. 1980. A compilation of edicts related to the land transportation system of the Philippines. Quezon City: Bureau of Land Transportation.



Sigua, Ricardo G. 1997. Development of driving cycle for Metro Manila. Journal of the eastern Asia Society for Transportation Studies 2, no 4. Seoul: Eastern Asia Society for Transportation Studies (EASTS).

2: TRAFFIC MANAGEMENT

2.1 INTRODUCTION

Traffic management is a term used to embody the activities undertaken by a highway transportation agency to improve roadway system safety, efficiency and effectiveness for both providers and consumers of transportation services. There are two distinct types of traffic management. The first one is through the use of traditional traffic engineering tools or simple devices to regulate and control traffic. The second relies more on simple devices to regulate and control traffic. The second relies more on advanced technology through the use of Intelligent Transportation Systems (ITS). Advancement of ITS has been the primary goal of many developed countries. The more conventional applications are common in developing countries. However, it is not uncommon in both developed and developing countries to have a combination of conventional methods and ITS application. AN introduction to ITS is provided in chapter 9.

2.2 TRAFFIC REGULATIONS

Many individuals feel that traffic controls are an encroachment on their individual driving rights. It must be stressed, however, that driving is not a right but a privilege. It is therefore necessary to show that restrictions are for the general welfare, and it must be demonstrated that regulations do not curtail the rights or actions of the majority. Traffic regulation must cover all aspects of the control of both vehicle (registration, ownership, mechanical fitness, accessories, size, and weight) and driver (age, ability to operate specific types of vehicles, financial responsibility). Traffic regulations must be reasonable and effective. This can only be achieved through careful study. Facts must be sought through the conduct of traffic studies, accident analysis, keeping driver records, and other data.


All traffic regulations are dependent upon the laws of the states and local governments, especially the ordinances of cities. Legislative bodies and traffic authorities must keep in mind that unreasonable restrictions or regulations are not likely to last very long.

2.2.1 Effective Traffic Regulation There are fundamental requirements for traffic regulation to be effective. These are as follows: a. Regulation should be rational. Irrational regulations cannot be enforces except by tremendous effort and expense. Social, economic, and human problems must be considered. If the habits of a community are greatly at variance with the regulations, success cannot be attained for an y substantial period of time. b. Regulations should be developed progressively. Regulations must be planned over a long period of time, and the effects must be carefully observed so that alterations can be made as experience dictates. Experience shows that abrupt changes in regulation often lead to increase in the occurrence of traffic accidents. c. Regulations alone often are not enough. Regulations constitute but one approach to the overall traffic problem. When public acceptance is poor and enforcement is lax, regulations may be totally ineffective. They must be used in conjunction with control devices, overall highway planning and design, and administrative policies.

2.2.2 Three Elements of the Road System The road system consists of the following, a. The road b. The vehicle c. The driver

Figure 2.1 suggests a balance among the three elements, i.e., a breakdown or deficiency in one can lead to the failure of the entire system.


Figure 2.1 Interaction of the three elements of the road system

The road and vehicle may be subject to constant change and improvement. However, in a given period of time, they may be considered inflexible. The major portion of existing regulations is therefore aimed at the driver. Worldwide, licensing has become the most effective way of controlling the number of drivers on the road. It should be used, therefore, to influence drivers to become familiar with the rules of the road. This is especially true for the Filipino drivers, considering the most accidents have been attributed to them. For vehicles, a number of controls exist, the most effective of which is vehicle registration. Others are checks on equipment and accessories (lights, bells, mirrors, helmets, etc.), and vehicle’s dimension and weight. Currently, the Motor Vehicle Inspection System (MVIS) is being revitalized and expanded to cover the whole country.

2.3 TRAFFIC CONTROL DEVICES

Traffic control devices are means by which the road user is advised as to detailed requirements or conditions affecting road use at specific places and times to that proper action may be taken and accident or delay avoided. There are three distinct functional groups of traffic control devices:


a. Regulatory devices These have the authority of law and impose precise requirements upon the actions of the road user. b. Warning devices These are used to inform road users of potentially hazardous roadway conditions or unusual traffic movements that are not readily apparent to passing traffic. c. Guiding devices These are employed simply to inform the road user of route, destination, and other pertinent traffic.

2.3.1 Four Elementary Requirements of Every Traffic Control Device To be effective, every traffic control device must be able to meet the following requirements (FHWA 1988): a. It should compel attention. b. It should convey a simple clear meaning at a glance. c. It should allow adequate time for easy response. d. It should command the respect of the road users for whom it is intended.

Every traffic control must meet all these requirements in logical sequence. The effectiveness of a sign or marking normally depends on its size, color contrast, shape (simple, regular shapes), relative position, and maintenance to compel attention. To convey a clear meaning, the shape, color, and message must be well understood. The message should be kept as short as practicable at a glance. After capturing the clear meaning of the device, it should provide adequate time for response. Simpler message like STOP or YIELD requires only a second, while multiple choice (as in destination or guide sign) may require three to four seconds. Finally, all these requirements – the design features of size and brightness, position allowing time for response, properly maintained control device – should command the respect of road users. Thus, shabby, ill-kept signs must be discarded and replaced.


2.4 TRAFFIC SIGNS AND MARKINGS

Traffic signs are employed more frequently than any other devices to regulate, warn, or guide road users. Traffic markings normally consist of lines, patterns, words, symbols, reflectors, etc. They may be considered as specialized types of traffic signs in which the message is in contrast with the color and brightness of the pavement or other background. Philippine traffic signs conform to the 1968 Vienna Conventions of the United Nations on Road Traffic and Road Signs, which the country officially adopted on June 6, 1973. Traffic signs are necessary to give information as to routes, directions, destinations, etc. Their function becomes more relevant when used to warn road users of hazards and regulate any prohibitive action at specific places and/or at specified times. To ensure uniformity, traffic signs shall be installed only by a duly authorized public body or official for the purpose of guiding, regulating, and warning traffic. In case of temporary construction work, however, special permission is given to contractors or utility companies to install signs to protect the public provided that such signs conform to the set standards. Traffic signs are normally of fixed/permanent type although some variable signs have been employed and have become useful in locations where traffic and environment conditions often change. Traffic signs are classified depending on their intended uses:

a.

Informative: the signs are intended to guide users while they are traveling.

b.

Regulatory: the signs are intended to inform users of special obligations, restrictions, or prohibitions with which they must comply.

c.

Warning: these signs are intended to warn users of a danger on the road and to inform them of its nature,

2.4.1 Elements of design Uniformity in design includes shape, color, dimension, symbols, wording, lettering, and illumination or reflectorization.

Shape Shapes of signs are standardized as follows:


a) Equilateral triangular shape with one side horizontal shall be used for danger warning signs. b) Round shape shall be used for regulating traffic. c) Rectangular shape shall be used for informative signs. d) Octagonal shape shall be used for STOP signs only. e) Inverted equilateral triangle shall be used for YIELD signs only.

Color 

Danger warning signs shall have a yellow or white background with black symbols and red border.



Prohibitory signs and restrictive signs shall have a white background with black symbols and red border.



Mandatory signs with the exception of STOP and YIELD signs shall have a blue background and white symbols.



STOP signs shall have a red background and white symbols.



YIELD signs shall have a yellow background and red border.



Informative signs shall have a white or light-colored symbol on a dark-colored (blue or black) background or a blue or dark-colored symbol on a white or light-colored background.

Size The minimum dimensions of signs depend upon the intended applications. Larger sizes are necessary at wider roadways and on high speed highways. According to section 2.5 of DPWH Highway Safety Design Standards Part 2: Road Signs and Pavement Markings Manual , regulatory signs are of four sizes based on the speed of the facility as follows: a. A for urban low-speed roads b. B for rural roads with speed limits between 60 kph and 70 kph c. C for high-speed rural highways d. D for expressways

In the case of a STOP or YIELD sign, for example, table 2.1 below should be followed:


Table 2.1 Recommended dimensions for STOP and YIELD signs SIZE A B C

DIMENSION (mm) 600 x 600 750 x 750 900 x 900

Source: DPWH 2004.

The reader is advised to refer to the DPWH manual for the dimensions of various traffic signs and for other details – letter, symbol, border, bar sizes, etc.

Illumination and reflectorization Signs are intended to convey messages during both daytime and night time. During hours of darkness, this can be achieved through illumination or by using reflective materials for signs.

Placement and height of signs In general, signs shall be mounted approximately at right angles to the direction, and facing the traffic they intended to serve. Mounting signs at exactly right angle must be avoided especially on roads following the east and west directions as the sun’s brightness reflecting on the signs will be too glaring for the drivers. However, there may be no standard location for traffic signs. Each location must be carefully studied so as to achieve the most advantageous position. Signs are generally placed on the right side of the roadway. On wider roads, overhead signs are often necessary. On roads with medians, signs may be placed on both sides. Signs may also be placed on channelized islands. a. Lateral placement On uncurbed roads in the rural areas, the sign should be at least 60 cm clear of the outer edge of the road shoulder, the line of guideposts, or face of guardrails. The clearance should not be less than 2 m nor more than 5 m from the edge of the travelled way, except for large guide signs on expressways where ample clearance may be required (see figure 2.2). In urban areas, signs should be located away from the face of the curb not less than 30 cm but not more than 1 m. If curb is mountable or semi mountable, the minimum clearance should be 50 cm. On uncurbed roads, the distance given for rural areas shall be used.


b. Height In rural areas, the height of the sign should normally be between 1 m and 1.5 m above the nearest edge of the travelled way. For intersection direction signs, the height should be increased to 2 m. Final height is dictated by visibility factor as the sign should be mounted clear of vegetation and it must be clearly visible under headlight illumination at night (see figure 2.2). On curbed roads such as in urban areas, the signs should be mounted at a minimum of 2 m above the top of the curb to prevent obstructions to pedestrians.

Figure 2.2 Height and lateral placement of signs

c. Location of advance warning signs In urban areas, warning signs should be placed no less than 30 m but more than 100 m in advance of the hazardous area, while in rural areas they should be placed no less than 75 m but no more than 225 m ahead of the hazardous area. The final location shall be determined based on the nature of the hazard, reaction time, and operating speed in the area.


2.5 INTERNATIONAL STANDARD TRAFFIC SIGNS

2.5.1 Warning Signs The Vienna Convention allows two forms for the warning sign – one is triangular on shape with a red border and the other is a diamond in shape (table 2.2). Upon signing in the convention, the signatory has to state which shape is to be adopted. In the Philippines, the first form is the one being used although the second may still be found in rural areas. The coloring may also differ in each form. However, the choice of color is left to discretion of the signing body. Examples of warning signs are shown in table 2.3. Table 2.2 Shapes and colors of warning signs

a.

b. Some countries use this sign; some only for temporary messages.

c.

d. Coloring is not approved by the convention but is generally used for temporary messages.


Table 2.3 Examples of warning signs


2.5.2 Priority Signs Priority signs have various forms. The two most commonly used priority signs are the STOP and YIELD signs (table 2.4). Table 2.4 Example of priority signs

2.5.3 Prohibition Signs Prohibition signs are round with a red border and either a white or a yellow background. Access restrictions signs can have a red bar from low right to top left. Parking prohibitions have a blue background. The signs that signal the end of a prohibition are white or yellow with a small black border and a black bar form left below to right top. The bar can be replaced by a series of small bars. In addition, the symbol for which the end of prohibition is intended is given in gray. Examples of prohibition signs are shown in table 2.5. Table 2.5 Examples of prohibition signs


Table 2.5 (continued)


2.5.4 Obligatory Signs The obligatory signs are round and in blue colors. Examples are shown in table 2.6. Table 2.6 Examples of obligatory signs



2.5.5 Other Prescription Signs These signs are, in general, rectangular with either a blue base with a white background, or with a light base with a dark foreground. These signs give prohibitions, obligations, or danger messages for particular lanes on a multilane road. Each lane is represented by an arrow, to which the appropriate sign is affixed. Table 3.7 shows some examples. The background color blue is used for major roads, white for minor roads, and within built-up areas, and yellow for road works. Table 2.7 Examples of prescription signs




2.5.6 Information Signs These signs are rectangular with a white or yellow plate with a symbol that stands for the service involved. The signs can be either blue or green. Examples are shown in table 2.8. Table 2.8 Examples of information signs


2.5.7 Direction Signs A profusion of colors and forms is available. In general, the forms shown must be adopted, and in some cases even the color shown must be used and not be changed. Table 2.9 Examples of directional signs

2.5.8 Additional Information These signs are small and rectangular, they supplement the information on the main sign (table 2.10). Table 2.10 Examples of supplemental signs


2.6 PAVEMENT MARKINGS

2.6.1 Functions and Limitations of Pavement Markings

A system of clear and effective pavement markings is essential for the guidance and control of vehicles and pedestrians. They take the form of lines, symbols, messages, or numerals, and may be set into the surface of, applied upon, or attached to the pavement. In some cases, pavement markings are used as a supplement to other traffic control devices such as traffic signals and road signs. In other instances, they may simply guide traffic regulations. Pavement markings have some definite limitations: a. They are subject to traffic wear and require proper maintenance. b. They may not be clearly visible if the road is wet or dusty (e.g., near shoulder edge or median). c. They may be obscured by traffic. d. Their effect on skid resistance requires careful choice of materials. e. They cannot be applied on unsealed roads. Despite these limitations, they have the advantage under favorable conditions of conveying warning message or information to drivers without diverting their attention from the road.

2.6.2 Legal Authority

Markings shall only be applied and/or removed by the Department of Public Works and Highways (DPWH) or an authority to which these powers are delegated. All line-markings plans must be approved by the DPWH before installation.

2.6.3 Standardization

As in the case with all other traffic control devices, it is imperative that markings be uniform so that they may be recognized and understood instantly by all drivers. Manuals are available from the DPWH, and on request, it will furnish traffic authorities, road markers, material


suppliers/manufacturers, and similarly interested agencies, detailed drawings of the standard designs and locations.

2.6.4 Types of Markings

Markings are classified into the following groups: 

Pavement and curb markings a. Longitudinal lines are those laid in the direction of travel. These include Center Line, Lane Line, Double Yellow Line, “No-Passing” Zone Markings, Pavement Edge Line, Continuity Lines, and Transition Line. b. Transverse lines are those laid across the direction of travel. These include Stop Line, Yield (Give Way) Lines, and Pedestrian Crossing Markings. c. Other lines, which include Turn Lines, Parking Bays, Painted Median Islands, and Bus & PUJ Lane Lines. d. Other markings, which include Approach Markings to Islands and Obstructions, Chevron Markings, Diagonal Markings, Markings on Exit and Entrance Ramps, Curb Markings for Parking Restrictions, Approach to Railroad Crossings, Messages, and Symbols and Pavement Arrows.



Object markings a. Object within the roadway b. Object adjacent to the roadway



Reflector markings a. Retro-reflector raised pavement markers b. Hazard markers c. Delineators

2.6.5 Materials

Road markings should be of non-skid materials and should not protrude more than 6 mm above the level of the carriageway. Raised pavement markings should not protrude more than 15


mm above the level of the carriageway. The following are the commonly used materials for road markings: 

Paint Paint with or without glass beads embedded or premixed can be applied either by hand or with line marking machines, For proper reflectorization at night, the amount of glass beads used should be less than 0.45 kg and no more than 0.50 kg per liter of mixed paint.



Thermoplastic materials Use of thermoplastic materials with or without reflective properties is recommended at locations subject to extreme traffic property is recommended at locations subject to extreme traffic wear. The average service life of thermoplastic materials has been experienced to be equivalent to eight times that of beaded traffic paints.



Pre-cut sheeting Pre-cut materials both with or without reflective properties are used. It is usually in adhesive tape form, with aggregate, pigment, and plastic rubber combined on one side and adhesive on the other side.



Raised pavement markers These are studs of plastic, ceramic, aluminum, cast iron, etc. that are embodied into the carriageway or attached to the road surface with adhesive. They may be reflective or nonreflective.

2.6.6 Color

The color of pavement markings shall be white, except for the alternative uses of yellow in the following cases: a. Double yellow “no- passing” lines b. Unbroken portion of “no- parking” lines c. Curb markings for prohibition of parking d. On island in line of traffic e. Bus and PUJ lanes Black may be used in combination with white or yellow in hazard markers to warn drivers at locations where the protruding objects – such as bridge piers, traffic islands, or other protruding


objects – on or near the roadway. However, the use of black does not establish it as a standard color for pavement marking.

2.6.7 Types of Lines

Depending on the direction that lines are marked on the pavement, lines may be longitudinal, transverse, or oblique. And depending on the use and meaning of such lines, they are either broken or solid lines. A broken line shall consist of line segments of equal lengths separated by uniform gaps. The speed of vehicles on the section of road or in the area in question should be taken into account in determining the lengths of the strokes and of the gaps between them. A solid unbroken line is used where crossing of the line is either discouraged or prohibited. It is generally used to replace or supplement a broken line where required, e.g., barrier lines, center lines, etc. Solid lines may be either yellow or white, depending whether crossing the line is legally prohibited or not.

2.6.8 Width of Lines

The width of solid or broken lines varies from 100 mm to 300 mm, depending on the usage of the specified line. Transverse lines are usually wider because of the angle at which the driver sees markings on the carriageway.

2.6.9 Messages

Messages when used should be limited to as few words as possible, never more than three. they shall only be used so supplement other traffic control devices. The distance between words is variable, depending on the message and location at which it is based. (Usually twice the length of the word if achievable.) The first word of the message is to be nearest the motorist on rural roads. Un urban lowspeed areas, the order is optional.


Messages are white in color. Letters or numerals used on roads in urban areas shall measure at least 2.5 m; oh high-speed highways, they may need to be at least 5 m. Messages generally in use are STOP, KEEP CLEAR, SCHOOL PED XING, RAILROD XING, SIGNAL AHEAD, NO RIGHT (LEFT) TURN, BUS LANE, and PUJ LANE.

2.6.7 Symbols

a. Give way (yield) symbol The symbol used to supplement the give way sign consists of isosceles triangle having two equal sides of 3.1 m and a base of 1 m. Outline width is 450 mm at the base and 150 mm for the sides. The distance of the symbol from the holding line is between 5 m and 25 m, depending on the location and vehicle speeds on that road.

b. Pavement arrows Pavement arrows are used for lane use control. White in color, they are generally 5m in length on urban roads and 7.5m on high-speed roads. For half-turn movements, the stems of the straight arrows can be bent to suit the particular direction of movements. The first set of arrows should be placed at a distance of 15m from the stop bar, and the supplement sets should be placed at 45m apart.

c. Numerals The only numerals that should be used are those associated with speed limits at location to supplement limit signs, which are continuously disregarded by drivers.

2.7 OBJECT MARKINGS AND MARKERS

2.7.1 Object Markings

Physical obstructions in or near a roadway that constitute serious traffic hazard, including installations designed for the control of traffic, shall be adequately marked. Typical obstructions of


this character are bridge supports, monuments, traffic islands, beacons, signal and sign support, loading islands, railroads and draw-bridge gates, posts of narrow bridges, underpass piers and abutments, culvert headwalls, poles, trees, rocks, and structures giving restricted and overhead clearance. For additional emphasis it is also advisable to mark obstructions rather than islands with reflectorized white paint with not less than five alternating black and reflectorized white stripes. The stripes shall slope downward at an angle of 45 degrees toward the side of obstruction, and shall be uniform and not less than 100 mm in width. A large surface, such as a bridge pier, may require stripes of 300 mm (see figure 2.3).

Figure 2.3 Object markings (Courtesy of R. Rellosa of 3M Phil.)

In addition to the marking on the face of an obstruction in the roadway, warning of approach to the hazard shall be given by line markings on the pavements. Reflectorized yellow should be used in curbs of all islands located in the line of traffic flows especially on curbs directly ahead of traffic at T and offset intersections.

2.7.2 Raised Pavement Markers

Raised pavement markers are small rectangular or dome-shaped devices that are fixed to the pavement surface to simulate or supplement painted pavement markings (figure 2.4). The markers can be reflective or nonreflective.


Figure 2.4 Raised pavement markers (The one on the right has a built-in lightning.) (Left photo courtesy of R. Rellosa of 3M Phil; right photo courtest of Solarmakers Inc.)

Raised pavement markers are generally not obscured at night and under wet conditions. The reflective types are more brilliant than reflectorized paint markings. Because of high cost of installation and maintenance, use of raised pavement markings may be considered only in accident-prone areas, e.g., on hilly areas where there is frequent fog and rain. Figure 2.5 shows the visual effect of raised pavement markers.

Figure 2.5 Visual effect of raised pavement markers in between reflectorized pavement markings (Photo courtesy of R. Rellosa of 3M Phil.)


Hazard markers Hazard markers are rectangular and generally consist of a series of alternating black and white bands (figure 2.6). The white portion is always reflectorized, but the reflectorized material may cover only the central portion of each white band in order to achieve a balance between the areas of black and white under headlight illumination. The bands may consist of either diagonal strips where only a target is required or of chevrons where directional as well as target properties are desirable.

Delineators Delineators are small reflective panels or buttons mounted on guide posts or guard fences as an effective aid for night driving (figure 2.7). Delineators are made of reflective material capable of reflecting light clearly visible under normal atmospheric condition from a distance of 300-500 m when illuminated by the upper beam of a standard automobile head lamp. Placement of delineators at the roadside of a circular curve is shown in figure 2.8.

Figure 2.6 Chevron markers (Photo courtesy of R. Rellosa of 3M Phil.)


Figure 2.7 Delineators made of reflective materials

Figure 2.8 Placement of permanent delineators along a roadway curve.


PROBLEMS

1. Drive along Epifanio de los Santos Avenue (EDSA) or along any major roads in your locality. Note if traffic signs are visible or if they are obscured because of too many advertisement or billboard signs. Must there be regulations on putting up advertisement signs? 2. Nowadays, many local government units have been able to get support from private companies in fabricating and installing traffic signs at locations under their jurisdiction, provided that the company’s logo or identification is indicated in a certain area of the sign (one-eighth to one-fifth of the total surface area). Would you agree to this? Why or why not? 3. In the town or city where you are residing, identify the different traffic signs and see if they conform to the Vienna Convention as to color and shape. Would you agree if these signs do not conform to the international standards because they were fabricated at lower cost in your locality? 4. Most international signs consist mainly of symbols with minimum or almost no words in them. Would you suggest putting words in Tagalog or in any dialects in order to convey their meaning? Why or why not?

REFERENCES



Department of Public Works and Highways (DPWH). 2004. Highway safety design standards. Road Safety Design Manual. Manila: DPWH



Federal Highway Administration (FHWA). US Dept. of Transportation. 1998. Manual on uniform traffic control devices for streets and highways (MUTCD).



Planning and Project Development Office, Ministry of Public Highways. 1980. Manual on pavement markings.



Santiago, Mariano R. ed. 1980. A compilation of educts related to the land transportation system of the Philippines. Quezon City: Bureau of Land Transportation.

3: TRAFFIC FLOW FUNDAMENTALS

3.1 INTRODUCTION

Describing traffic is considered very difficult due to several factors that cause its irregularity or unpredictability. These factors could be attributed to several events which could happen on the road: accidents, stalled vehicles, lane changing or swerving, parking maneuvers, indiscriminate loading and unloading of public utility vehicles, etc. Without these events, traffic flow could be expected to be fairly regular and predictable within a day or even within a week. However, the more frequently these events occur along the road, the harder it is to predict the traffic condition. It is during the occurrence of a traffic event when more advanced knowledge of traffic flow theory, like queuing analysis or shock wave, becomes necessary. These topics will be introduced at the end of the chapter. First, let us consider how we can best describe traffic condition when congestion builds up simply due to continuous increase of traffic density along a road. To illustrate, imagine the development of traffic along the expressway. In the early morning, drivers can freely choose their own speeds because there are only very few vehicles on the road. As traffic density increases, the drivers are constrained to adjust their speeds. Traffic condition becomes very unstable when the capacity of the highway has already been reached, after which, a stop-and-go condition will be experienced if the situation worsens, traffic is brought to a standstill - a complete breakdown of the expressway because of lack of capacity. This condition may last for several minutes or even hours. However, we can expect a reverse process to occur when traffic flow returns to stable condition.

3.2 TYPES OF FLOW

Traffic flow is usually classified as either uninterrupted or interrupted. Flow occurring at long sections of road where vehicles are not required to stop by any cause external to the traffic stream is called uninterrupted flow. On the other hand, flow occurring at intersections or


driveways where vehicles are required to stop by any cause outside the traffic stream - such as traffic signs (STOP or YIELD), traffic signal lights, etc. - is called interrupted flow. For each type of flow, we will discuss the most commonly used traffic variables that best describe them. 3.2.1 Major Traffic Variables Uninterrupted flow can be described using an y of the following traffic variables: A. Flow rate or volume B. Speed C. Density or concentration

Flow rate or volume Flow rate is defined as the number of vehicles passing a point during a specified period of time. It is often referred to as volume when measured over an hour. Figure 3.1 illustrates the trajectories of vehicles traveling in given section L of a one-way road. Consider a point on the road (represented by a line 1-1 drawn transversely). If N vehicles (represented by trajectories crossing line 1-1) passed this point in time T, flow rate q may be expressed as:



 

(3.1)

Again, if the observation period T is set to one hour, q is called volume and will have a unit of vehicles per hour. In general, flow rate (or volume, as used loosely) will have units like vehicles per minute or vehicles per day.

Figure 3.1 Time-distance diagram


Example 3.1 Let us suppose a 15-minute count of vehicles bound for Manila was conducted at a particular location on Quezon Avenue. A summary is shown in the table below: TYPE Car/van Jeepney Bus Truck Estimate the flow rate in vehicles per hour.

15 - MINUTE COUNT 420 300 16 28

Solution: The total number of vehicles counted in 15 minutes is 420 + 300 + 16 + 28 = 764. This is expanded to one hour by multiplying by 4. Therefore, the flow rate is q = 764 x 4 = 3,056 vehicles per hour (Note that the count within the 15-minute interval is assumed to be the same for the other three 15-minute intervals.) Speed Speed is defined as rate of motion in distance per unit time. When describing traffic stream, two types of speed are used: time men speed and space mean speed. a. Time mean speed Also called spot speed, time mean speed is simply the arithmetic mean of the speeds of vehicles passing a point within a given interval of time. Strictly speaking, distance or length of road must be known in order to measure speed. However, with the use of speed radar, spot speed can be measured at a certain point on the road. Also, spot speed can be reasonably measured if a point is approximately by a short distance, say 1550 m of road. This distance is normally called trap length in spot speed studies. With the use of stop watch, the time it takes for the vehicle to traverse this trap length is measured. Individual speed of vehicles is then computed by dividing this trap length by this measured time. Figure 3.2 shows how spot speed is approximated by the use of trap length, Δx.


Figure 3.2 Measuring spot speed using trap-length method Let

ui - speed of vehicle i, kilometer per hour ti - time it takes for vehicle i to transverse the trap length, in seconds Δx - trap length, in meters

then  

 

 

Knowing the individual speeds of n vehicles observed within time T, the time men speed or spot speed of the traffic stream is given by

 

∑   

(3.2)

Example 3.2 The speed of 25 cars was observed. 10 cars were noted to travel at 35 kph, 8 cars at 40 kph, 2 cars at 50 kph, and 5 cars at 45 kph. Assuming that each car was traveling at constant speed, determine the time mean speed

Solution: Applying equation 3.2

 

       



 

  


It is common practice among traffic engineers to report "spot speed" for given location. Spot speed is often used as basis for estab lishing speed limits. b.

Space mean speed Space mean speed is used to describe the rate of movement of a traffic stream within a given section of road. It is the speed based on the average travel time of vehicles in the stream within the section. It is also called the harmonic mean speed. Consider the time-distance diagram shown in figure 3.3. Only the speeds of vehicles intersected by the line drawn at instant time t are measured. (The speed of a vehicle can actually be estimated by dividing the length of the road section L by its travel time.)

Figure 3.3 Time-distance diagram for space men speed

If n vehicles are observed at an instant of time t, the space mean speed is computed as follows:

 

  

∑ 

(3.3)

Example 3.3 Using the same example determine the space mea speed. Solution: Applying equation 3.3:


 

           



 

  

Density Density is defined as the number of vehicles in a given length of road at an instant point in time. Using the same figure 3.3, the number of vehicles counted at time t divided by the length of the section L gives a measure of density in that section. Again, if n vehicles are found within the section L, density k is computed as:



 

(3.4)

Among these three variables, density proves to be the most difficult or expensive to observe. Aerial photography is the most commonly used method to get its exact values. On the other hand, there are various ways of conducting volume and speed studies. (These are discussed in chapter 4.). It will be seen later that these variables are actually related to each other and that density can be derived if volume and speed are known.

3.2.2 Other Traffic Variables There are other variables used to describe traffic flow. These variables, however, are simply variants of the three variables described previously.

Time headway Time headway is defined as the time interval between passage of consecutive vehicles at a specified point on the road with a unit of time per vehicles. Referring again to figure 3.1 where N vehicles were counted to pass line 1-1 within the observation time T, let hi be the time headway of 2 consecutive vehicles. The average headway representing all observed vehicles is estimated using arithmetic mean. (Note that if there are N vehicles observed, then there will be N – 1 headways that will be measure.)


For longer observation period:

Therefore, the average time headway and flow rate are related as follows:

Example 3.4 During morning peak hour, the average headway of UP-Katipunan jeepneys is estimated at 5 minutes. If the passenger demand during the same period is 240, determine whether there is a need to increase the number of jeepney units (or shorten the headway) for this route. Assume that passenger demand is evenly distributed within that period and the average load/occupancy is 14 passengers per jeepney. (Note: This assumption may not necessarily be true do to fluctuation of passenger demand and variability of passenger occupancy.)

Solution: From equation 3.5, the number of jeepneys per hour is

 

 



 

  

With an average load of 14 passengers per jeepney, the total number of passengers that can take a ride is 12 x 14 = 168 passengers Since the demand during morning peak hour is 240 passengers, it can be said that there is a need to increase the number of jeepney units during peak period.

Spacing Spacing is the distance between two vehicles measure from the front bumper of a vehicle to that of another. Similar to the estimation of time headway, if there are n vehicles within a


given road section L, the sum of (n -1) spacing s i will be almost equal to L. Average spacing, therefore, may be computed as the inverse of density.





(3.6)



Example 3.5 During heavy traffic congestion, it was observed that the average spacing of vehicles in queue in the innermost lane of EDSA is 6.5 m. Determine the jam density of stopped vehicles.

Solution: From equation 3.6, the jam density is

 

 

  

Time occupancy Another useful measure of traffic flow is time occupancy. It can only be measure, however, if a detector is installed at a specific point on the carriageway. It is defined as the total time of a detector is occupied divided by the total time of observation. Figure 3.4 shows how a vehicle is detected using ultrasonic detector.

Figure 3.4 Vehicle detection using ultrasonic detector


Assuming that n vehicles were observed during the total time of observation T, the time occupancy Ot is given by

(3.7) th

where ti is the detection time of the i vehicle.

3.3 RELATIONSHIP OF FLOW, SPEED, AND DENSITY

A relationship exists among the three most important traffic variables: flow rate, space mean speed, and density. A dimensional analysis of the units will show that flow rate (veh/hr) is simply the product of density (veh/km) and space mean speed (km/hr), or

q = k x us

(3.8)

As mentioned earlier, density is the most difficult variable to measure. It can be obtained indirectly using this relation.

3.3.1 Observed Relations It is oftentimes useful to determine the relation between any two variables. Surveys at the South Luzon Expressway were conducted. Scattered plots of the data are shown in figure 3.5.

a. speed-density relation


b. volume-density relation

c. speed-volume relation Source of Data: Tagapolot, 1997

Figure 3.5 Volume-speed-density relations for the inner lane of South Luzon Expressway

3.3.2 Empirical Relations Speed-density relation Figure 3.5 shows that as density increases, speed decreases. Looking at the scatter plot, it is easy to visualize that a linear relation may be assumed between the two variables. (Note that other highways may exhibit a trend other than linear.) This linear relation was first investigated by Greenshield (Gerlough and Huber 1975). To describe this line, the density corresponding to zero speed will be called jam density (k j) and the speed corresponding to zero density will be called free flow speed (uf ). Theoretically, density is not zero since at least one vehicle must be present.


The equation of the line that gives the relation between speed and density can be easily determined by ratio and proportion

        

(3.9)

Example 3.6 Data on density and speed were obtained from a four-line, two-way rural highway (in one direction only): Density, veh/km 75 15 142 100

Speed, kph 45 85 10 30

Determine the relation between density and speed.

Solution: A common way of analyzing relation of two variables is through linear regression. The so-called best fit line represents the data points with the least error. A scatter diagram of the data points would show that a linear equation may be well suited for the analysis.


The regression line takes the form u = a + bk where

u – speed k – density a, b – constants to be determined

The constants a and b are determined using the following formulas. (The reader is advised to refer to any statistics books for the derivation of these formulas. See And and Tang 1975.)

The correlation coefficient r is given by:

where


are the variances of u and k, respectively. The two variables will have a very good correlation if the absolute value of r is close to 1.0. To perform the regression analysis, it is convenient to prepare the table as shown:

This is almost close to -1.0, which means that the correlation between the two variables is very high. Therefore the regression line is u = a + bk = 91.96 – 0.5959 k The negative sign confirms that as density increases, speed de creases.


Example 3.7 Using the results of the previous example, determine the free flow speed and jam density.

Solution: The density-speed relation obtained from the previous ex ample is u = 91.96 – 0.5959 k Free flow speed occurs when density k = 0. uf = 91.96 – 0.5959 (0) = 91.96 kph Jam density occurs when speed u = 0. 0 = 91.96 – 0.5959 K j or K j = 91.96 / 0.5959 = 154.32 veh/km

Volume-density relation Substituting equation 3.9 to the general relation (equation 3.8): (3.10)

This equation expresses the relation of q and k as parabolic. this can be drawn as shown:

Due to the symmetry of the figure, it can be said that the maximum flow qmax occurs when the density has a value k m equal to half of jam density k j. However, when the relation


cannot be easily identified, it is useful to differentiate the function and equate to zero to get the value of k m corresponding to maximum flow, as follows:

Volume-speed relation From equation 3.9, it can also be shown that (3.11)

Substituting this in equation 3.8 gives a parabolic relation between q and us:

(3.12)

This relation is illustrated below:

Again, it can be shown that maximum flow qmax occurs at seed um equal to half of the free flow speed uf . Therefore, the value of the maximum flow, also called capacity, is


Going back to the speed-density relation qmax, is shown to be the shaded area of the rectangle.

Example 3.8 In the previous example, determine the capacity of the rural highway in one direction. Solution: As already shown, the density-speed relation can be modeled by a straight line, The formula for qmax can be used to compute for the capacity.

3.4 CAPACITY AND LEVEL OF SERVICE

Capacity is defined as the maximum hourly rate at which persons or vehicles can reasonably be expected to transverse a point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic, and control conditions. On the other hand, level of service (LOS) is a qualitative description of how a certain facility is performing. Traffic engineers rely on capacity and level of service analyses to determine the width and number of lanes when planning for new facilities or when expanding existing facilities that are already experiencing congestion problems.


The Philippine Highway Planning Manual (PHPM) developed by Planning Service of the DPWH provides a methodology to carry out the process of such analysis. The LOS concept uses qualitative measures that characterize operational conditions within a traffic stream and perception of these conditions b y motorists and passengers. Six levels of service are defined for each type of facility and are given letter designations from A to F, with A representing the best operating conditions and F the worst. Each level of service represents a range of operating conditions and is defined by quantitative factors known as measures of effectiveness. In the PHPM method, LOS are defined based on the computed volume and capacity ratio and the space mean speed of the traffic flow. The volume referred to is the hourly demand volume. This method was similar to the Highway Capacity Manual (HCM) method of 1965. The latest HCM now considers density as the main variable in determining LOS. Nevertheless, both methods gives the same description of each level of service as shown in table 3.1.


Table 3.1 Levels of service


Under the PHPM method, these levels of service correspond to the areas shown in figure 3.6

Figure 3.6 Levels of service

Figure 3.6 is actually the same diagram as the volume-speed relation but with the horizontal axis normalized by dividing volume by the capacity Table 3.2 shows the value of volume-capacity ratio for each LOS.

Table 3.2 Volume-capacity ratio and LOS


In the current US Highway Capacity Manual , the different measures of effectiveness that most appropriately describe the LOS for different types of facility are shown in table 3.3.

Table 3.3 Measure of effectiveness for different highway types

Example 3.9 From the example of section 3.3, if traffic volume in the same direction where capacity was estimated was 2,050 vehicles per hour at a particular period, determine the level of service of the highway (in that direction).

Solution: The capacity computed in the previous example was qmax = 3,547.82 vehicles per hour. The volume-capacity ratio is  



 

 

Comparing this volume-capacity ratio with the values provided in table 3.2, the LOS is C.

3.5 HYDRODYNAMIC AND KINEMATIC MODELS OF TRAFFIC

Using fluid flow analogy, models are used to describe traffic flow will be developed in this section. Consider two points on a one-way road assumed to be homogeneous:


Let Ni – number of cars passing station i during time interval Δt. qi – flow (volume) passing station i during Δt. Δx – distance between stations Δt – duration of simultaneous counting at stations 1 and 2.

By definition,

(3.13)

Suppose N1 > N2 (means traffic is building up).

(3.14)

Let Δk: increase in density between stations1 and 2 during period Δt. Then

or equating equation 3.14 and equation 3.15:

(3.16)


If the medium is considered continuous and finite elements are allowed to become infinitesimal:

(3.17)

This is well known as the continuity equation. With q = uk

Recall that u = f (k) Expanding:

(3.18)

Applying chain rule:

(3.19)

Substituting equation 3.19 in equation 3.18:

(3.20)

Analogous to fluid flow, the equation of motion expressing the acceleration of traffic stream at a given place and time is given by

(3.21)


where c is a constant of proportionality.

If

is positive, then traffic flow has a tendency to slow down.

On the other hand, if

is negative, the traffic flow tends to go faster.

Let us generalize the fluid-flow analogy equation:

(3.22)

With speed u = f (x, t).

Combining the above with the general equation,

but

using equation 3.19:

Dividing the above equation by u’:

(3.23)


This has exactly the same form as equation 3.20. Equating equations 3.20 and 3.23:

Considering that u and k always have an inverse relationship, the negative sign is added on the right side of the equation.

(3.24)

We can now consider some specific models, the first of which is the Greenshield’s model (n = 1).


This gives the u-k relationship for Greenshield’s model:

(3.25)

Two more models can be easily identified:

Greenshield’s model:

n = -1

Parabolic model:

n=0

Table 3.4 summarizes the different macroscopic model depending on the value of n:

Table 3.4 Macroscopic models

3.6 QUEUING THEORY

Queuing at a gasoline station or at the toll gate, falling in line to transact business at the bank or just to get a movie pass, queuing at a busy parking lot, jet planes waiting before being


given the signal to land or takeoff – these are everyday occurrences that would surely tests one’s patience. Queuing analysis provides ways of assessing the impacts of these activities by knowing the magnitude of vehicular delay and the extent of queue propagated. The models that will be discussed in this section are derived based on some assumptions related to arrival and departure patterns, and the prevailing queue discipline. Consider the system shown in figure 3.7.

Figure 3.7 Queuing system

The input is normally characterized by some form of arrival pattern usually given by its arrival distribution. The output generally depends on the queue discipline and the service mechanism at the service station. The most common type of queue discipline s the so-called FIFO or first-in first-out, i.e., the first one that arrives at the service station gets served first and therefore the first to leave the system as well. (Another type of queue discipline, which has limited application to traffic flow, is the so-called LIFO or last-on first-out. Typical examples of this discipline are the following: the last rider of an elevator normally gets out first; the last document piled on top gets signed first – not a recommended practice!) Service mechanism refers to the manner customers are served at the station. For example, a toll booth that charges a single fee, accepts only a fixed amount, and does not give back any change will have a fairly uniform service rate compared to a booth that charges variable toll fees and gives back change up to the last centavo. Kendall’s notation is popularly used to describe a queuing system. It takes the form A / B / C (n)


where A – represents the input or arrival pattern’ B – represents the service mechanism C – represents the number of services n – represents the limit of the queue or users

Arrivals and departure may either follow a random or deterministic pattern. Markov (M) is used for random processes while Deterministic (D) is used for processes that are characterized by regular or constant arrivals or departures. Typical examples of these processes are: M / M / 1 (∞) – random arrival and departure (service rate); one or single server; infinite queue (no limit) M / M / N (∞) – random arrival and departure; N or multiple servers; infinite queue D / D / 1 (∞) – regular arrival; regular service rate or departure; single server; limit of queue is 100. A combination of Markov and deterministic processes, say M / D / 1 may also be used.

3.6.1 D / D / 1 Queuing Due to the regularity of both arrivals and departures, it is more convenient to analyze a D/D/1 queuing system graphically. Arrivals and departures are easily represented by straight lines with the slopes corresponding to their rates.

Example 3.10 Consider a temporary single lane o-ramp/entrance to the expressway. While the entrance is open 24 hours, a fixed toll fee of P10 is charged from 7AM to 9AM as a form of congestion pricing. On the average, a vehicle is served for 7.5 seconds during which the teller receives the fee and gives back the charge, The flow rate is 600 vehicles/hour during the first 25 minutes after which, it is reduced to 360 vehicles/hour and remains constant for the next hours as shown in figure 3.8.


Figure 3.8 Graphical representation of D/D/1 queuing for example 3.10

Consider time t reckoned from 7AM. The total number of vehicles that have arrived and departed are estimated:

Queue is expected to dissipate at the intersection of the two lines. At this point, the total number of arrivals will be equal to the total number of departures. 250 + 6 x (t-25) = 8 t or t = 50 min Therefore queue dissipated at about 7:50 AM. After which, no queue is expected to propagate since the departure rate (8 veh/min) is already higher than the arrival rate (veh/min). The total number of vehicles delayed is 8 x t = 8 x 50 = 400 veh The longest queue occurs at t = 25 min with a value of (10-8) x t = 2 x 25 = 50 veh The total vehicular delay is estimated from the area of the triangle, i.e., area between arrival and departure curves.


Total vehicular delay = ½ x 50 veh x 25 min + ½ x 50 veh x (50-25) min = 1250 veh/min The average delay per vehicle is 1250/400 = 3.12 min/veh

3.6.2 M/D/1 Queuing The M/D/1 queuing system assumes that the arrivals of vehicles follow a negative exponential distribution, a probability distribution characterized by randomness. Departure is assumed to be regular as in D/D/1. The reader is advised to refer to other books on queuing theory for the derivation of the formulas.

Note that if ρ < 1 then λ < µ, which means that the system is stable. Otherwise, queue becomes longer and longer (unstable condition). Basic formulas for M/D/1:

(3.26)

(3.27)

(3.28)

Example 3.11 At the exit of a toll gate with a single booth, vehicles arrive at random at a rate of 20 vehicles per minute. The service has an average rate of 22 vehicles per minute. Estimate the following: a. average length of queue formed at the toll gate


b. average waiting time of vehicles c. average time vehicles spent in the system

Solution: Arrival rate is λ = 20 vehicles/minute. Service rate is µ = 22 vehicles/minute. Utilization factor is ρ = 0.909.

(Note that although ρ <1, the condition may start to become unstable.)

3.6.3 M/M/1 Queuing The M/M/1 queuing system assumes negative exponential for both arrival and departure distributions.


Basic formulas for M/M/1:

(3.29)

(3.30)

(3.31)

Example 3.12 Consider the same problem in example 3.11. However, due to variable toll fees, the service is also random with an average rate of 22 vehicles per minute.

Solution:


It may be observed that with a stochastic service rate, estimates for M/M/1 are almost twice that of the M/D/1.

3.6.4 M/M/N Queuing When there is more than one server, such as in toll gate shown in figure 3.9, an arriving vehicle will be able to proceed to a vacant gate, if available.

Figure 3.9 Toll plaza with N gates

Otherwise, the driver may have to wait in queue if all gates are full. Again the arrivals are 







assumed with a rate of λ and the service rate per server is µ. ρ is still defined as . However,

is

defined as the utilization factor. 

For M/M/N, the value of ρ may be greater than 1 but must be less than 1 for stable 

condition. Basic formulas for M/M/N: a. Average length of queue

(3.32)

where

(3.33)


b. Average waiting time

(3.34)

c. Average time spent in the system

(3.35)

Exercise 3.13 If the operator of the toll road in the previous example wants to improve the current condition at the toll plaza, determine the new queue characteristics if the number of toll booths is increased to 2.

Solution: The number of servers N = 2. From the previous example, ρ = 0.909 and the utilization factor is ρ/N = 0.909/2 =0.454. The probability of having no vehicles in the system is computed first using equation 3.33


Increasing the number of toll booths to 2 will greatly improve the operation of the toll plaza.

3.7 SHOCK WAVE

Stalled vehicles, traffic accidents, parades, or any other temporal activities will cause abnormal traffic flow and will definitely reduce the capacity of the roadway. Such occurrences lead to long queues extending several kilometers that can only be dissipated long after the obstruction has been removed. Analysis of this type of problem is done using shock wave theory. Shock wave is simply the motion or propagation of a change in density and flow. Consider two flow regions A and B as shown in figure 3.10. Region A has prevailing flow described by speed u1 and density k 1 while flow in region B has a speed u2 and k 2.


Figure 3.10 Two flows with different properties

The following notations will be used for the derivation of formulas for shock wave: S – shock wave; vertical line separating regions A and B. uw – speed of shock wave S; positive if line S moves toward the positive x direction. u1 and u2 – space mean speeds in regions A and B, respectively. ur1 – speed of vehicles in region A relative to the moving line S; ur1 = (u1 – uw) ur2 – speed of vehicles in region B relative to the moving line S; ur2 = (u2 – uw) Let N be the number of vehicles crossing the line S at time t: N = (Ur1k 1) x t = (U r2k 2) x t Substituting the values of Ur1 and Ur2: (u1 – uw) k 1 = (u2 – uw) k 2 or u2 k 2 - u1k 1 = uw (k 2 – k 2) with q1 = k 1u1 and q2 = k 2u2:

 

   

(3.36)

This is the general equation for the speed of the shock wave u w. On a q-k curve, equation 3.36 is represented by the slope of the line connecting points 1 and 2 as shown in figure 3.11.


Figure 3.11 Representation of shock wave in q-k diagram

Example 3.14 During the last election campaign, a 500 m convoy of presidential and senatorial candidates belonging to F4 Party was moving at a pace of 5 kph along Pan-Philippine Highway. At the tail of the convoy, it was joined by a traffic flow with estimated volume of 1,800 veh/hr and density of 30 veh/km. Since it was impossible to overtake, a platoon density of 200 veh/km was formed. If the head of the convoy exited the highway after moving 7 km: a. Draw approximately the q-k diagram showing shock waves. b. Estimate the length of queue after the convoy has cleared the road. c. Estimate how long it would take to disperse the platoon queue.

(Assume capacity of the road = 2400 veh/jr at density = 80 veh/km; jam density os at 150 veh/km)


Solution: a. q-k diagram

b. Length of queue after the convoy has cleared the road.

Duration of 7 km trip (Note convoy has length of 0.5 km, thus end of queue clears after covering 7.5 km) = 7.5 / 5 = 1.5 hrs Maximum length of queue: 1.5 x 9.706 = 14.559 km

c. Time to disperse the platoon queue.


PROBLEMS

1. Passenger car unit (PCU) is used to convert mixed type of traffic into a single unit, which is the car. If PCU values are given for the different types of vehicles.

Determine the volume in pcu per hour for the given traffic data.

2. Five cars are traveling at constant speeds 24, 31, 28, 35, 19 kph, respectively, in a uniform section og highway 4 km long. Determine the time mean and space mean speeds. Which one is higher, time mean speed or space mean speed? Can you think of the reason why this is so? 3. Using a surveillance camera, 15 vehicles were observed within 350 m section of the innermost lane of the North Luzon Expressway. Determine the traffic density of the innermost lane. Also, estimate the average spacing of these vehicles. 4. To measure the spot speed of vehicles on a certain accident-prone location along MacArthur Highway, a trap length equal to 40 m long was set. The times in seconds clocked by an observer for 24 vehicles were:

Determine the spot speed or time mean speed. If the maximum speed limit at the location was set at 60 kph, determine the percentage of drivers violating the regulation? (Note: This is just an illustrative problem; more data are actually needed for this kind of analysis.)


5. On the average, a UP Ikot jeepney arrives every 2.2 minutes at a certain jeepney stop during peak hours. If the average load factor observed is 16 passengers per jeepney, estimate the total passengers carried in 1 hour. 6. The spacing of moving traffic in queue can be modeled by (in meters) where u is the traffic speed in kilometers per hour. Determine the maximum traffic flow and the speed and density at which this occurs. 7. Estimate the capacity of a given highway with density equal to 110 veh/km during jam condition and with a speed of 80 kph during free glow condition. Assume a linear relation between density and speed. 8. In a problem 7, if the density at one point in time is 90 veh/km, determine the corresponding speed. 9. Before major rehabilitation, the daily traffic volumes of the section along the South Luzon Expressway and national highway going to Batangas are shown in the table below. Determine the level of service of each section. Assume peak hour factor of 8 percent and a directional distribution of 60 percent. Make other assumption based on your observations/experience.

10. Derive the relation between time occupancy and density for each of the following cases: a. Ultrasonic detector (the detector emits an ultrasonic wave toward the pavement at a single point.)


b. Inductance loop detector (the detector is a magnetic wire loop embedded on the pavement with dimensions d x d meters). 11. A square inductance loop detector embedded in the pavement has a dimension of w meters on one side. This detector is used to estimate time occupancy Ot of vehicles over observation time T. If the average length of vehicles is l meters, determine the density k in terms of Ot. 12. Data obtained from a survey are as follows:

Perform regression analysis on speed-density relation and estimate the maximum flow or capacity. 13. If the relation between speed and density is given by -bk

u = ae

where a and b are constants. Determine the maximum flow. 14. Estimate the capacity of a road with the given seed-density relation: u = 90 – 90 – 1.125 1.125 k where u is in kph and k in veh/km. 15. A one-way road is found to have a capacity of 2000 cars/hr. If a traffic enforcer says that the traffic volume there is only 150 cars/hr, can you conclude that the traffic condition is not congested? Why or why not? Illustrate using diagram. 16. Derive all the elements of the macroscopic models given in table 2.4. 17. Consider a truck terminal with 2 platforms. Empty trucks’ trucks’ arrival follows Poisson process with average arrival rate of 2 trucks in an hour. Each platform can load goods with a service time of 28 minutes/truck (negative exponentially distributed). Assume that an arriving truck can use any available platform.


Analyze the problem using queuing theory. If you are the operator of the truck terminal, will you retain the 2 platforms, reduce it to 1 , or increase it to at least 3? 18. A provincial bus terminal operating 24 hours has 5 bays. On a daily basis, about 200 buses arrive at the terminal. If no bay is available, the arriving bus has to wait outside, thereby causing problems for through traffic. On the average, a bus leaves a bay every hour. Assess the present operation of the bus terminal. Furthermore, due to the projected increase in passenger demand, it is expected that the arrivals of buses will increase by 5 buses every year. Determine the required number of bus bays for better operation of the terminal for the next 10 years. 19. Traffic flow at the rate of 1200 veh/hr and density of 20 veh/km joined the tail of 400 m long Santacruzan procession Santacruzan procession moving at a pace of 3 kph. Since it was impossible to pass, a platoon density of 190 veh/km was formed. The head of the procession was expected ti exit the road after moving 1 km. (Capacity of the road = 2000 veh/hr at density = 45 veh/km; jam density at 200 veh/km). a. Draw approximately the q-k diagram to show the computation of shock wave. b. Estimate the length of queue after Santacruzan procession Santacruzan procession has cleared the road. c. Estimate how long it would take to disperse the platoon queue. 20. A public school holds its flag ceremonies every Monday from 7:00 AM to 7:15 AM. During the singing of the national anthem, which lasts for about 2 minutes, all drivers stop in front of the school as an act of respect. Determine the characteristics of the shock waves formed by this activity. Estimate the time required fo r the traffic flow to be back to normal.


21. Traffic flow on a single lane is moving with a free flow speed of 40 kph and density of 50 veh/km. This flow is stopped for 45 seconds at an intersection controlled by signals. Assume jam density density of of 250 veh/km. a. What would be the speed and direction of the stopping wave? b. What would be the length of cars stopped?

REFERENCES



Ang, Alfredo H.S., and Wilson H. Tang. 1975. Prob 1975. Probabil ability ity concept conceptss in engine engineeri ering ng pla planni nning ng and design. Vol. 1. New York: John Wiley & Sons. Son s.



Gerlough, Daniel L., and Matthew J. Huber. 1975. Me 1975. Meic ic flow flow the theory ory:: A monog monogra raph ph.. Special Report 165, Transportati Transportation on Research Research Board, National Research Council.



Planning Service, Ministry of Public Works and Highways. 1982. The Philippine highway planning plannin g manual. Vol. 2. Manila.



Tagapolot, Humprey Ariel P. 1997. Effects of lane blockage on the traffic flow behavior at expressway. expressw ay. MA thesis, College of Engineering, Engineering, University of the Philippines Philip pines Diliman.



Transportation Research Board. 1965. Highway 1965. Highway capacity cap acity manual. Nati manual. National onal Resear Research ch Council. Council. 2000. Highway 2000. Highway capacity manual. manual. National National Research Research Council.

4: TRAFFIC STUDIES

4.1 INTRODUCTION

Several variables have been discussed in the previous chapter. They provide the basic information necessary for meaningful planning, design, and analysis of highways and other road transportation infrastructure. Equally important is the manner these data are obtained or collected in the field. Traffic studies generally involve time and may entail much cost. It is therefore necessary to plan carefully all data collection efforts. This chapter discusses the methodology for conducting surveys, how they are processed and analyzed.

4.2 VOLUME STUDIES

Traffic volume is the most basic data needed for any traffic studies. Volume studies are conducted to obtain factual information on the number of vehicles and/or persons that pass at a specified point on the highway system. The resulting volume data are expressed in relation to time.

4.2.1 Types of Volume

a. Annual traffic is used for determining annual travel, estimating expected highway user revenue, computing accident rates. b. Annual average daily traffic (AADT) is used for measuring the present demand for service by the road, programming capital improvements. c. Hourly traffic is used for evaluating capacity deficiencies, geometric design or improvement of streets and intersections. d. Short-term count is used to estimate maximum flow rate and determine the characteristics of peak hour volumes.

4: TRAFFIC STUDIES

4.2.2

Tapes of Data Collected

a. Mid-block Mid-block counts are used for preparing preparing traffic traffic flow maps and determining determi ning trends. trend s. b. Directional counts are used for determining directional distribution for capacity analysis, signal timing, justifying traffic control, etc. c. Turning movement or intersection counts are used for signal timing, designing or improving geometry of intersection, planning turning prohibition, analyzing high accident intersections. d. Classification counts are used for determining modal split, estimating effects of heavy vehicles vehicles on capacity, determining determining correction factors for automatic counts. co unts. e. Cordon counts are used to determine the number of vehicles and/or persons entering and leaving an enclosed area. f. Screen line counts are classified counts taken at some points along a line that bisects a given area.

4.2.3 Time of Study

The time and duration of a traffic volume study depends on the type and application of the data to be gathered. Some of the typical counts are as follows: a. Twenty-four-hour counts from midnight to midnight b. Sixteen-hour counts from 6 AM to 10 PM to represent most of daily flow, including evening traffic c. Twelve-hour counts from 6 AM to 6 PM to cover most of daytime traffic d. Peak period counts from 7 AM to 9 AM, 5 PM to 7 PM, or other time intervals corresponding to very high level of traffic volume e. Short counts of about one hour or less with intervals of 5-15 minutes to analyze characteristics of peak hours.

Abnormal conditions are usually avoided unless the purpose is to obtain information concerning those conditions. These would include a. special occasions such as public holidays or fiestas

4: TRAFFIC STUDIES

b. days with abnormal weather conditions c. strikes or demonstrations.

4.2.4 Me thod th od s

A. By tallying This is the simplest and sometimes most practical in the absence of any mechanical or automatic counting device. Tally sheets are used to record the number of vehicles. The method may be used when traffic volume is generally low or when observing a particular turning movement whose volume is relatively low. A filled up sample form is shown in figure 4.1.

Figure 4.1 From used for manual tally

B. Using manual counters A manual counter is a mechanical device useful when volume is high. Counters may he of single or multiple type.

C. Using automatic counters When traffic count of very long duration is required, automatic counters through the use of detectors may be used. The simplest type of an automatic counter is a

4: TRAFFIC STUDIES

pneumatic tube laid transversely across the road . A co un ter is ac tuat ed when tires pa ss ov er th e tube . Mo re sophisticated detectors make use of ultrasonic waves or inductance loops.

D. Using video cameras Video cameras may be used to take footage of the traffic flow. Counts may then be carried out later through either tally or manual method while watching the video. Automatic counts can also be performed using equipment and commercially available software for vehicle tracking. The cost, however, of such equipment is still very prohibitive.

4.2.5 Presentation of Traffic Volumes

Traffic volume summaries may be presented in ways that should be easily understood by the readers, some of which are as follows: a. Variations

Figure 4.2 Sample daily variation of traffic volume within a week

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b. Flow Maps

Figure 4.3 Sample flow map of annual daily traffic

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c. Intersection Diagram

Figure 4.4 Sample intersection flow summary

4.2.6 AADT and ADT

The annual average daily traffic or AADT has been a common measure of daily traffic at a given location. At a given point along a particular highway, it is estimated as the total volume counted over one year divided by the number of days in the year, or AADT = sum of all vehicles passing the site in a year / 365

(4.1)

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Doing counts throughout the year is a tedious task if done manually. Automatic detectors are therefore used to do the count manually. As previously mentioned, the simplest type of detector to perform automatic counting is the pneumatic tube laid transversely on the highway. A counter connected to the tube is actuated by the passage of the wheels. It is the vehicles axles that are actually counted. There is, therefore, a need to conduct a separate traffic volume survey over a shorter period considering the different mix of traffic. This will then be used to calibrate the counts obtained from the detectors. Another measure of daily traffic is the average daily traffic or ADT. This is obtained by conducting traffic volume counts over a number of days at least 2 days and less than 365 days. The Department of Public Works and Highways is programming the conduct of such counts in such a way at to have good estimates of AADT for all national highways by applying some seasonal factors. Daily volumes, AADT in particular, are useful in highway planning or in prioritizing some maintenance or repairs of roads. However, they cannot be used along for design or operational analysis purposes because in many cases, the traffic volume varies greatly throughout the day.

4.3 SPOT SPEED STUDIES

The objectives of conducting spot speed studies are to a. determine the range and magnitude of speeds as a basis for formulating the design standards, b. establish maximum and minimum speed limits, c. determine the need for posting advisory speed signs, d. determine the need for school zone protection, and e. evaluate the performance of a geometric improvement or traffic control device through a “before-and-after” study.

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4.3.1 Time of Study

The period during which speeds are measured depends on the purpose of the study. Abnormal conditions such as adverse weather condition or unusually heavy traffic condition should be avoided. The duration of the study should be around one hour. Short study period will often lead to bias towards faster vehicles.

4.3.2 Sized of Samples

Normally, the speeds of at least 50 vehicles – preferably 100 – should be measured. To th

cover all representative vehicles, measurement of every n vehicle may be applied. In this way, bias that may be attributed to the following may be avoided: a. Selecting mostly leaders of the platoon b. Selecting mostly one particular type of vehicle c. Selecting faster vehicles

4.3.3 Methods

A number of methods for conducting spot speed studies are available. The lack of equipment does not pose any problem as long as the procedure is done systematically.

Radar speed meter When such instrument is available, the use of radar is very convenient way of conducting spot speed studies. The radar is positioned at the edge of the roadway at an angle of 15 degrees with the centreline and is directed toward the incoming vehicles. Radar maybe difficult to use when volume of traffic is high. Radar meters are often used by police authorities for apprehending over speeding drivers.

Manual method A very useful and less expensive way of conducting spot speed studies is called the “trap length” method. In this method, two lines, 30-50 m apart, are drawn transversely on the

4: TRAFFIC STUDIES

pavement. A stopwatch is then used to measure the “travel time” of the vehicle within the “trap”. The length of the trap is divided by the travel time estimate the speed. The observer must be well trained in order to reduce error attributed to parallax, a common error in most visual methods of conducting surveys. An alternative to conducting spot speed directly in the field is to take video of the traffic flow and watch it at a later time in the office. Markings on the pavement may be drawn before the video is taken. Another way is to put markers on the roadside that will help draw the “trap” on the TV screen or monitor.

4.3.4 Analysis and Presentation of Spot Speeds

Spot speed data are usually summarized in a frequency table. Data are normally grouped together in predetermined class intervals, and distributions are calculated. There are no strict rules in deciding the number of speed class intervals. However, the Sturgess formula

       

(4.2)

where k – number of class intervals n – total number of observations may serve as a guide in determining the initial number of class intervals. It may be further refined later. Preferably, the value of the midclass of each interval should be an integer or a whole number to help simplify computations.

Example 4.1 Table 4.1 shows how spot speed data are summarized. For the estimation of the mean and standard deviation, the data were grouped. The last two columns were added to facilitate computation of these parameters.

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Table 4.1 Spot speed summary for grouped data

The mean and variance were obtained using the following formulas for grouped data:

Mean,

(4.3)

Variance,

(4.4)

Standard deviation is the square root of the variance, √  .

The graph of the spot speed frequency distribution is shown in figure 4.5. It may be observed that spot speed distribution would likely follow a no rmal distribution.

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Figure 4.5 Spot speed frequency histogram

4.4 TRAVEL TIME AND DELAY STUDIES

Travel time studies normally give information on the performance of a particular roadway. Independent measurements of stops and their observed reasons may also be included to give information on delays.

4.4.1 Methods

Test car technique The method makes use of a test vehicle that is driven over the road section under study. The driver is instructed to travel at a speed that in his opinion is representative of the speed of the traffic stream. The form used for travel time and dela y study is shown in figure 4.6

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Figure 4.6 Sample travel time and delay field sheet

Example 4.2 A single test run along the national highway in Calamba, Laguna, is shown in table 4.2. Determine the average travel speed and draw the sectional travel time and speed diagrams.

Solution: The travel speed of each section is computed in the last column of the table The two diagrams represent distance-time and distance-speed diagrams, respectively.

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Table 4.2 Summary of travel time and delay survey along national highways in Calamba, Laguna

Licensed plate method When details on delay are not important, the license plate method may be conducted. The method basically consists of observing and recording license plates of vehicles and time of arrivals at two points or more on the road where the vehicles are expected to pass. The plate numbers are then matched manually, or encoded in the computer for automatic processing. It may be convenient to divide the time of observation into 5- or 10-minute intervals. Within each interval the license plates of vehicles passing the point of observation are recorded. If traffic volume is heavy, it may be very difficult to observe and record the complete license plate number. It may be more practical to just record the first letter and the last three digits.

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Figure 4.7 Time-distance diagram for Example 4.2

Figure 4.8 Travel speed-distance diagram for Example 4.2

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Example 4.3 Table 4.3 below show filled up field sheets for a route origin-destination survey using license plate method. Determine the travel times of those vehicles that were observed at both survey stations.

Solution: It may be observed that the plate numbers XKR748, TNU210, and 888888 were recorded in both forms. The corresponding travel times are 55 minutes, 50 minutes, and 45 minutes, respectively. Table 4.3 Sample filled up sheets for license plate method

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Moving observer method One of the most common survey methods for obtaining information on traffic volume. speed, and density of a given section of road is the so-called moving observer method. Developed by the Transport Road Research Laboratory in the United Kingdom, the method consists of one or two test cars traveling back and forth within the section. A team is composed preferably of at least two observers and one timer. The survey is very easy to conduct------one observer counts the number of vehicles moving in the opposite direction; another observer counts the number of vehicles that pass them as well as the number of vehicles that they pass; the timer notes down the time it takes to traverse the section. Figure 4.9 shows the time's-distance diagram, which will help in the formulation of the necessary equations to be used. The lines represent the trajectories of the vehicles in the direction shown. The moving observer vehicle is represented by the bold line. It is shown negotiating a U-turn after traversing the road section L.

Figure 4.9 Diagram showing how the moving observer travels back and fourth

Consider the road section L as shown. Suppose we are to obtain information on volume, speed, and density of the traffic flow from a to b.

Let

tw – travel time of test car when travelling with th e stream ta – travel time of test car when travelling against the stream t – total travel time = tw + ta

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m – number of vehicles met by the test car when traveling against the stream o – number of vehicles overtaking the test car when travelling with the stream p = number of vehicles passed by the test car when traveling with the stream

If we consider, for example, the number of vehicles n that is supposed to be counted at pint a. Then n will be equal to the number of vehicles m met by the test car when travelling against the stream less the number of vehicles p passed by the test car plus the number of vehicles o overtaking the test car.

n= m – p + o

(4.5)

Note that p vehicles must be deducted because the test car will meet them again when travelling back. Over the total time of observation t, the flow rate q therefore is:



 

  

(4.6)

To determine the traffic stream’s speed or space mean speed, it is necessary to know the average travel time of the traffic flow over the road section L. If the test car is travelling at speed faster than the average speed of the traffic stream, then there will be more passed vehicles than overtaking vehicles, giving a net of (p-o) vehicles (figure 4.10). Also, if the test car is travelling at speed slower than the average speed of the stream, then there will be more overtaking vehicles than overtaken vehicles, a net of (o-p) vehicles. In other words, the test car is supposed to be travelling at average speed when the net of overtaken and overtaking vehicles is zero. Another way of stating this is, when one vehicle overtakes the test car, it must also overtake one vehicle but not necessarily the one that has overtaken it.

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Figure 4.10 Test car travelling at average speed must have a net of (o – p) = 0.

Assuming that flow rate is the same within any time period, then,

(4.7) or

(4.8) in case of the test car travelling at speed slower than the average speed. Also,

(4.9) or

(4.10) in case of the test car travelling at speed faster than the average speed.

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It can be seen that in both cases, the same result is obtained for the value of the average travel time. Hence, in general,

(4.11) The average speed of the traffic stream over the section L is obtained:

(4.12) Finally, the density k may be computed as a derived quantity:

(4.13) If information on both directions is desired, two teams are utilized to do the same routine of going back and forth transversing the road section L. In conducting this survey, the ease in negotiating a U-turn is a major factor that would affect the accuracy of the survey results. The road section must be as homogeneous as possible, e.g., uniform road width all throughout the section; entry and exit points should be minimal; very few jeepneys or buses stopping for loading and unloading, etc. In practice, at least six round trips are performed to achieve good results.

Example 4.4 A survey on a 1.2 km highway was conducted using the moving observer method. During the morning peak hour, the test car was able to complete 6 runs for each direction. Determine the traffic volume, average traffic speed, and density. Eastbound trips:

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Westbound trips:

Solution: The average 6 runs is computed for each direction.

The traffic volumes are computed using equation 4.6:

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The average travel times are computed using equation 4.11:

With L = 1.2 km, the average speeds are computed using equation 4.12:

Finally, the densities are computed from equation 4.13:

PROBLEMS

1. Draw the intersection diagram for the given traffic volume summary of a T-intersection:

4: TRAFFIC STUDIES

2. The following spot speed data (in kph) were obtained from a city road.

Perform the following: a. Group the data and summarize the tabular form b. Determine the mean and standard deviation. c. Draw frequency histogram th

th

3. In the determination of speed limits for roads, the `5 and 85 percentile speeds are usually considered as the minimum and the maximum speed limits, respectively. For problem 2, draw the cumulative frequency diagram and determine the minimum and maximum speed limits. 4. While taking measurements using the moving observer method, a test vehicle covered a 1.5 km section in 1.5 minutes going against traffic and 2.5 minutes going with traffic. Given that the traffic flow was 800 vehicles/hour and that the test vehicle passed 10 more vehicles than passed it when going with traffic, find a. the number of vehicles encountered by the test vehicle while moving against traffic, b. the speed of the traffic being measured, and c. the density of the traffic stream.

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5. A survey using moving observer method was conducted to obtain information on volume, speed, and density. Five observations were made at different times of the day and the results of the survey for a particular direction of flow are as follows:

Estimate the capacity of the highway section for the given direction of flow. 6. Develop a survey methodology to determine the volumes and average travel speeds of traffic hat are using the bypass and the national highways. Naturally, you would try to minimize the number of surveyors so as to minimize the survey cost.

REFERENCES



ALMEC Corporation. 1999. Metro Manila Urban Transportation Integration Study. Final Report.



Institute of Transportation Engineers. 2000. Manual of transportation engineering studies. Washington, D.C.: ITE.



th

Pline, James L., ed. 1992. Traffic engineering handbook. 4 ed. Institute of Transportaion Engineers and Prentice Hall.

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

Sigua, R., and C. Montalbo Jr. 2005. Calamba City of Public Transport Terminal Study Draft Report, December.



Transporting Training Cneter. 1983. Course notes on transportation and traffic technology. Quezon City: University of the Philippines.

5: INTERSECTION DESIGN AND CONTROL

5.1 INTRODUCTION

Intersections play an important role in any network system. They are the points where traffic flow converges and where direction of travel changes. Intersections may be categorized according to shape, type of structure, and type of operation.

Shape This refers to the configuration of the intersection and would depend largely on the number of legs. Carefully planned and properly designed road networks often lead to intersections with simpler shape having lesser number of legs. Some of the most commonly observed intersection configuration is the following:

a. Three-leg: T or Y

b. Four-leg: normal crossing, oblique, or skewed/staggered

c. Multileg: intersections with more than four legs


d. Rotary or roundabout

Type of structure Most of the intersections are either designed as at-grade intersection or grade separation such as flyovers or interchanges. Almost all intersections are initially designed at-grade and are planned to be grade-separated in the future to cope with high traffic volume. The type of grade separation depends largely on the extend of improvement it would provide in terms of easing congestion or reducing traffic accidents.

Type of operation Rules and regulations applied to a given intersection depend largely on the type of control which is in operation at that intersection. The main objective is to simplify traffic flow. This is often achieved by reducing the number of conflicts of vehicles. An intersection operates as unchannelized or channelized, and unsignalized or signalized. Channelization often leads to simplified movements of vehicles as it leads drivers to one conflict at a time. On the other hand, signalization greatly crossing conflicts at the intersection area.

5.2 BASIC INETRSECTION DESIGN PRINCIPLES

When designing or improving an intersection, it is very important to follow some basic principles to avoid costly mistakes that lead to lack of the intersection’s capacity or to its being accident-prone. a. The maximum number of legs should be four. It has been shown that the number of conflicts increases exponentially as the number of intersection legs increases.


b. Staggered intersections should be avoided. Due to proximity of the two side roads, inadequate length of storage lane for left vehicles often causes blockage of the through traffic. c. Main traffic flow should be near straight as possible. Sharp turns, such as left and right turns, cause unnecessary reduction in traffic speeds.

d. Roads should not intersect at a small angle. Oblique intersections pose potential hazards and cause high severity of accidents due to the almost head-to-head collision of vehicles. An angle of 60 degrees must be considered as the minimum.

e. Two intersections should be as far as possible from each other. In addition to the reason cited in (2), adequate weaving sections may not be provided. As a rule of thumb, the distance between the two intersections must be

distance = design speed (kph) x number of lanes x 2

For instance, if the prevailing speed is 30 kph and three are four lanes in one direction, the distance between the two intersections must be at least 30 x 4 x 2 = 240 m.


5.3 INTERSECTION DESIGN ELEMENTS

Turning geometry The principal purpose of an intersection is to provide change in the direction of travel. As a vehicle approaches an intersection, the driver has to decide whether to go straight or to turn to left or right. For turning movements, a number of turning geometries may be considered, the most direct of which is highly preferred. Configurations of turning geometries are shown below:

a. Direct

b. Semidirect

c. Indirect


These types of turning movements may be found as elements of the interchanges shown below:

The different elements of an intersection are shown in figure 5.1. The adequacy in design of each element must be carefully checked, considering traffic flow and availability of right of way.


For the left turn storage bay, the recommended length is = 2 x no. of left turners in one cycle x spacing in queue. The spacing in queue may range from 6.0 m to 7.0 m, depending on the type of vehicles using the intersection. A factor of 2 is used to take into account randomness of traffic flow. The number of lanes for through, right, and left turn vehicles would depend on traffic volume, saturation flow rates, a simple circular curve may be adequate for the design of the intersection corners and the turning roadway. However, simple curve may not be enough for large intersections. The most common type of geometry for these intersections is the threecentered curve as shown in figure 5.2.

Figure 5.2 Three-centered curve

5.4 METHODS OF CONTROL OF INTERSECTIONS

Conflicts often occur at intersections. The more the number of legs an intersection has, the more the number of conflicts it has. Figure 5.3 shows the number of conflicts of three-leg and four-leg intersections.


Figure 5.3 Conflict diagrams for three-leg and four leg intersections

Conflicts may be classified as merging, diverging, or crossing conflicts. Table 5.1 gives a summary of these conflicts. The total number increases exponentially with the number of legs of the intersection. Most of the problems at intersections, like congestion and accidents, are caused by crossing conflicts.

Table 5.1 Types and number of conflicts

Depending on the traffic volume using the intersection and the severity of conflicts, intersection control may fall under any of the following categories: a. Unsignalized b. Signalized c. Grade separation


5.4.1 Unsignalized Intersection When two minor roads intersect, traffic may be assumed to arrive at any approach of the intersection in random fashion. In this case, signals may not be necessary but some of control must be employed to ensure safety. The simplest form of control is to have no control at all. At least, there are no visible reminders such as signs or markings posted in the vicinity of the intersection. There is actually a rule for minor intersections where there is no clearly defined priority. The so-called right-of-way rule governs. This rule states that when two vehicles arrive at the same time at the intersection, the vehicle on the right has the priority. This rule must be understood by all drivers and it does not depend on the size of the vehicle! There is no such thing as “right of weight”. In the case of intersections where priority is clearly defined – a major road crossing a minor road, for instance – the traffic on the minor road has to depend on available gaps at the major road to be able to cross or turn. For this kind of intersections, reasonable controls for unsignalized intersections may be done through the use of traffic signs such as YIELD or STOP sign. The use of YIELD sign is to establish or strengthen legal superiority of one traffic flow over another where most traffic on all legs is able to proceed through without a full stop. With the use of STOP sign, two-way control, or four-way stop control may be implemented. In a twoway stop control, the major approaches without STOP signs have complete priority over the minor approaches with STOP signs. In the four-way stop control, all approaches have equal priority, Studies indicate that four-way stop control works the best advantage of traffic when flows on the two cross streets are approximately equal. In a simulation study of four-way stop control by Wright, it has been found out that the percentages of right, left and through movements has a little effect on delay and queue lengths. This may be due to the fact that fourway stop control offers flexibility, i.e., the driver is given the opportunity to use his own judgement in deciding what movements are possible at a given instant.

5.4.2 Roundabout or Rotary This is another form of unsignalized intersection that works best when the number of turning vehicles is almost equal to the number of through vehicles. In a roundabout, all vehicles move counter clockwise in one-way fashion. Movement is characterized by merging at very


small angles, weaving, and diverging when leaving the intersection. When traffic signals’ cost proved to be costly, roundabout is a good alternative.

Figure 5.4 Roundabout (all vehicles move in one-way fashion) (Photo taken by author.)

5.4.3 U-Turn Slots The U-turn scheme has been implemented at several intersections within Metro Manila for a number of years now. Operation at U-turn slots is very similar to that of a roundabout except that it favors a particular road, which is assumed to be the major road.

Figure 5.5 A U-turn slot in Quezon City (Photo taken by author.)


5.4.4 Signalized Intersection The control of traffic intersections by traffic signals is done by separation in time, i.e., conflicts between opposing or merging streams are prevented by giving the right of way to a given direction. Section 5.7 provides an introduction to traffic signal control. Consider a four-leg intersection with all movements allowed. Figure 5.6 shows the conflict diagrams for the different types of intersections discussed previously.

Figure 5.6 Conflict diagrams for different types of control for a four-leg intersections


Table 5.2 shows a comparison in terms of number of conflicts and the applicable type of control or regulation for these four types of intersection.

Table 5.2 Comparison of types of control for a four-leg intersection

5.4.5 Grade Separation Grade separation eliminates the problematic crossing conflicts of the different movements of vehicles. Flyover/overpass, underpass, or full-blown interchanges are some of the examples of grade separation. Some of these grade separations or interchanges are shown in figure 5.7. They provide the safest and most efficient method of control but definitely the most costly, and sometimes unaesthetic.


Figure 5.7 Grade separation or interchanges

5.5 ANALYSIS OF UNSIGNALIZED INTERSECTIONS

A large number of intersections all over the country are still without traffic signals. It is therefore necessary to have a means of analysis of the performance of this type of intersection so as to find appropriate measures to minimized congestion and reduce the occurrence of traffic accidents. The method presented in this section was the basis of the method discussed in the US Highway Capacity Manual with some modifications. In our case, it may be better to introduce the original method. As new researches on the topic are conducted, modifications may be done to suit local conditions. The method calculates the maximum flow in any given minor road traffic stream. It is them compared with the existing traffic flow to estimate the reserve capacity. The probable delay and level of service are determined based on this reserve capacity.


Consider the four-leg intersection below. Minor movements are movements coming from the side road or minor road. In addition, the left turn movements from the major road are also m=considered minor. But in terms of hierarchy, these left turn movements have higher priority than the movements coming from the minor road.

The method requires that the traffic movements be dealt with in the following order: a. Right turns into the major road b. Left turns off the major road c. Traffic crossing the major road d. Left turns into the major road

5.5.1 Structure of Major Road Traffic Table 5.3 shows the different major road traffic streams, which have to be considered when analyzing a particular minor road flow. Note that for the traffic turning right from the major road (m1), which actually does not have direct conflict with the minor flow being considered, half of its volume is considered as inhibiting effect. If this inhibiting effect is shown to be absent through actual observation of the condition, M1 may be totally omitted.


Table 5.3 Major road traffic streams

5.5.2 Critical Gap The source of capacity of the minor road flows is the available gaps between major road flows. The critical gap used to describe the minimum gaps needed by drivers of minor road vehicles. Values of critical gaps are given in table 5.4 for different vehicle maneuvres, speed limits, and highway type.

5.5.3 Capacity In the estimation of capacity of the minor road flow, the basic capacity is initially determined. Based on the major road flows given by Mh, and values of critical gap tg, the value of the basic capacity Mno is read from the graph shown in figure 5.8.


Table 5.4 Critical gap tg for passenger cars, sec.

Figure 5.8 Basic capacity of minor road flow


The basic capacity is the maximum minor road flow, assuming that the following conditions are true: a. The traffic on the major road Mh does not block the major road. b. A turning lane is provided for the exclusive use of the minor road traffic stream.

If these conditions are not met, correction factors have to be implied based on the following considerations: a. Congestion on the major road If a traffic stream turning off the major road becomes congested and thus interferes with the minor road traffic, then the basic capacity is reduced. A p-value is obtained from figure 5.9 and is applied as a reduction factor. The p-value defines the probability that this minor road traffic stream remains unaffected. The ration of the actual flow and the capacity of the same flow is initially used to determine the p-value.

Figue 5.9 Reducation factor due to possible congestion of movement of major road


b. Shared lanes Shared lanes on the minor road approach are lanes in which two or more movements are confine in the same lane. When corners of the intersection have a large turning radius, the effect of shared lanes may be minimal or may be ignored since minor vehicles can stop side by side at the edge of the major road. The capacity of the share lane can be determined using the equation

(5.1) where

Mn - capacity of all streams using the shared lane Mna, Mnb, Mnc - capacity of individual streams a, b, b - contribution of the individual streams to the total volume using the shared lane.

5.5.4 Passenger Car Equivalents Since the calculated capacity is in pcu/hr, the existing flow has to be converted to the same unit. Table 5.5 may be used for this purpose.

Table 5.5 PCU values of different vehicle types


5.5.5 Reserve Capacity The difference between the existing flow and capacity is termed as reserve capacity. The magnitude of delay and level of service are directly related to this reserve capacity. Table 5.6 is used for assessment purposes. Overall evaluation or generalization may have to be done after assessing each minor traffic flow.

Table 5.6 Reserve capacity

Example 5.1 Consider the channelized T-intersection with the minor road controlled by YIELD sign. There is no prevailing speed limit. Evaluate the performance of the unsignalized intersection.


Solution: Following the logical order of analysis as suggested: a. Right turn into major road

b. Left turn off major road


c. Left turn into major road

Overall evaluation: The left turn traffic into major road experiences very long delay. There are no problems with the other minor flow. The left turn off major road is not likely to block the through traffic.

Example 5.2 Evaluate the unsignalized intersection with the two minor road approaches controlled by STOP signs. The traffic volumes shown are in vehicles per hour (vph). There is no prevailing speed limit.


Solution: Due to symmetry of traffic volume data, only the analysis of the minor road approach C will be shown. The same condition is expected in approach D. a. Right turn into major road

b. Left turn off major road


c. Crossing major road

d. Left turn into major road


Overall evaluation: the intersection requires improvement. Traffic signals and geometric improvement (channelization) may be necessary.

5.6 ANALYSIS AND DESIGN OF ROUNDABOUTS OR ROTONDAS

The elements of the roundabout are shown in figure 5.10. Roundabout with large central island are known to operate better as they provide ample weaving sections that normally dictate the capacity of the intersection.

Figure 5.10 Some design elements of a roundabout


For the analysis and design of roundabouts, British practice will be discussed in this section (Salter 1976(. The focus is the capacity of the weaving section, which is given by the equation

(5.2) where

w – the width of the weaving section in meters e – the average width of entries to the weaving section in meters;



  

l – the length of the weaving section

These variables are defined in figure 5.11, which shows a typical weaving section

Figure 5.11 Weaving section


The capacity formula is valid under the following conditions, although there is no reason to believe that the formula does not hold if any variable lies a little outside the values given:

The design of roundabouts is usually done by trial and error. Weaving width and length are assumed and then checked for adequacy of capacity. As roundabouts have a tendency to lock when overloaded, it is important that they have adequate reserve capacity.

Example 5.3 Consider the Y-junction with the given traffic volume to be designed as a roundabout.

Table 5.7 Types and number of conflicts


It is usually convenient to draw the intersection diagram as follows:

With the traffic volume superimposed, section AB is the weaving section with a critical volume of 1,300 vehicles per hour. Assuming the following:

The capacity of AB section is calculated:


The computing for the reserve capacity:

The other sections (AC and BC) may be designed with the same parameters, this providing large reserve capacity.

5.7 TRAFFIC SIGNAL CONTROL

For intersections with relatively low traffic volumes typically found in rural and suburban areas, traffic may be assumed to arrive at the intersection in random fashion. Likewise, the same randomness of arrivals may be observed where spacing between intersections is of considerable distance. In these situations, signals may not be necessary and the intersection has to be controlled by traffic signs as discussed in the previous chapter. The control of traffic intersections by traffic signals is done by separation in time, i.e., conflicts between opposing or merging streams are prevented by giving the right of way to a given direction. This separation in time is termed as signal phasing. And it can be seen that the more the number of conflicts, the more the number of phasing needed. However, in some cases as in a major street-minor street intersection, or in approaches where left-turning volume is relatively low, a separate phasing for the minor flow may not be necessary. The number of phases employed at any intersection must be kept to a minimum, compatible with safety because with every phase added, there is a corresponding additional loss of green time, which eventually leads to increased intersection delay.

5.7.1 Types of Signals Nowadays, many types of traffic signals are being used to control traffic flow. Depending on the distance and influence of one or more signals over the other, the intersections may be classified as isolated, coordinated or area controlled.


Isolated A particular intersection may be considered isolated if arrivals of vehicles at its approach are random. Consider the traffic flow at the two signalized intersections A and B are shown in figure 5.12. Supposing a queue formed in A proceeds toward intersection B. If the queue has dispersed and vehicles arrive at random at B, then B may be considered as an isolated intersection. Naturally, this will happen only when distance between the two intersections is far or when traffic volume is relatively low. In highly built up areas such as the city or town centers, it is unlikely to have this kind of intersection.

Figure 5.12 Two intersection distant apart (Isolated intersections may be controlled either pre-time or actuated.)

Pre-time signal Pre-time or fixed time signals work best when there is not much fluctuation in traffic flow. The pre-time signal controller may be of a single or multiprogram type of controller. The single-program controller makes use of one set of signal parameters to control traffic flow throughout the day or during the period when the signal is in operation. On the other hand, the multiprogram type makes use of a number of sets parameters. This offers greater flexibility and may be able to cope with the fluctuating demand within the day (figure 5.13). Nowadays, a controller with dive or more programs is not uncommon.

Figure 5.13 Programming per-time signal control


The Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) cites the advantages of pre-time control: a. Consistent starting time and duration of intervals of pre-time control facilities coordination with adjacent traffic signals especially when they are on two or more intersecting streets or in a grid system. This coordination may permit progressive movement and a degree of speed control through a system of several well-spaced traffic signals. Pre-time control provides more precise coordination that allows maximum efficiency in the operation of two or more very closely spaced intersections operating under the capacity conditions, when the timing relationship between intersections is critical. b. Pre-time controllers are not dependent for proper operation on the movement of approaching vehicles past detectors. Thus the operation of the controller is not adversely affected by conditions preventing normal movement past a detector such as stopped vehicle or construction work within the area. c. Pre-time control may be acceptable than traffic-actuated control in areas where large and fairly consistent pedestrians volume are present, and where confusion may occur as to the operation of pedestrian push buttons. d. Generally the installed cost of pre-time equipment is less than that of traffic-actuated equipment, and the former is simpler and more easily maintained.

Traffic-actuated For isolated intersections where randomness of arrivals is expected, traffic actuated type of signal control is appropriate (figure 5.14). In this system, detectors are located only on the approaches of the minor road. With this set up, continuous green time may be given to the major road traffic flow. Right of way is given to the minor road only when demand is detected. In case of two roads where no clear priority is given to any direction, the fully actuated type of control is sometimes utilized. In this scheme, all approaches are provided with detectors. When the interval of time between vehicles crossing the detector becomes greater than the last unit extension period, the right of way is transferred to the other directions. When there is heavy volume of traffic in a particular direction, successive demand for extension period may


happen and this will lead to continuous green indication. Hence, a present maximum green period is necessary to limit the length of the green period. It can be expected that when traffic demand is heavy in all approaches, green period may always reach the maximum resulting in an almost fixed-time operation.

Figure 5.14 Types of traffic-actuated signals

In a general, a minimum green period or shortest period of right of way is given to any phase. This minimum green period is long enough to clear the vehicles waiting between location of the detector and the stop line, and it may be extended for as long as continuous demand for the right of way exists. Such extension periods are individually and not cumulatively set. Figure 5.15 shows how traffic-actuated control works.


Figure 5.15 Green time extensions for traffic-actuated control

THE MUTCD gives the special advantages of traffic-actuated control, which include the following: a. Traffic-actuated control may provide maximum efficiency at intersections where fluctuations in traffic cannot be anticipated and programmed for with pre-time control. b. Traffic-actuated control may provide maximum efficiency at complex intersections where one or more movements are sporadic or subject to variation in volume. c. Traffic-actuated control will usually provide maximum efficiency at intersections of a major street and a minor street vehicular or pedestrian traffic, and also by restricting such interruptions to the minimum time required. d. Traffic-actuated control may provide maximum efficiency at intersections unfavourably located within progressive pre-time systems, where interruptions of major street traffic are undesirable and must be held to a minimum in frequency and duration. e. Traffic-actuated control may provide the advantages of continuous stop-and-go operation without unnecessary delay to traffic on the major street, whereas isolated pre-time signals are sometimes switched to flashing operation during periods of light traffic. f.

Traffic-actuated control is particularly applicable at locations where traffic signal control is warranted for only brief periods during the day.

g. Traffic-actuated control tends to reduce any hazard associated with the arbitrary stopping of vehicles.


Coordinated Where randomness can no longer be ensured and there is a need for continuous movement over an arterial, coordination or synchronization of the timing of the signals in series is required. A number of methods are used to achieve this. This methods are discussed at the last section of this chapter. It is also possible that within an arterial, subgroups consisting of a number of intersections may be developed (figure 5.16). Each subgroup is treated independently from another subgroup.

Figure 5.16 Subgrouping of intersections for efficient control

Area traffic method In urban centers, links (road sections) and nodes (intersections) often form a network (figure 5.17). Optimization techniques have been developed to cope with such network. Nowadays, sophisticated software run by powerful computers are sued. Examples of these are the SCTAS, SCOOT, etc.

Figure 5.17 Road network in urban centers suited for area traffic control


At present, the Sydney Coordinated Adaptive Traffic System (SCATS), a dynamic control system is installed in Metro Cebu and some parts of Metro Manila. In Metro Cebu, it was claimed to have improved the traffic situation in the city. It was also believed that the system has helped inculcate discipline among the drivers, commuters, and pedestrians. SCATS and SCOOT (Split Cycle Offset Optimization Techniques) are considered as third-generation system, in which the signal timings are free to evolve in response to detected traffic volumes and queues. While demand-responsive systems are more expensive both to install and to operate compared with fixed-time systems, when operated in the correct environment they usually achieve benefits that compensate for their capital expenditure within the first few years of operation. In the SCAT system, small subareas of up to ten intersections share a common cycle length, which can be altered by p to 6 seconds once per cycle according to the degree of saturation of that subarea. It can strategically combine certain subareas for varying lengths of time to improve on overall network performance. It draws its data from stop line detectors. Each subarea has five offset plans. These internal offsets between adjacent intersections within a subarea are predetermined as part of the input database. Internal offsets can vary according to the current cycle time and an input parameter known as the progressive speed factor, which governs the percentage change in offset. There are also five external offset plans for the purpose of “marrying” or merging two subareas. These plans are selected by an algorithm that may be used to select internal offsets. When two adjacent subareas are married, the common cycle time for the combined area is the larger cycle time of the two separate subareas before linkage.

5.7.2 Data Requirements for Traffic Signal Setting In planning for phase pattern and for the determination of appropriate timing of the signals, a number of data are required: a. Traffic Volume – must include all types of vehicles (including nonmotorized: bicycles, pedicabs, etc); directional b. Pedestrians flows – movement of pedestrians in all directions c. Passenger car unit values (PCU) – PCU equivalent of the different types of vehicles d. Saturation flow rates – maximum flow rate occurring at the stop line once traffic initially in queue is given green time indication


e. Physical characteristics of the road – number of legs; width of approaches; number of lanes; gradient. Consider the flow of a single queue of vehicles once signal indication turns to green as shown in figure 5.18. At the start of green, it can be observed that the lead vehicle will take a second or two to react. It will be after two or three vehicles crossing the stop line when the traffic flow will be at maximum rate. This brings about what is called starting loss. In the diagram, the starting loss is estimated as the time from the actual start of green up to the point where the line representing the maximum rate crosses the horizontal axis. The maximum flow rate that corresponds to minimum headway is also known as the saturation flow rate. The value of saturation flow rate depends on a number of factors: vehicle mix, condition of the pavement, geometric characteristics of the road (width of the lan e, gradient), direction of movement, etc.

5.7.3 Phase Phasing is a process by which right of way is given to particular movements in a logical manner with the primary purpose of minimizing the number of conflicts. The number of conflicts at an intersection depends largely on the geometry of the intersection and turning prohibition. It may be observed that as the number of legs of the intersection increases, the number of conflicts increases exponentially.

Figure 5.18 Saturation flow rate determination


In planning for the appropriate phase pattern for a particular intersection, the major factors o be considered are the traffic volume and any turning regulation/prohibition. Oftentimes, it is the left turn movement that gives the problem at an intersection as it complicates and increases the number of the required phases. Nevertheless, the basic principle is to minimize the number of phases commensurate with safety. Given the geometry of the intersection and a set of traffic volume, there are actually many possibilities of developing phase patterns. The role of the traffic engineer is to find out the most appropriate one to meet the requirements of meeting the traffic demand and providing safety to all road users. Some of the most common phase patterns are shown in figure 5.19:

a. Two-phase system

b. Three-phase system Figure 5.19 Typical phase patterns

Again, in developing appropriate phase patterns, each phase should not combine any major conflicting movements. In the two-phase system shown in figure 5.19a, for example, the through and the right turn traffic may have some conflict. However, this is normally of diverging type and may not pose a problem as long as the vehicles stay on their respective lanes. Phase 1, for example, does not allow a left turn movement. This is the situation when this movement is prohibited in the intersection or when the number of left turn vehicles is so small that it does not warrant a left turn phase. However, when left turn movement becomes problematic, it is often


necessary to provide a separate left turn phase as shown in figure 5.19b. Here are some basic guidelines when planning for the phase patterns. a. Start with the most problematic/heavy movement. Add movements one at a time and see to it that they are not in conflict with the previous movements. b. The number of phases must not exceed the number of legs of the intersection. (Note: patterns with overlapping movements will be discussed in a separate section. They are not really counted as phases.) c. Rearrange the phase patterns so as to follow a logical order.

5.7.4 Lost Times In the previous section, it has been said that the number of phases must be minimized commensurate with safety. The major reason for this is that as the number of phases increases, the amount of lost time also increases. The lost time is composed of the starting loss and the allred period. In figure 5.20, it can be observed that for every phase, there is a corresponding starting loss and all-red period. The generally accepted value of starting loss is 2 seconds. The amount of all-red periods depends on the size of the intersection. Together with the yellow or amber period, they compose the clearance interval or intergreen period. With the yellow or amber having a value of 3 seconds, the all-red period has to be long enough for the last vehicle crossing the road to clear safely.

Figure 5.20 Lost times consisting of starting loss and all-red period


5.7.5 Cycle A cycle is one complete indication of green, yellow and red. Its length is constant for a pre-time or fixed time signal. It varies for traffic-actuated signals depending on traffic demand. The fundamental relation between intersection delay and cycle length is shown in figure 5.21.

Figure 5.21 Cycle and delay relation (Co provides the minimum delay.)

It can be seen that using either a long or short cycle will lead to long delay, with very short cycle giving worse results. The objective of signal timing is to minimized delay. There are other objective functions – travel speed, fuel consumption, emissions, etc.- but they are all related to delay. Reducing delay would lead to better speed, fuel savings, and lesser emissions. The cycle corresponding to least intersection delay is termed as the optimum cycle length. Webster’s formula is widely used to estimate this cycle length. The equation is given by

 

 

(5.3)

where L – total lost time Y – sum of y-values The consumption of cycle will be illustrated by an example.

Example 5.4 Consider the traffic volumes and saturation flow rates for the different movement:


Compute for the optimum cycle time. (Use yellow = 3 sec; All red = 3 sec; Starting loss = 2 sec)

Solution: Analyzing the different movements, directions, and traffic volumes, a two-phase signal may be appropriate.

For all movements, the y-values are computed.

For phase 1, the critical y-value is 0.325 while for phase 2, the critical y-value is 0.517. This gives Y-value = 0.325 + 0.517 = 0.842 For this two-phase signal, the loss time L is: L = 2 x starting loss + 2 x all-red = 2 x 2 + 2 x 2 = 8 sec. From equation 5.1, the optimum cycle length is:

 

 



 

     

(The cycle length is normally rounded off to multiples of 5 or 10.)


5.7.6 Allocation 5.7.6 Allocation of Green Times After the cycle length is computed, the total green time has to be allocated to the different movements or phases. This is normally achieved by dividing it in proportion to the y-values. For a particular phase, i, for example, its green time is estimated as follows:

(5.4)

Example 5.5 Consider the data in the previous example, allocate the green time to phases 1 and 2.

Solution: The computed optimum cycle is 110 sec and the total lost time is 8 sec. This results to total usable or effective green g:

5.7.7 Capacity 5.7.7 Capacity of Movement or Approach Given the amount of green time allocated to an approach or movement and its saturation flow rate, the capacity of such approach or movement can be estimated as follows: 

     

where s – saturation saturation flow rate g – effective effective green C – cycle cycle length

(5.5)


Example 5.6 In the previous example, determine the capacity of the south approach. Solution: The south approach has a saturation flow rate s = 1,800 pcu/hr of green time Its effective green is equal to the effective green of phase 2 (g2 = 63 sec) Therefore:

           

 

   

 

     

5.7.8 Estimation 5.7.8 Estimation of Delay The equation for the optimum cycle length was actually derived by minimizing the delay function obtained by Webster. We bster. Webster’s formula formula for delay consists of three terms. The first term is the major component of the delay equation. It can be easily obtained by considering the area if the triangle in figure 5.22. This is actually based on a D/D/1 queuing where both arrival (q) and departure (s) patterns are assumed regular. The second term based on Allsop was obtained by assuming an additional queue interposed between the arriving traffic and the signal. The last term is a correction factor obtained from simulation.

(5.6)

The first term is the dominant term in the formula representing 90-95 percent of the total average delay. From figure 5.22, this component of delay will be derived.

Figure 5.22 Delay representation per cycle


Assuming it takes to to dissipate the queue after the start of green:

The total delay per cycle D is equal to the area of the triangle in figure 5.22.

(5.8)

Therefore, the average delay per vehicle per cycle is

(5.9)

Example 5.7 Using equation 5.9, estimate the average delay per vehicle per cycle of movement 3.

Solution: Movement 3 has a y-value equal to 0.325. Its effective green is 39 sec. Therefore, its effective red is r = c – c – g g1 = 100 – 100 – 39 39 = 71 sec Using equation 5.9, the average delay is


5.7.9 Timing Diagram After all the signal parameters have been computed, it is better to produce the timing diagram where all the numerical values are displayed. This is later applied to the signal controller. Figure 5.23 shows a sample timing diagram for a two-phase signal system.

Figure 5.23 Timing diagram for a two-phase system

Example 5.8 Draw the timing diagram for the problem in example 5.4

Solution: The timing diagram is normally drawn using the actual green (not the effective green). Actual green is computed as follows: actual green + yellow = effective green + starting loss (Note: yellow is considered usable and is part of th e effective green) Since yellow = 3 sec and starting loss = 2 sec actual green = effective green – green – 1 1 For phase 1: actual green, G1 = 39 – 39 – 1 1 = 38 sec For phase 2: actual green, G2 = 63 – 63 – 1 1 = 62 sec The timing diagram is shown with the different components in seconds.


5.7.10 Intersection 5.7.10 Intersection Degree of Congestion Although the Y-value gives the indication whether to continue with the computation or not, the degree of congestion X, is often used as the measure of the performance of the intersection. For a given approach or movement, the degree of congestion of that approach or movement is the ratio of the demand over capacity. Let xi be the degree of congestion of a particular movement or phase. i, then

(5.10a)

On the other hand, the intersection degree of congestion X is given by

(5.10b)

It can be shown that the degree of the intersection is also the same as the degree of any movement of approach if the allocation of green is based on the proportion of y-values.

Example 5.9 Compute for the degree of congestion of the intersection described in example 5.4.

Solution:


With the cycle, Y-value and L computed previously, equation 5.10b can be used to determine the degree of congestion.

Equation 5.10a can also be used to compute for the intersection degree of congestion since green times are allocated based on the proportion of y-values. Consider movement 1 with volume = 930 pcu/hr and saturation flow rate of 1,800 pcu/hr. Based on y-value of 0.517, its green time was computed as 62.6 sec. (This was rounded off to 63 sec in the previous calculations). The degree of congestion of movement 1 based on equation 5.10a is

which is equal to the degree of congestion X.

5.7.11 Critical 5.7.11 Critical Movement Analysis When phase patterns become complex, cycle time and green times needed by the different movements may be determined using the critical movement analysis method. This is the same method used by Akcelik in his Signalized and Unsignalized Intersection Design and Research Aid (SIDRA) program and by the US Highway Capacity Manual for the design and analysis of signalized intersections. For a given combination of intersection geometry and traffic volume, a finite number of logical phase patterns may be identified. (Logical phase pattern is defined here as a phase pattern that is normally accepted in traffic engineering practice in terms of safety and driver expectation.) Let m – m – total total number of possible phase patterns th

pi – i i phase pattern The best phase pattern P that is expected to result in minimum delay is (5.11)

where Ycri is the sum of y-values of critical movements movemen ts in Pi.


Figure 5.24 shows the three typical “stages” for vehicles at a T-intersection. The corresponding critical movement diagram is shown in figure 5.25. The term “phases” is not used because of the overlapping movements (defined as movements present in more than one stage), namely: 1, 4, and 5. The cycle time and green time may be dictated by the time requirements of any of the following sets: [1, 6], [3, 5], [2, 3, 6], or [2, 4]. Each sets consists of movements that form a complete cycle. The set that gives the highest Y-value forms the critical movements. In other words: (5.12)

where n is total number of possible sets.

Figure 5.24 Three stages for a T-intersection

Figure 5.25 Critical movement diagram for the T-intersection


Example 5.10 Consider the T-intersection with given traffic data:

Compute for the optimum cycle time.

Solution: Based on the traffic flow, the phase pattern o r stages shown below may be considered:

The y-value of each movement is computed.


The y-values are superimposed in the critical movement diagram

Each of the following sets consists of movements that form a complete cycle:

Therefore, the critical movements are [2, 3, 6] with Y-value = 0.658. Since there are three major movements involved, 3 starting losses and all-red periods are expected, giving a total loss time L = 3 x (2+2) = 12 sec. The optimum cycle is computed using equation 5.4

Allocating green time will be the same as in ex ample 5.5

5.7.12 Treatment of Left Turn Traffic If left turn traffic is allowed at the intersection, three types of control may be considered: (1) without phase. (2) with fixed time left turn phase, and (3) with actuated left turn phase.

Without left turn phase As a rule, multiple phases should be avoided whenever possible because they generally require an increase in the overall cycle length. Other options may be considered; left turn bays, shorter cycle lengths, leading or lagging greens or both, and turn prohibitions. In the case of


without left turn phase, it is apparent that the left turners have to depend on the available gaps in the opposing through traffic. Given a sufficient length of left turn bay, the interaction between left turners and through traffic can be avoided. If there is no left turn bay, the left-turning vehicles are mixed with straight-ahead and right-naming vehicles (in ease of single lane) on the same approach. This may have the following effects on the traffic flow: a. Because they are delayed from turning left by other vehicles in the traffic stream, they delay straight-ahead vehicles that may be following them. b. The presence of left-turning vehicles in a particular lane tends to inhibit the use of this lane by straight-ahead vehicles. c. Those left-turning vehicles that remain in the intersection after the expiration of the green period delay the start of the next phase until they have completed their left-turning maneuver.

With fixed time left turn phase As the volume of left turn traffic increases, providing additional phase for them seems inevitable. The simplest Conn is a fixed time left turn phase. Fur any given traffic c Mimi with the signals operating under fixed time control, the duration of the cycle affects the average delay of vehicles passing through the intersection. Where the cycle time is very short, the proportion of the cycle time occupied by the lost time in the intergreen period and by starting delays is high, making the signal control inefficient and causing lengthy delays. On the other hand, when the cycle lime is considerably long, waiting vehicles will clear the stop line during the early pan of the green period and the only vehicles crossing during the latter part of the green period will be those that subsequently arrive, often at longer h eadways. As the discharge rate across the stop line is greatest when there is a queue on the approach, this also results in inefficient operation.

With traffic-actuated left turn phase For left turn traffic using traffic-actuated control. a special feature is that prior to the beginning of green for left turn, the system checks whether there is a vehicle waiting, and if found none, left turn phase is automatically skipped and the next phase begins. On the other


hand, if there is a vehicle waiting, then a minimum green period is given, and it may be extended when there is continuous demand. In the case of no exclusive left turn phase, there is usually enough time for left turners during green if there is relatively light opposing traffic. However, as opposing traffic increases, long queue may not be able to give the left turners the chance to clear the intersection through available gaps. Or even if the opposing queue ends, the green time left with random flow may be too short to clear all left turners waiting for gaps. Observation at the intersection will show that those left turners leading the queue position themselves in the center of the intersection and turn during the yellow period or the start of red interval. For high opposing traffic, this hangmen period serves as the main source of left-turning traffic. In the case of no exclusive left turn phase, it can be said that left turn capacity greatly depends on the amount of traffic opposing the left turn movement. The left-turning vehicles must cross the intersection through gaps or lags. A simple representation of this phenomenon is shown in figure 5.26. The condition on the opposing approach is shown in a, b, and c while the condition of the left turn movement is shown in d. Briefly, the opposing traffic accumulates during red period; then, at the beginning of green plus starting loss, the traffic starts to move. During normal conditions, the queue can be cleared after some of the green time has been utilized and later the flow on the opposing traffic returns to free flow condition wherein the vehicles arrive and depart from the stop line in random fashion. From this point of time on, until the green time ends, the waiting left turners assess the gaps available to them. Normally, the decision whether or not to accept the available gap is made in the following manner: a. No driver will accept a gap in the opposing stream that he or she belies will certainly lead to a collision. b. No driver gains admittance through intimidation of the opposing stream drivers.


In reality, assumption b is oftentimes violated. This may be due to the driver’s irritation caused by the length of time he or she has been delayed in the queue.

5.7.13 Left Turn Lane Length The usual approach in determining the required length of the storage lane or left turn bay has been to assume a Poisson arrival distribution and to compute the probability of the facility falling through overloading in not more than specified percentages of cycles. If the storage to he provided is for k vehicles and the mean rate of arrivals in an interval of time t is or, then

(5.13)

expresses the probability of the number of arrivals r in time t being greater than the storage capacity k. A design based on this approach assumes that the storage provided allows through traffic to proceed without interference and makes maximum use of the separate turning phase through saturation flow away from the queue o f vehicles in the storage lane.


This design approach which is frequently used by traffic engineers, generally forms the basis for the storage length recommendation given by the American Association of State Highway Officials (AASHO), which states. "At signalized intersections, the required storage length depends on the cycle length, the signal phasing arrangement and the rate of arrivals and departures of left turning vehicles. The storage length should be based on 1.5 to 2 times the avenge number of vehicles that would store per cycle, predicated on the design volume." Figure 5.27 shows a typical approach of an intersection when exclusive left turn lane is provided, say, for k, vehicles. If the (k + 1)th vehicle arrives with intention of turning left, then it has to occupy the adjacent lane, thereby blocking the through traffic in that particular lane. resulting in a considerable reduction of the saturation flow rate of the through traffic. Also, the same thing happens when there is heavy through traffic. If the through traffic queue length exceeds that of the storage length, then these vehicles will block the use of the storage lane by subsequent left-turning vehicles. And if this blocking of left-turning vehicles happens prior or during the left turn phase for that approach, then only those vehicles stored in the left turn bay can cross.

5.7.14 Effects of Left Turn Vehicles on Saturation Flow Rate Given a sufficient length of left turn bay, interaction between left turners and through traffic in the same approach is almost negligible. However, if the tail of right turn queue exceeds that of the given storage length, bother usage of the through lane adjacent to the left turn lane is

Figure 5.27 Blockage of through traffic due to inadequate length of left turn bay


stopped. If the number of lanes for one approach is 2, for example, it is reduced to 1 and the saturation flow is greatly reduced, too. When there is no exclusive left turn lane provided, the left turners greatly affect the flow of the through traffic. Also, the effect becomes considerable the more the number of left turners waiting at the approach. Once a through-bound driver sees left turners in the innermost lane, he normally keeps a way from that lane. This reduction of saturation flow rate of through traffic can also be applied to the case where there is exclusive left turn lane provided. However, the problem is a little different since blocking occurs at the junction of the left turn lane and the adjacent through lane. If left turn volume is high and the left turn lane is inadequate, it may be expected that the left turn queue will pile up until the adjacent through lane is blocked. Normally, at the start of through green, the leaders of the left turn queue proceed to the center of the intersection and wait for available gaps or leave the intersection immediately at the start of the left turn phase. This somehow eases the problem of interblocking at the junction of left turn and through lanes. After some time from the start of through green, blocking may no longer occur as the left turners at the end of the queue have proceeded to the left turn lane.

5.7.15 Coordination of Traffic Signals TO provide progressive movement of traffic flow that has to pass through a series of signalized intersections, some form of coordination has to be introduced to minimized delay. Nowadays, a number of commercial software packages are available to achieve this goal. Some of these package programs are very sophisticated and can handle large numbers of intersections within the city center. Two well-known computer software are the SCATS and the SCOOT. The SCATS is currently being used in Metro Manila and Metro Cebu. While the said software are used for coordination of more elaborate subgroups, a manual method can be used for simpler systems. Three methods that make use of simple time-distance diagram will be presented here.

Simultaneous system All signals display the same color indication this is commonly used when intersections are closely spaced, such as those along Espana.


Figure 5.28 Simultaneous system

A disadvantage of this system is that drivers tend to increase speed in order to pass as many intersections as possible.

Alternating system At any given instant of time, the driver sees intersections ahead with alternating green and red indications. This system normally works well when the intersections are far apart.

Figure 5.29 Alternating system


Progressive system The starts of green are arranged in such a way that traffic flow is uninterrupted and bandwidth is optimized. The method works well for one -way systems or when one direction of flow is given more priority over the other. For coordination, it is better to use one common cycle for all the intersections. However, if distances are irregular, some intersections may use two times the common cycle. In practice, this common cycle time is usually the cycle time of the key intersection (i.e., the intersection that normally requires the longest cycle time).

Figure 5.30 Progressive system


Example 5.11 Consider the 4 intersections 400 m apart and with the given traffic data. Determine the common cycle and the actual green times that will be used for coordination.

Each intersection will be controlled by two-phase signal in the absence of left-turning vehicles. The cycle length required for each intersection is computed. The result is summarized in the table below. Values of optimum cycle length are rounded off.


The key intersection is B, requiring the longest cycle (140 sec). For this intersection, green times are allocated as follows:

For the other intersections, the maximum actual green for other intersections depends on the minimum effective green for the side roads. This minimum effective green is computed as

(5.14)

The table shows how the required minimum green is given to the side roads so as to maximum the green along the N-S direction.

Finally, the actual green and red (in seconds) that will be used for coordinating the N-S direction are as follows:


5.7.16 Graphical Method of Coordinating Signalized Intersections The Institute of Traffic Engineers’ traffic Engineering Handbook has a graphical method of coordinating two-way systems when balance of traffic flow in both directions is desired. The step-by-step procedure is discussed: a. Preparation of the time-distance diagram. The locations of the intersections to be coordinated are drawn to scale on the horizontal axis. A construction line is drawn parallel to this axis.

b. Knowing beforehand the common cycle time and its components (effective green and red periods), a green or red is centred on the construction line. (The figure shows a red [bold line] being centred on this line.)


c. A line (line 1) with a slope corresponding to an assumed desired speed of progression is drawn. This line represents the first vehicle in platoon that will cross the first intersection.

d. Going to the next intersection, a red or a green is centered on the construction line, with the start of green very close to the initial slopping line. In the figure a green is centered on the line. The slopping line is then adjusted; this gives the new line (line 2).


e. The steps are repeated for the next intersections

f. Finally, a line is drawn parallel to line 3. This line represents the last vehicle in the platoon that will be able to cross all intersections without stopping. Lines are also drawn to represent the platoon going in the other direction. It can be seen that the method procedures a balanced flow in both directions. The final desired speed can also be estimated from the diagram (inverse of the slope of the line).

5.7.17 Offset The difference in the start of green of two signalized intersections is called the offset. Two types of definitions may be used:


a. Absolute offset This would require one of the intersections to be defined as the key intersection. Then, all offsets will be reckoned from it. O21 (read as “offset of 2 with respect to 1”) and O31 are absolute offsets when intersection 1 is defined as the key intersection in figure 5.31. b. Relative offset The offset of an intersection is defined with respect to an adjacent intersection O32 is a relative offset if intersection 1 is the key intersection.

Figure 5.31 Offset definition


PROBLEMS

1. Assuming that all movements are allowed in a five-leg intersection, determine the number of vehicular crossing, merging, and diverging conflicts. 2. Given the T-intersection below:

(The numbers shown are traffic volume in pcu/hr and saturation flow rates in pcu/hr of green time, respectively.) a. Design appropriate phasing and draw critical movement diagram. b. Determine optimum cycle. c. Draw timing diagram. d. Compute degree of congestion, X. Use all-red = 2 sec. 3. Show that the degree of congestion of any critical movement is equal to the degree of congestion of the intersection given by



 


4. For each approach of the intersection, allocate lanes for though and left and design appropriate phasing so that the degree of congestion does not exceed 0.90.

5. Two intersections are 400 m apart. Common cycle time used is a 120 sec and green time used for each intersection is 50 percent of the cycle. Determine if alternating or simultaneous system is better if progression is desired for both directions. What will be the recommended speed of progression? 6. For the given intersection, arrange the lanes (i.e., allocate lanes for through and left) of each approach and design appropriate phasing so that the degree of congestion dies not exceed 0.90.

Each approach can accommodate maximum of four lanes (through and left).


a. Calculate optimum cycle time. b. Draw timing diagram. c. Compute average delay per vehicle of approach N. 7. Given the traffic data for the one-way road shown below:

Assume the following for all intersections: All-red: 2 sec

Yellow: 3 sec

Starting loss: 2 sec

Desired progression speed: 30 kph

Coordinate the 4 intersections. Draw time-distance diagram using appropriate scale. Estimate bandwidth graphically.


8. A four-leg intersection has the traffic volume information as shown. Due to the large number of pedestrians crossing in all directions (including diagonal movements), a scramble phase (i.e., exclusive phase for pedestrians) of 20 sec after all phases are given to vehicles has been planned.

a. Determine the following: 

cycle length



green time allocation for each phase

b. Draw timing diagram. 9. A pedestrian crossing located at a mid-block has a cycle time c and is provided with effective green g. Pedestrian arrival rare is q. Saturation flow of pedestrians is considered to be very large in comparison with the arrival rate, i.e., almost all pedestrians cross at the same time at the start of green. Show that the average pedestrian delay is

REFERENCES 

Akcelik, Rahmi. 1987. Traffic signal setting: Capacity and timing analysis. Australian Road Research Board



Allsop, Richard E. 1972. Delay at a fixed time traffic signal, I: Theoretical analysis. Transportation Science 6, no.3.



Drew, Donald R. 1968. Traffic flow theory and control. McGraw-Hill Inc.




Evans, Henry K., 1950. Traffic engineering handbook. Second ed. New Haven, Connecticut: Institute of Traffic Engineers.



Federal Highway Administration. 1988. Manual on uniform traffic control devices for streets and highways. US Department of Transportation.



Japan Society of Traffic Engineers. 1988. The planning and design of at-grade intersections.



Mannering, Fred L., and Walter P. Kilareski. 1990. Princicples of highway engineering and traffic analysis. John Wiley and Sons.



Organizations for Economic Cooperation and Development (OECD). 1978. Capacity of at grade junctions. Road Research Group, Paris.



Salter, R. J. 1976. Highway traffic analysis and design. Revised edition. MacMillan Press.



Sigua, R.G. 1984. A study on control of right turn traffic at signalized intersection. Master ’s thesis, Department of Civil Engineering, University of Tokyo.



------------- 1991. An expert system for intersection design and analysis. PhD diss., Department of Civil Engineering, University of Tokyo.



Transportation Research Board. 2000. Highway capacity manual. National Research Council.



Webster, Frederick V. 1958. Traffic signal settings. Road Research Technical Paper No. 39.



Wright, Paul H. 1958. Simulation of traffic at a 4-way stop intersection. Analysis of Traffic Flow symposium. Michigan.

6: GEOMETRIC DESIGN OG HIGHWAYS

6.1 INTRODUCTION

Design of highways basically covers the geometry of the horizontal and vertical alignments, geotechnical aspects, pavement design, provision of drainage facilities and other civil structures, but the traffic engineers’ main concern is the safety aspect of the design. Several factors must be considered when designing a highway that is safe and pleasant to drive on. One of these factors is the maximum speed that certain geometry may allow. Take the horizontal curvature of the road, for instance. Without appropriate banking or superelevation, an overspeeding vehicle will likely run out of highway due to the centrifugal force that pulls it away from the road. Another is the sight distance available to the drivers. The driver must be able to see ahead in order to brake safely before hitting an object on its path. Or when negotiating an overtaking maneuver, a driver must be able to pass a slow-moving vehicle on the opposite direction. When driving at night, the headlight beam can only reach up to a certain distance. The vertical and horizontal curves must be designed so as not to cause undue reduction in speed of vehicles.

6.2 DESIGN REQUIREMENTS OF HIGHWAYS

6.2.1 Design Speed The elements of a highway are designed according to certain standards. One of these standards is the design speed, which is defined as the maximum safe speed that can be maintained over a specified section of highway when conditions are so favourable that the design features of the highway govern. It is the basis that will literally put shape to the different elements of the highway. A very smooth curve will require a very high design speed. In general, poor alignments are normally a result of wrong choice in design speed. Nowadays, however, design speeds are designated for different types of roadways, from high-speed expressways to low-speed feeder or barangay roads. The International Bank for Reconstruction and


Development (IBRD) provides guidelines on the use of appropriate design speed for various terrain and traffic volume. Table 6.1 shows this guideline.

Table 6.1 Design speed for various road classes and terrain co nditions

Whenever possible, a certain design speed must be maintained all throughout the highway. However, if terrain condition or some obstructions would not allow it, the design speed may be reduced by 10-20 kph at adjacent sections.

6.2.2 Sight Distances When designing for the alignment of the road, two types of sight distance are normally checked for adequacy: stopping sight distance (SSD) and passing sight distance (PSD).

Stopping sight distance Stopping sigh distance is the shortest distance required for a vehicle traveling at the assumed running speed to stop safely before reach ing a stationary object in its path.

Figure 6.1 Stopping sight distance


As shown in figure 6.1, SSD is composed of two distances: a. d1, distance traversed during perception plus brake reaction time. Brake reaction time consists of perception time of about 1.5 seconds and action time of 1.0 second.  





(6.1)

b. d2, distance required for stopping after brakes are applied. Short distance is required when negotiating an uphill. This is taken care of by the sign of the gradient G.

(6.2) where

v – running speed, kph t – reaction time, sec 2

g – 9.8 m/sec

f – Coefficient of friction (0.29-0.40) G – gradient (+ for uphill; - for downhill) Minimum stopping sight distance is normally computed for wet pavement condition. Table 6.2 serves as guide for computation of SSD for different design speeds. For design speeds greater than or equal to 80 kph, the running speed is taken as 85 percent of the design speed. For design speeds less than or equal to 30 kph, full value of design speed is assumed for running speed.

Table 6.2 SSD and f-values for different design speeds


Passing sight distance For two-lane highways, passing sight distance is the shortest distance required for a vehicle to safely pull out of a traffic lane, pass a vehicle traveling in the same direction, and return to the correct lane without interfering either with the overtaken vehicle or opposing traffic. Along curves, this is the length of the road that must be visibly free of obstructions in order to permit a vehicle moving at the design speed to pass a slower moving vehicle.

Figure 6.2 Passing or overtaking maneuver

As shown in figure 6.2, PSD is composed of four distances: a. d1, distance travelled during perception and reaction time and during the initial acceleration to the point on encroachment on the left lane

(6.3)

b. d2, distance travelled while overtaking vehicle occupies any part of the left lane (opposing lane)

(6.4)

c. d3, distance between the passing vehicle at the end of its maneuver and the opposing vehicle.

(6.5)


d. d4, distance traversed by an opposing vehicle for two-thirds of the time the passing vehicle occupies the left lane

(6.6)

In many cases, it is very difficult to meet the full PSD requirement. Table 6.3 shows the summary of PSD values for various design speeds. Minimum PSD is often taken as 

the sum of      . Comparing these values with SSD, the requirement for passing sight 

distance is about two to three times that of SSD. While it is absolute to provide SSD all the time, it will be very expensive to provide PSD all the time as this would mean very gentle horizontal and vertical curves. In practice, PSD should be provided in long sections of roads so that drivers will have the opportunity to overtake one -third of the time.

Table 6.3 Passing sight distance values for different design speeds

6.2.3 Minimum Radius of Curvature Smooth-flowing curves are often desired when designing highways. However, the cost of providing such curves may be too prohibitive. Existing structures or terrain may prevent the


designer from providing gentle curves. It is therefore necessary to determine the minimum radius of curvature that may be required for any given desired speed.

Figure 6.3 Vehicle negotiating a curve and forces acting on it

Considering all the forces acting on the vehicle when negotiating a horizontal curve (figure 6.3), it can be shown that the required minimum radius of curvature is given b y

(6.7)

where

v – design speed, kph, e – superelevation f – side friction

Table 6.4 provides the values of f for different design speeds. Values may be interpolated depending on the design sped used.

Table 6.4 Values of side friction f


6.3.4 Superelevation Banking or superelevation is necessary to counteract the centrifugal force that is acting on the vehicle. The value of maximum superelevation e may range from 6 percent to 12 percent. Depending on the terrain of the area where the highways will traverse, superelevation can be attained by any of the following methods (figure 6.4):

a. pavement revolved about the centreline

b. pavement revolved about the inner edge of the pavement

c. pavement revolved about the outside edge Figure 6.4 Methods of attaining superelevation


6.2.5 Design Volume th

In designing roads, the 30 highest peak hour volume has been found to be the most th

reasonable hourly volume that provides the best result (see figure 6.5). The 30 hourly volume is exceeded only twenty-nine times in a year. Beyond this value on the right, the distribution of th

hourly volumes is relatively flat. Another characteristic of this 30 hourly volume is that its value as a percentage of AADT does not vary much over the years. Depending on the type of highways, the value of K may range from 7 percent to 15 percent.

Figure 6.5 th

The 30 hourly volume

Normally, highways do not have balanced flow in both directions during peak hours. One direction is usually heavier than the other. It is therefore necessary to consider the direction of heavier flow for design. The directional distribution D, is defined as the percentage of the heavier volume over the total highway volume. This directional distribution is relevant only when designing or analyzing highways with two or more lanes in one direction. For two-lane or three-lane, two-way highways, the directional distribution are not considered. In the case of twolane, two-way highways, the heavier movement will tend to use the other direction for overtaking. For three-lane, two-way highways, the heavier movement will tend to occupy the extra third lane.


Given the AADT, the design hourly volume is computed as follows:

DDHV = AADT*K*D (for multilane highways)

(6.8)

or DHV = AADT*K (for 2-lane or 3-lane, 2-way highways)

(6.9)

where DDHV – directional design hour volume DHV – design hourly volume AADT – average annual daily traffic K – proportion of daily traffic occurring during peak hour, expressed as a decimal D – proportion of peak-hour traffic travelling in the peak direction, expressed as a decimal

6.2.6 Number of Lanes The basic task in designing highways is the determination of the number of lanes needed to meet the given design volume under a specified level of service. The procedure may follow a trial and error one. Initially the number of lanes is assumed. With this assumption, the corresponding capacity is obtained from lookup tables. If the desired level of service is known, then its corresponding volume/capacity ratio will be known. This v/c ratio should be greater than the value of the ratio of the design hourly volume over the estimated capacity. If the inequality is satisfied, then the assumed number of lanes is okay; otherwise it is modified depending on the result of the initial computations. In some cases, correction factors are applied that would reduce the capacity if some substandard values (width of lane, presence of gradient, etc.) deviate from the ideal ones. The Philippine Highway Planning Manual provides a guide on basic capacity for various road types in tables 6.5a and 6.5b.


Table 6.5a Basic capacities for highways and urban streets

For multilane highways in flat terrain, such as expressways, the lane capacities (if lane width is at least 3.5 m) are estimated as follows:

Table 6.5b Basic capacity for multilane highways

Example 6.1 A proposed highway is to be designed with adequate shoulder and clearance in a level terrain with the following: AADT = 40,000 pcu/day D% = 65% K = 9% Estimate the number of lanes that will provide LOS B.


Solution:

A six-lane, two-way highway is needed to provide LOS B.

It must be noted in the previous example that the design volume (AADT) is already given in terms of pcu. If the traffic volume provided is in mixed type, passenger car equivalent factors (PCEFs) have to be applied to obtain the volume pcu. The reader is advised to refer to the PHPM for the details of these PCEFs. Also, the procedure discussed in the PHPM (which was used in the previous example) is slightly different from the procedure in the US HCM. Both methods have capacities in pcu but in the PHPM, the design volume in mixed vehicles is converted to pcu for the calculation of v/c ration while in the US HCM, mixed vehicles are retained but the value of capacity is modified or converted to mixed vehicles by applying reduction factor due to heavy vehicles. The v/c ratio, therefore, is computed based on volume and capacity having the same unit of mixed vehicles.

6.3 HORIZONTAL ALIGNMENT

6.3.1 Circular Curve For large radius (as in railroad practice), distances along the arc are considered to be the same as along the chords. For highways, usually the distances are considered to be along the arcs, and the corresponding chord lengths are computed for measurement in the field.


Sharpness of curve The so-called sharpness of curve can be expressed by using two measurements: a. Radius, R b. Degree of curvature, D° Furthermore, two definitions are used. The arc definition is the one being followed in highway practice while the chord definition is used for railroad practice. Figure 6.6 shows the relations of R and D° for both definitions.

Figure 6.6 Arc chord definitions

Stationing In metric system, the length l used is 20 m for both arc and chord definitions. In English system, the length l used is 100 ft for both arc and chord definitions.

Example 6.2 Rewrite the following in station notations: a. Stake located 10,682.325 m from beginning b. Stake located 2,345.21 ft from beginning

Solution:


a. For metric system, Sta. 10 + 682.325 b. For English system, Sta. 23 + 45.21

Simple curve Simple curve is defined as a circular arc between two tangents (figure 6.7).

Figure 6.7 The simple curve

The following notations are used for a simple curve: PI: point of intersection of two tangents PC: point of curvature or beginning of curve PT: point of tangency or end of curve Δ: external angle of deflection between tangents T: tangent distance Lc: long chord connecting PC and PT E: external distance M: middle ordinate L: length of curve from PC to PT R: radius of curve From the geometry of the simple curve, the following elements can be derived:


T = Rtan(Δ /2)

(6.10a)

Lc= 2Rsin(Δ /2)

(6.10b)

E = R[sec(Δ /2)-1]

(6.10c)

M = R[1-cos(Δ /2)]

(6.10d)

The length of curve can be computed by ratio and proportion as follows: Using the degree of curvature D°: L/l = Δ / D°

(6.11a)

where l is one full station Or by using the radius R: L/ Δ° = 2πR/360°

(6.11b)

Example 6.3 Bushes grow near a two-lane highway circular curve with R = 160 m (measured from centreline of the highway). Minimum stopping sight distance is 150 m. Total width of pavement is 7.0 m. How near from the edge of the pavement can you allow the bushes to grow?

Solution:


Therefore, the distance of bush from edge of pavement should be at least M – 1.75 = 17.44 – 1.75 = 15.69 m in order to provide a stopping sight distance of 150 m.

Computations of stationing: The stationing of PC can be obtained by working backward; i.e., after obtaining the tangent distance T, it is deducted from the stationing of PI: Sta. PC = Sta. PI – T

(6.12)

The stationing of PT can be obtained by adding the length of curve L to the value of Sta. PC, or Sta. PT = Sta. PC + L

(6.13)

6.3.2 Compound Curve This is defined as a two-arc simple curve having its centers on the same side of the common tangent (figure 6.8).

Figure 6.8 The compound curve

The elements of a compound curve can be computed depending on the given information. If Sta. PI, Δ1, Δ2, R 1 and R 2, are known, then the solution will be the same as that of two simple


curves. The compound curve has seven important parts: T1, T2, Δ1, Δ2, R 1, R 2 and Δ. However, Δ = Δ1 + Δ2; therefore there are only six independent variables; four lengths and two angles. For rigid solution, four parts must be known, including at le ast one angle and at least two lengths.

6.3.3 Reverse Curve A reverse curve is a two-arc simple curve having its centers on opposite sides (figure 6.9). This type of curve is usually inadmissible on high-speed routes because superelevation at the point of reversal cannot be provided. Two types of reverse curve may be employed if speed is not critical. The first type is the case of having parallel tangents as shown in figure 6.9.

Figure 6.9 Reverse curve with parallel tangents

The elements of a reverse curve having parallel tangents are computed:

Usually, p is known and two or more variables must be assumed.

Example 6.4 Find the flattest common-radius reverse curve (equal radii) that can be inserted between parallel tangents 25 m apart without the distance AD exceeding 250 m.


Solution:

The other type of reverse curve is the case of nonparallel tangents as shown in figure 6.10. The solution is similar to that of compound curves.

Figure 6.10 Reverse curve with nonparallel tangents


6.3.4 Broken Back Curve A broken back curve is characterized by a short tangent between two curves in the same direction (figure 6.11). This type of curve should be avoided in design since most drivers do not expect succeeding curves to be in the same direction.

Figure 6.11 Broken back curve

Example 6.5 The broken back curve shown is to be replaced by a compound curve R 2 = 1.8 R 1.

Determine: a. new values of radii b. new values of tangents

Solution:


For the compound curve:


6.3.5 Easement Curve or Clothoid An easement curve or clothoid is usually a spiral that serves as a transition path as the vehicle enters or leaves a circular curve (figure 6.12). This type of curve follows a natural path as the driver turns the steering wheel.

Figure 6.12 Clothoid or easement curve

One property of the clothoid is that its curvature increases in proportion to the length of curve, or 1/R = kl

where

or

Rl = 1/k

(6.14)

R – radius of curve l – length of curve k – a constant

to be dimensionally correct, let A2 = 1/k (A is called the clothoid parameter). From this property:

(6.15)

where ls is the length of clothoid and R c is the radius of the circular curve. Also,

(6.16)


Hence,

(6.17)

Integrating

(6.18)

For dx and dy: (6.19) (6.20)

Substituting the expansions of cos θ and sin θ. (6.21)

(6.22)

Substituting the value of θ.

Integrating:

(6.23)

(6.24)


and

(6.25)

(6.26)

Elements of symmetrical clothoid Figure 6.13 shows a symmetrical clothoid, i.e., a c ircular curve having two clothoids at each end serving as transition paths. The two clothoids have exactly the same properties.

Figure 6.13 Symmetrical clothoid


(6.27)

For good design, ls ≈ lc. Also, clothoid is necessary when ΔR > 0.2 m Standard for the length of clothoid 1. Based on travel time (enough time for reaction) (6.28)

2. Based on rate of change of acceleration, p:

therefore:

(6.29)

Equation 6.29 is also known as the Shortt’s formula.


Range of values of p: 3

p = 0.35 ~ 0.50 m/sec for expressways 3

p = 0.60 ~ 0.75 m/sec for rural and urban highways 3. Based on aesthetics The longitudinal gradient of the superelevation runoff should not exceed 1/200.

Example 6.6 Given: design speed = 100 kph (f = 0.13) 3

p = 0.4 m/sec

Sta. PI = 5 + 105.000 Road width = 14.0 m (4-lane, 2-way) Normal crown = 1.5 % Intersection angle = 27° Design the section of highway.

Solution: Assume e = 3.5%


For the length of clothoid:

Computing for the final superelevation:

The other elements of the symmetrical clothoid can be obtained from the set of formulas given by equation 6.27.


6.7 VERTICAL ALIGNMENT

Parabolic vertical curve has been used to design the profile of highways. It has properties that make it easy for laying out the alignment of a roadway in the field.

6.4.1 Properties of Parabolic Vertical Curves a) The rate of change of grade on a vertical curve is constant.

Consider the general equation of the parabolic curve: (6.30)

where a, b, and c are constants. The first derivative dy/dx is the change of grade. The second derivative gives the rate of change of grade:

b) Tangents drawn from any two points on a vertical axis parabola always intersect midway between the points of tangency.


c) Vertical offsets from a tangent to a parabola are proportional to the squares of the distances from the point of tangency.

d) If a tangent to the parabola is drawn between the main tangents, the horizontal projection of the intercept cut off on this new tangent by the main tangents is equal to one-half of the horizontal projection of the long chord of the parabola.

6.4.2 Types of Vertical Curves There are two types of vertical curves: crest and sa g curves. Figure 6.14 shows some examples.

Figure 6.14 Types of vertical curves


6.4.3

General Equation of Vertical Curve Consider the vertical curve of length L with gradients of G1 and G2. The beginning and

end of the curve are denoted by BVC and EVC, respectively. The point of intersection of the two gradient lines is denoted by VPI. If the rectangular coordinates x and y are chosen arbitrarily as shown, then EBVC is the elevation of Sta. BVC (figure 6.15). The equation will then be:

(6.31)

Figure 6.15 Elements of vertical curve

Example 6.7 Given: Sta. VPI = 20 + 265.000; Elev. VPI = 40 m above sea level G1 = 4.5%; G2 = -3.8%; L =250 m Compute the station and elevation of the highest point on the crest vertical curve.

Solution: Using equation 6.31:


Substituting in equation 6.31:

6.4.4 Sight Distances at Vertical Curves Two sight distances have been discussed in connection with horizontal alignments: the stopping sight distance and the passing sight distance. Similarly, these two sight distances are the major factors in determining the required length of vertical curves. In measuring sight distances, the following heights are assumed in the development of standards: a. For SSD, h1 pertains to the driver ’s eye height and h2 is the height of the object (hazard) seen along the path of the vehicle.

Figure 6.16 Estimation of stopping sight distance


b. For PSD, h2 is taken as the height of the roof of the vehicle coming in the opposite direction when the first vehicle initiates its overtaking maneuver.

Figure 6.17 Estimation of passing sight distance

6.4.5 Sight Distances at Crest Vertical Curves Given the requirements for sight distances (tables 6.2 and 6.3), the required length of the crest vertical curve may be obtained by considering the following two cases: a. The sight distance is shorter than the required len gth of curve (figure 6.18).

(6.32)

Figure 6.18 Sight distance less than length of curve


b. The sight distance is longer than the required length of curve (figure 6.19).

(6.33)

Figure 6.19 Sight distance greater than length of curve In sight distance formulas, A is used as a positive number (in decimals) equal to the change in gradient from G1 to G2.

6.4.6 Sight Distances at Sag Vertical Curves Along an open highway, the length of sag vertical curves is usually based on the length of the road illuminated by the headlight beam at night. Likewise, two cases have to be considered. a. Sight distance is shorter than the required length o f curve (figure 6.20)

(6.34)

Figure 6.20 Sight distance shorter than the length of curve


b. Sight distance is longer than the required length of curve (figure 6.21)

(6.35)

Figure 6.21 Sight distance longer than length of curve

The determination of the required length of vertical curve may follow a trial-and-error method. The designer may initially assume one consistent case. If the outcome of the consumption using the specified equation is consistent with the assumption, the computed length of curve is correct. Otherwise, if the outcome contradicts the assumed case, the other equation must be used.

Example 6.8 Given: Design speed = 80 kph G1 = 2%; G2 = -2% Ss = 110 m S p = 550 m Determine the length of vertical curve. Solution:


Therefore, to satisfy SSD, the length of vertical curve must be at least 113.615 m.

The assumption is correct and the required length of curve is 1,205.179 m if PSD is to be satisfied. This is more than ten times the required length for SSD. In actual design, it is almost impossible to provide 100 percent PSD throughout the whole stretch of highway. Good design would provide PSD at least one-third of the time.


PROBLEMS

1. Determine the number of lanes required to provide LOS B (v/c = 0.21 ~ 0.50) for the following cases:

2. A two-lane, two-way highway has a volume-capacity ratio of 0.75 during peak hours. If AADT is expected to increase at a growth rate of 1 percent per annum, when should the highway operate as four-lane, two-way? Six-lane, two-way? Peak hour factor is 10 percent and directional distribution is 65 percent. (Hint: Improve the highway when volume-capacity ratio reaches 0.90.) 3. A two-lane, two-way highway has an AADT of 18,000 pcu/day. The estimated traffic growth is 4.5 percent per year. Determine the level of service at the end of 3, 5, 10 years. Will the highway be adequate after 10 years? When should the highway operate as fourlane, two-way? Six-lane, two-way? (Assume PHF = 8 percent and directional distribution of 65 percent). 4. A horizontal curve on a two-lane highway is designed with a 610 m radius, 3.5 m lanes, and 80 kph design speed. Determine the distance that must be cleared from the inside edge of the inner lane to provide sufficient stopping sight distance. (Note: Curve radius is typically reckoned from the centreline of the roadway, and driver location is assumed to be at the middle of the travelled lane.) 5. A section of two-lane highway (7 m wide) on a horizontal curve as shown has a posted speed limit of 80 kph.


A recent daytime accident involved a driver travelling along the inner lane and striking a stationary object in his path. The accident resulted in a fatality and a lawsuit, alleging that the posted 80 kph speed limit was unsafe for the curve in question. Evaluate and comment on the road design (assuming that there is no problem with the vertical alignment). Intersection angle, D = 80 degrees. 6. For the compound curve in figure 6.8, if Δ1, Δ2, T2 and R 2 are known, find T1 and R 1. 7. A reverse curve is to be inserted between parallel tangents 50 m apart with AD = 350 m, and R 2 = 1.5R 1. Determine R 1, R 2 and Δ. 8. Derive equation 6.7 for the minimum radius of curvature. 9. Determine the length of tangent runout and length of runoff for a four-lane highway if the pavement is revolved about the centreline in order to achieve fully superlevated cross section. Maximum allowable longitudinal gradient is 1/200. Superlevation = 8% Total carriageway width = 13 m (6.5 m per direction) Normal crown = 1.5 % 2

10. Given: Design speed = 100 kph; emax = 6%; p = 0.5 m/sec . Sta. PI at 200 + 100.000 and Δ = 20 degrees a. Determine the parameter A for the symmetrical clothoid. b. Determine the stationing of TS, SC, CS and ST. c. Draw 1/R from station TS to ST. 11. A section of a two-lane, two-way highway (2 @ 3.5 m) is to be designed with a circular curve with transition (clothoid). The design requirements are the following: Design speed = 60 kph


Intersection angle = 40 degrees Superelevation rate = 7% Rate of change of acceleration: 0.5 m/sec2 Longitudinal gradient of superelevation runoff: 1/200 Determine the following: a. Radius of the circular curve b. Length of clothoid. 12. Show that tangents drawn from any two points on a vertical axis parabola always intersect midway between the points of tangency. 13. Show that

for crest vertical curves with S > L. 14. Show that

for sag vertical curves with S < L. 15. A new road is being proposed to intersect an existing highway at location P. Determine the length of vertical curve of the new road. G1 = -4%; G2 = 2%; Sta. P = 5 + 850.000; Elev. P = 200 m; Sta. BVC = 5 + 680.000; Elev BVC = 205 m


16. A 1.5 km straight tunnel is being constructed with work beginning at both ends. Unfortunately, due to an engineering mistake, it will not meet at the center. This would require a change in the vertical alignment (horizontal alignment is okay). The most efficient vertical design will be use the horizontal distance in the profile view. Design the connection using the highest common speed possible.

REFERENCES 

American Association of State Highway and Transportation Officials. 1984. A policy on geometric design of highways and streets. Washington D.C.



Hickerson, Thomas Felix. 1964. Route location and design. Fifth ed. McGraw-Hill Co.



Mannering, Fred L., and Walter P. Kilareski. 1990. Principles of highway engineering and traffic analysis. New York. John Wiley and Sons.



Ministry of Public Highways 1979. Highway Design, BCEOM (Third IBRD Highway Project-Technical Assistance Services), Manila.



Planning Service, Ministry of Public Works and Highways. 1982. The Philippine highway planning manual. Vol. 2. Manila.



Transport Training Center. 1983. Course notes on transportation and traffic technology. University of the Philippines.



Transportation Research Board. 2000. Highway capacity manual. National Research Council.



Wright, Paul H., and Radnor J. Paquette. 1987. Highway engineering. New York: John Wiley and Sons.

7: ROAD SAFETY AND TRAFFIC ACCID ENT ANALYSIS

7 ROAD SAFETY AND TRAFFIC ACCIDENT ANALYSIS 7.1 INTRODUCTION

One undesirable reality that comes with development is the increase in traffic accidents concomitant with increased motorization and infrastructure. Every year, worldwide, at least one million people are killed on the road, 70 percent of whom are from countries classified by the World Bank as low- or middle-income. This apparently worse scenario among developing countries, like the Philippines, may be explained in that priorities are geared toward infrastructure development, improving mobility, and addressing the need for a better public transportation system. Conscious efforts to ensure road safety then take a back seat.

7.2 ASSESSMENT OF ROAD SAFETY

The state of road safety of a country or a region is normally gauged by the frequency of accident occurrence. Key indicators are the number of accidents (fatal, injured, or property damage) and the rates of accidents. For comparison studies, the rates are normally used instead of the actual numbers.

7.2.1 Accident per Population One measure of accident rate is per 100,000 population. For instance, if a town, city, or region has N accident occurrences in one year and has a population P, then

 =   , 

(7.1)

Example 7.1 A town has a population of 350,000 in 2005. In the same year, the number of accidents was 620. Determine the accident rate.


Solution: Using equation 7.1, 620  = 350,000  100,000 = 177   100,000 

7.2.2 Accident per Registered Vehicles Another measure of accident rate is per 10,000 registered vehicles. Again, if there are N accidents in one year and the number of registered vehicles for the same year is V, then

 =   , 

(7.2)

Example 7.2 The town in example 7.1 has 122,400 registered vehicles in 2005. Determine the accident rate per registered vehicles.

Solution: From equation 7.2, 620  =   10,000 = 122,400 10,000 = 51   10,000 ℎ

Example 7.3 Given the number of accidents, population, and number of registered number of vehicles for each region in the Philippines, the accident rates are computed and shown in table 7.1. Most number accidents (72.44 percent) occurred in the National Capital Region (NCR) or Metro Manila. In terms of rate per population, Metro Manila still has the highest rate, followed on distant second by Region 10 (Northern Mindanao). However, in terms of rate per registered vehicle, Region 10 has the highest, followed by Metro Manila. It is recognized that the level or accuracy of reporting traffic accident varies from region to region.


Table 7.1 Distribution of accidents by region

7.2.3 Accident Definition The UN Organization (Geneva) defines traffic death as that which o ccurs within thirty days of the event, i.e., a road accident victim who died within thirty days of the incident is still considered a casually of the accident. The Philippines defines fatality as “death at the scene”. Serious injury and slight injury are defined based on the extent of injury sustained and the length of time required by the injured to recover. However, there is no exact definition of the seriousness of the injury. Property damage-only accidents involve vehicles colliding with publicity or privately owned structures, equipment, and facilities located by the road. It also includes collision of vehicles with other vehicles without causing physical injury to the driver, passenger, or any pedestrian.

7.2.4 Road Accident Reporting There are no specific steps in accident reporting in the country. In many cases, the accidents reported to hospitals are referred to medico-legal department of the hospital, with the local policeman from the accident site in attendance. In the absence of local police, the reporting of an accident from the hospital to the police headquarters and to the PNP is seldom done.


In Metro Manila, the Traffic Enforcement Unit is composed of three to five investigators working round the clock by shifts. Each accident case has a corresponding investigator from each reporting police station. It is a common practice for each investigator to be responsible for keeping the records of cases he or she has investigated, regardless of the type of accident. The TMG used to handle all cases of traffic accidents within Metro Manila, but when the Traffic Enforcement Group (TEG) was formed, both groups became involved in reporting and record keeping of traffic accidents. Although the TEG is supposed to be responsible for reporting traffic accidents while TMG takes care of anticarnapping and antihijacking campaigns, the functions of the two are still unclear as far as traffic ac cident reporting is concerned. The hospitals are usually the first ones to get involved within traffic accident victims. The police are then informed by a call from the hospital. At present, the practice of record keeping in hospitals varies considerably. Most of the hospitals do this manually. The Department of Health intends to promote an integrated hospital information system designed to computerized medical records. Several government projects on road safety are funded by international organizations. One relevant project is the DPWH Sixth Road Project (CO8 Road Infrastructure Safety Project). One of the outputs of this Asian Development Bank (ADB) funded project is the development of a handbook on accident cost estimation and updating. Another ADV-funded project implemented through the Metro Manila Development Authority and the Department of Environment and Natural Resources (DENR), the “Metro Manila Air Quality Improvement Project”, has a major component on road safety. It is interesting to note that both projects have developed traffic accident database and analysis system. The Traffic Accident Reporting and Analysis System or TARAS is housed at the DPWH. The TARAS is composed of computer software and associated procedures for recording and analyzing road accidents in the Philippines. On the other hand, the Metro Manila Accident Reporting and Analysis System or MMARAS is the computer software being used by the MMDA. The MMARAS is used for recording and analyzing road accidents in Metro Manila. Although the proponents of the two projects may assert that is is best to have two sep arate systems as they have different objectives to meet, in the end, what matters most is whether the two systems can give the overall picture of traffic safety in the Philippines. In the case of the MMARAS, only fatal and serious injury accidents are considered for reporting and analysis. This leaves the traffic investigation reports on minor injury accidents and property-damage-only accidents on the shelves


of the different police districts in Metro Manila. If integration of the two systems is not possible, at the very least coordination of tasks between the two agencies concerned is absolutely necessary.

7.2.5 Present Situation Most developed countries have been successful in reducing accident rates, but the rates remain unchecked in many developing countries. Relative to other countries, the Philippine accident rate of about 6.0 fatalities per 10,000 vehicles appears to show a better image of road safety condition. However, this figure may be misleading, considering the high incidence of severe accidents that have been reported in the newspapers. Are all these accidents accounted for? Do we have a good system of recording accidents? For what purposes are we compiling accident records? How are data kept? Are these data readily available to traffic engineers and planners responsible for analysis and for improving our transportation infrastructure? The lack of definite answers to these questions reflects how little priority is given to road safety. When the Philippine situation is compared with that of other ASEAN countries, again statistics may be deceiving and tend to make us complacent about our situation. In reality, there is much discrepancy between statistics and the actual situation.

7.2.6 Key Socioeconomic Indicators Three key socioeconomic indicators are used to assess a country’s road safety condition: A. Population B. Gross domestic product (GDP) C. Vehicle registration Population and number of registered vehicles have been discussed in section 7.2.1 and 7.2.2. Figure 7.1 shows the trends of these socioeconomic indicators of the country. As of 2003, Philippine population stood at about 80 million with a 2.2 percent annual growth rate. The GDP


Figure 7.1 Growth of population, GDP, and vehicle registration

was also increasing at about 5.5 percent annually while the total number of vehicles was fast increasing at the rate of 4.4 percent. Given the growth rates in all the factors, which increase the potential for road accidents, and based on the experience of most developing countries with similar trends, it is highly likely that casualties on the road should also increase over the years. However, this increase is not reflected in the reported road traffic accident statistics as collected and collated by the PNP. On the country, the trend in road accident deaths appears to be decreasing as shown in figure 7.2.

Figure 7.2 Number of fatalities on the road as reported by the PNP and the health sector


Everyone (including the PNP) recognizes the fact that because of the different agencies involved and the different jurisdictions, there is a serious problem in underreporting of traffic accidents by the police. An efficient road accident data system is simply not yet available in the Philippines. Moreover, hospital records are not reconciled with those of the police. Figure 7.2 shows that within the same period, the estimates of deaths due to vehicular accidents based on health statistics increased while police data indicated a decreasing trend. Up to 1998, the health sector used to compile statistics on deaths attributed to road traffic accidents (data are available for 1970, 1980, 1990, and 1998). In 2003, a UNICEF-funded study, entitled Philippine National Injury Survey, was conducted. This study revealed the seriousness of underreporting of traffic accidents in the country. Based on the study, about 9,000 fatalities could be attributed to road traffic accidents in 2003. As a cause of injury morbidity, road traffic accidents ranked first among other causes (fall, injured, struck by objects, burn, animal bites, etc.). In terms of mortality, the leading cause was infectious diseases (49 percent), followed by noncommunicable diseases (17 percent) and injuries (11 percent). However, as far as mortalities due to injuries are concerned, road traffic accident was the leading cause (20 percent), followed by gunshot (17 percent), stabbing (14 percent), etc. For the same year (2003), the police only reported about 900 fatalities. This problem of underreporting is expected to be more serious for the other types of accidents, namely, injuries and property-damage-only accidents. Based on the study of traffic accident victims using 2001 hospital data for very young people (below fifteen years old) were the most vulnerable age group (figure 7.3), representing 36 percent of the country’s total population. The number of fatalities for young people (fifteen to thirty-nine years old) was also high, with more than 70 percent of them being male. Figure 7.4 clearly shows that the most vulnerable road user group is the p edestrians. About 25 percent of the fatalities and 40 percent of the seriously injured pedestrians are less than fifteen years old.


Figure 7.3 Casualties by age group

Figure 7.4 Vulnerable user groups

Next to the pedestrian group, a growing concern is the motorcyclists. Over the last three years, the number of motorcycles grew by 40 percent per annum. Among the causes of traffic accidents, the police cited driver’s error, overspeeding, and overtaking as the major causes (table 7.2).


Table 7.2 Causes/nature of traffic accident (2003)

7.2.7 Accidents at Intersection As observed in other countries, intersections or junctions are also normally the points of conflict in the Philippine transportation system. Available data show that about one-third of accidents occurred at intersection (figure 7.5). However, local studies on the occurrence of accidents at intersections are very scarce, with hardly any reference on the subject.

Figure 7.5 Distribution of accidents by location (2000)


Table 7.3 shows the number of accidents involving fatalities in year 2000. Again the intersections accounted for the biggest share at 36 percent.

Table 7.3 Fatal accidents by location (2000)

7.2.8 Accident Rate for Intersections When analyzing traffic accidents at intersections, the total entering traffic volume usually in AADT is considered. Equation 7.3 is used to compute the accident rate per million entering vehicles (mev). The factor of 1,000,000 is applied for convenience to obtain values of Ai within two to three digits.

(7.3)

where

N – total number of accidents in time T T – time frame of analysis, year V – AADT or annual average daily traffic

Example 7.4 The T-intersection has 1,746 collision incidents over the last three years. The annual daily traffic is shown in the figure below.


Determine the accident rate of the intersection.

Solution:

7.2.9 Accidents Rates for Road Sections For segments oh highways 1-2 km in length, accident rates are computed based on total vehicle-kilometers of travel. Equation 7.4 is used to compute the accident rate per 100 million vehicle-kilometers (mvk). Again the factor of 100 million is applied for convenience. ,000,000  = 100365

where N – total number of accidents in time T T – time frame of analysis, year V – AADT or annual average daily traffic L – length of section in km

(7.4)


Example 7.5 A stretch of four-lane, two-way highway 5.0 km long has a traffic volume of 35,000 vehicles per day. If for the last three years, the total number of accidents recorded was 1,900, determine the accident rate per 100 mvk.

Solution: From equation 7.4

 = 100,000,0001,900  = 100,000,000 365 365335,0005 = 991.5   100  7.2.10 Accidents by Time of Day It is very alarming that most traffic accidents occurred during night time (see figure 7.6). There may be other contributing factors, but the major ones could be (a) inadequacy of street lightning, (b) lack of warning devices, and (c)0 complete disregard of traffic signals during late night or early morning. Driver factor again plays a big part, e.g., falling asleep, practice of using blinding head lights, drunkenness occurring more at night due to parties, reduced visibility due to smoke-belchers, and even occurrence of night blindness among malnourished drivers.

Figure 7.6 Distribution of accidents by time of day (year 2000)


7.3 IDENTIFYING HAZARDOUS LOCATIONS OR BLACKSPOTS

There are a number of methods in identifying blackspots or hazardous locations. Three methods will be discussed, two of which are based on statistics and the other based on a certain benchmark which is set considering budgetary constraints.

7.3.1 Classic Statistical Method The method assumes that the number of accidents at locations of interest follows a standard normal probability distribution. The method flags a location as hazardous if it satisfies the following inequality:

Table 7.4 provides a guide on the appropriate values of K for a given level of confidence.


Example 7.6 A highway section has an accident rate of 150 accidents per 100 mvk. If the mean accident rate for all sections is 55 per 100 mvk, and the standard deviation is 26 per 100 mvk, should the section under study be flagged as hazardous with 95 percent confidence?

Solution:

Applying equation 7.5,

The section under study has to be flagged as hazardous at 95 percent level of confidence.

7.3.2 Rate Quality Control Method This is a variation of the classic statistical method. Instead of a normal distribution, the method assumes that the number of accidents at a set of locations follows a Poisson distribution. Also, the method applies only to rates and not to frequencies. It compares the rate of a particular location to the mean rate at similar locations rather than at all locations. The method flags a location as hazardous if it satisfies the following inequality:


Example 7.7 A section of road has 55 accidents recorded in three years. For the same period, the estimated vehicle travel on the section was 23 mvk. Considering only those sections having the same characteristics as the section under study, the mean rate is 80 accidents per 100 mvk. Is the section hazardous with 95 percent level of confidence?

Solution:

�

The mean accident rate is

80 100 = .80 accidents per mvk.

For the road section under study,

 = 5523 = 2.39 accidents per mvk Using equation 7.6: 2.39 ? 0.80 + 1.645

0.5

 023.80 

+

1 2(23)

2.39 > 1.13

Therefore, with 95 percent level of confidence, the section is flagged as hazardous.

7.3.3 Setting Benchmark Method The third method requires arranging all accidents involving casualties from highest to lowest as shown in figure 7.7. When a certain benchmark is set, say five times of the average number of accidents, then the places of locations with more accidents than this benchmark will be considered as blackspots. Perhaps using this method is more suitable for the country, especially when budget allocation for improving hazardous locations is very limited.


7.4 RESPONDES TO SAFETY

7.4.1 The Inter-agency Road Safety Committee and the National road Safety Committee In response to the increasing concerns regarding road accidents nationwide and cognizant of the need to coordinate efforts of concerned government agencies and the private sector, the president of the Philippines issued Administrative Order 222 in May 1992, creating the Interagency Road Safety Committee (IRSC). The committee was chaired by the secretary of Public Works and Highways and composed of top officials of the Department of Transportation and Communication (DOTC), Department of Education, Culture and Sports (DECS), Department of National Defense (DND), Department of Health (DOH), Department of the Interior and Local Government (DILG), and the Safety Organization of the Philippines Inc. (SOPI) as members. Technical support and advice were provided to the IRSC by a technical working group (TWG), composed of representatives of key planning and operation units of members’ agencies. Since 1996, the DOTC has been given the responsibility to coordinate all road safety activities in the country and was assigned the chairmanship of the National Road Safety Committee (NRSC), which in effect replaced the IRSC.

7.4.2 Agencies and Institutions Involved in Road Safety The Department of Public Works and Highways is primarily concerned with the planning, design, and operation of roads and roadside facilities. In pursuing those functions, the DPWH requires data on road-related factors of an accident like location of occurrences, road condition of locations, and presence of road safety facilities. The on-going 6th ADB Road Project (Road Safety Component) being carried out by the DPWH covers major activities that are expected to boost road safety programs in the country. These are: •

interagency institutional arrangements including all aspects of the current IRSC to ensure improved interagency cooperation, taking into account the road safety provision of RA 8794.

•

organizational review, including the identification of deficiencies, existing legislations, and DPWH limitations;

•

•

road safety promotion in the overall planning process; publication of road safety manual;


•

development of a traffic accident recording and analysis system;

•

adoption of safety audits;

•

improvement of hazardous locations; and

•

development of key performance indicators and monitoring systems.

The Department of Transportation and Communications is the primary government agency dealing with road transport industry, particularly the planning and policy aspects. The DOTC h eads the National Road Safety Committee. NRSC is supposed to ensure the timely and responsive implementation of policies and programs on transportation safety. As far as road safety is concerned, a plan covering six aspects (6Es) has been developed; education, engineering, enforcement, enactment of laws, economics, and emergency services. The Philippine National Police-Traffic Management Group and the local police force have emerged as the main traffic law enforcement units of the government. The TMG, besides being involved in safety education programs, is responsible for the safekeeping of accident data. The Land Transportation Office is in charge of driver licensing, registration of motor vehicles, and the enforcement of transportation and traffic laws. Recently, when the drug test for drivers became mandatory, the LTO was tasked to accredit drug testing laboratories all over the country, in line with the agency’s target that no driver’s license shall be issued to drug addicts or drug dependents. The LTO carries out a driver education program with the assistance of Technical Skills Development Authority (TESDA) and in coordination with the Civil Service Commission to educate drivers on traffic rules and regulations, as well as to develop proper skills and behavior while driving. In the form of an outreach program, the LTO visits schools, bus companies, private and public organizations to conduct lectures to enhance road safety awareness. The on-going countrywide Motor Vehicle Inspection System/Smoke Emission Testing Project tests motor vehicles for emission and safety standards. Target results of the program a re improved air quality, reduced accidents, reduced fuel consumption, and reduced air-quality-related health problems. The Land Transportation Franchising and Regulatory Board is a quasijudicial agency mandated to rationalize, regulate and supervise motorized land-based public transport service. The Metro Manila Development Authority has jurisdiction over the delivery of basic u rban services in Metro Manila, including land use planning and zoning, traffic management, public safety, urban development and renewal, and sanitation and waste management. It performs


planning, monitoring and coordinating functions for services that have metrowide impact and transcend political boundaries of the sixteen cities and one municipality of the National Capital Region or Metro Manila. Specifically it is responsible for coordinating and regulating the implementation of all programs and projects concerning traffic management. It is tasked to administer a single ticketing system and fix, impose, and collect fines, and penalties for all kinds of violations of traffic rules and regulations through its Traffic Operation Center. The Department of Health, the principal health agency in the Philippines, is responsible for ensuring every Filipino’s access to basic public health services through the provision of quality health care and regulation of providers of health goods and services. Given the mandate, the DOH is both a stakeholder in the health sector and a policy and regulatory body for health. As a major player, the DOH is a technical resource, a catalyser for health policy, and a political sponsor and advocate for health issues on behalf of the health sector. The Department of Education (DepEd) is the primary government agency tasked to provide the school—age population with basic education. It has been long proposed that traffic education be included in the high school curriculum, but so far, a bill has yet to be discussed in the legislature. The University of the Philippines National Center for Transportation Studies (UP NCTS) plays a major role in human resource development in the field of transportation. The center conducts training and research in the fields of transportation planning, traffic engineering, and traffic management. A number of subjects related to road safety – road safety programs, accident investigation, reporting, and analysis – are offered as part of the curriculum of the regular training programs for the participants of traffic engineering course and traffic management for traffic law enforcers course. The Safety Organization of the Philippines Inc. (SOPI) is a private organization operated by donations from private companies as well as from government agencies. The activities of SOPI cover not only road safety but also the prevention of nay types of accidents. The month of May is set by SOPI as the “Road Safety Month” during which it conducts road safety campaigns in cooperation with private companies and government agencies. Aside from annual national meeting on road safety, SOPI issues booklets and other materials for road safety education. The Automobile Association Philippines (AAP), formerly the Philippine Motor Association, is a private organization that has dedicated itself to the promotion of motoring and to the service of the Philippine motorists for more than half a century. This organization also serves


the needs of Philippine motorists worldwide through its affiliation with the two most distinguished motoring federations in the world: the Alliance Internationale de Tourisme and the Federation Internationale de l’Automobile. Members of the association can avail themselves of a number of privileges, such as twenty-four-hour roadside free-towing services within Metro Manila, discounted driving lessons, free motor vehicle registration service, twenty-four-hour ambulance service at minimal cost, international driving permit, and accident investigation assistance. In the smallest administrative unit, which is called the baranga y, volunteers serve as traffic aides. They assist the traffic police in controlling traffic at bottlenecks and in case of accident occurrence.

7.5 INITIATIVES ON ROAD SFETY

Among the most recent initiatives that the government has introduced are the following:

7.5.1 Imposing a Motor Vehicle User’s Fee on Owners of All Types of Motor Vehicles (RA 8794, 2000)

Section 7 of RA 8794 provides, among others, that 7.5 percent of all monies collected under this Act shall be allotted to and placed in the special road safety fund under the DPWH. Also under the Act, a portion of the special funs shall be appointed to provincial and city governments in accordance with the vehicle population and side of the road network under their respective jurisdictions, and shall be used exclusively for maintenance of local roads, traffic management, and road safety devices.

7.5.2 Motor Vehicle Inspection System by the LTO Inspection of motor vehicle is a prerequisite to vehicle registration, with the objective of ensuring that the vehicle is in good condition. Structural and safety components of the vehicle ae officially examined.

7.5.3 Seat Belt Law (RA 8750) The seat Belt Law, passed in year 2000, requires installation of and buckling up of seatbelts on front seats only of private vehicles. No special requirements are stipulated for children. For


public utility jeepneys, only the driver and the passengers seated in seats facing forward are required to wear seatbelts. In the case of public utility buses, only the driver and the passenger seated immediately behind the driver, and the passengers seated immediately behind the door of the bus are required to wear seatbelts.

7.5.4 Banning the Use of Cellular Phones and Handset Radios while Operating or Driving a Motor Vehicle (RA 7924)

The se of cellular phones while driving has been banned within Metro Manila since March 1997 because of its potential hazards to motorists. Though still small in number, accidents that were primarily attributed to using cellular phone while driving have occurred.

7.5.5 Other Initiatives As mentioned earlier, the UNICEF Philippines conducted a study on the reduction of incidence of childhood death and disability resulting from preventable injuries on 2003. This study was similar to the first project on Child Injury Prevention supported by the UNICEF in Vietnam. The results of the study have confirmed the seriousness of the country’s problem regarding road safety and unreliability of data as provided by the police.

7.6 ROAD SAFETY ISSUES

There is a need to stress the urgency of improving safety on our roads. The following should be given priority in addressing the issue of safety:

7.6.1 Legislative There seems to be a general consensus that majority of road accidents are attributed to driver’s error. The government must not delay implementing stronger driver licensing control and driver improvement programs, the first step in weeding out undesirables on the road. The licensing system in the Philippine is to lax that one does not have to learn how to drive before getting a driver’s license. Driver licensing requirements should be tied in with driver education.


There is an urgent need to reconvene the National Road Safety Committee, which has not met for a long time. A more powerful national safety committee is necessary to formulate action plans or develop agenda toward reduction of traffic accidents in the country. Campaigns prohibiting street children, vendors and the like on the carriageway and sidewalk cleaning of vendors must be continued. Banning of dilapidated (road unworthy) vehicles on the road must be strictly enforced. Overloading of passengers must be strictly prohibited. The road right of way must be assigned for carriageway of the road users, paths for pedestrians, for installation of appropriate traffic control devices, etc. No commercial advertisements should be mounted or installed within the road’s right of way as they compete for driver’s attention.

7.6.2 Institutional Availability of reliable data on accidents is key to understanding how the transportation system works. However, without a systematic method of accident data collection, processing, and analysis, the overall picture of road safety in the Philippines remains obscure. The seemingly rosy picture depicted by statistics must not make us complacent as these cannot simply cover up for the failure of our transportation system comprising the road, the driver, and the vehicle. There must be a wholehearted commitment to improve traffic accident investigation, reporting, and analysis. While computer databases, on traffic accidents have been developed at the DPWH and the MMDA, integration of the two is necessary to establish an integrated accident database incorporating police and hospital reports. Figure 7.8 shows the structure of the proposed integrated traffic accident data management system. This is possible only if there is a very strong linkage between the police and the hospitals. This may be achieved by undertaking a memorandum of agreement between the DIG and the DOH. Sustainability of the on-going efforts in maintaining the accident databases has to be strongly considered.


7.6.3 Technical As to the road environment, whatever changes in control or geometric improvements applied to intersections or roadways bring about significant change in accident occurrence and accident rates. Caution is therefore advised when conducting test runs or experiments without prior careful analysis. A trial-and-error method of solving traffic problem must be avoided. Since many accidents occur during night time, efforts must be exerted to improve visibility at night. Placement of appropriate traffic control devices (warning devices, delineators, reflectors, etc.) at hazardous locations can help minimized accidents. Figure 7.9 shows a section of the NLEX installed with traffic control devices.


Improved uniform warning traffic signs and marking devices on all roads must be applied; rules must be written in a concise, readable way and placed in prominent spots. Along highways, guardrails and median barriers keep vehicle from straying (in most cases unintentionally) into dangerous or off-limit areas. Figure 7.10 shows an example of W-beam guardrail and the New Jersey median barrier. Guardrails must be used to prevent vehicles from veering off a road into oncoming traffic, crashing against solid objects (like a bridge pillar), or falling into a ravine. Guardrails and medians also keep the vehicle upright while it is deflected along the barrier.


Some of the traffic calming measures may be adopted to improve safety for pedestrians and bicyclists as well as improve the environment for residents. Calming measures are now very common in Europe and in North America. According to the Institute of Transportation Engineers’ definition, traffic calming is a set of street designs and traffic rules that slow and reduce traffic while encouraging walkers and cyclists to share the street. Behind traffic calming is the belief that streets are valuable public spaces that should be shared equally by all users. Traffic calming devices are simple, inexpensive, self-enforcing, and easily modified to accommodate emergency vehicles, garbage trucks, and buses. Traffic calming has been widely used to reduce traffic accidents, increase the safety and convenience for pedestrians and other non-motorists, give more space for children to play, eliminate noise and pollution, improve scenery, provide neighbourhood revitalization and stability, and reduce crime. There have been a number of calming measures implemented successfully, some of which are as follows: a. Raising the surface of the street in certain spots – for example by installing speed humps (figure 7.11)


b. Adding fixtures around which motorists must drive – such as landscaped islands or small roundabout in the middle of intersections (figure 7.12)

c. Narrowing the street, to give drivers the feeling that they’re in a crowded place, which helps make them slow down d. Totally or partially closing a street – for example, by blocking half the entrance to a size street to so drivers cannot turn in, but can still come out

Research on the area of traffic safety has not been given a full attention here in the country. But several questions need to be answered in order to develop a better traffic safety program: Where are the high accident locations? How many were killed and injured last year? Where? When? How? Some of the more urgent topics for research are as follows: a. Real causes of motor vehicle accidents, as differentiated from circumstantial factors b. Driver behavior and accidents (speeding, inattention, ignoring traffic control devices, drunk driving, driving on drugs, failure to “buckle up”, etc.) c. Relation of specific road and vehicle design elements to highway safety d. Monotony and fatigue problems in expressway driving or in a long-distance driving. e. Developing improved means of communication from the highway to the individual user and between drivers. f. Estimation of cost of traffic accidents.


7.6.4 Education and Campaigns There must be a continuing program to increase the level of awareness on road safety. The program must include expanded and proper use of all media. Safer pedestrian habits both through education and control measures must be given importance. Figure 7.13 shows the teaching modules intended for Grade 6 and fourth year high school levels.

7.6.5 Sociocultural It is a familiar saying that anyone who can drive in the Philippines can drive anywhere in the world. It means experiencing driving on Philippine roads is like going through the most challenging driving situations. The prevalent mentality of “pwede na ‘yan” a mindset of mediocrity and getting one’s way out of trouble, makes rules and regulations practically useless. It is a s if chaos is a better or more acceptable stable to be than having some order to things. Commuters wish to get off at any point at their whim and fancy, and drivers of public utility vehicles give in.


Drivers themselves pick up passengers at any point even if it means blocking a whole trail of vehicles behind them. They do not observe the right of way but have their own habit of “ngusuan” – that of sticking out their vehicle first so as to get ahead first. The culture of corruption penetrates all sectors of society, not to exclude traffic matters. Due to bribes or under-the-table transactions, there are licensed drivers who are underage, illiterate, drug add icts, don’t understand road rules or traffic signs, drive even when drunk, have bad tempers, and use their guns at the slightest road quarrel or irritation.

7.7 COST OF TRAFFIC ACCIDENTS

The present world scenario depicts that traffic accidents claim approximately two human lives every minute. Besides causing prime loss in terms of human lives, these occurrences also bring about tremendous amount of wastage in terms of finances, property, time, resources, and services. Medical efforts alone geared toward the treatment and needed rehabilitation of accident victims are obviously huge and tedious. Investigation and litigation processes involved can also be very taxing not only financially but also emotionally for the bereaved and grieving family. A great amount of labor resources is likewise lost as manpower is reduced due to absence form work for treatment or for processing insurance claims, absence due to injuries with disabilities, and actual loss of human assets due to deaths. In the Philippine setting, just a single traffic accident can be peculiarly costly as it has a potential to cause heavy traffic jams due to too much delay in the investigation and rescue processes. This in turn causes additional losses for all the other people affected. While the problem of road safety is improving in developed countries, the situation seems to be getting worse in developing ones where priority is more focused on providing transportation infrastructure geared toward improving mobility of people (Sigua 2000). The very high growth rate of vehicles in developing countries has compounded the problem of road safety. In the past ten years, the volume of vehicles in the Philippines has more than doubles (1.88 million in 1992 and 4.19 million in 2002). Once merely a status symbol, owning a car has become a nec essity due to inadequacy of public transportation services and has contributed to the deterioration of the environment through pollution. The lack of driver education and weak enforcement exacerbate the


situation. Overspeeding and complete disregard for and lax implementation of traffic rules and regulations have contributed to the rise of casualties on the road. Life is considered most sacred, and there seems s eems to be a strong disagreement whether to put a monetary value on it or not. Some people are uncomfortable or emotionally very reluctant to assess traffic accidents involving human lives in terms of money. For while properties and financed may be restored, human lives lost cannot. Putting a monetary value to human life or to a fatal accident may be a topic for heated debate but the same lack of cost estimates leaves many, including the decision makers, still groping in the dark. But if it would create awareness of the worsening road safety situation in our country alone, an estimation of the losses attributed to traffic accidents is very well justified. Like the growing concern for the environment, it is high time that the government takes action in promoting safety on the road. If realistic estimates of the cost of losses can be made, there is no reason why the government cannot take action in reducing it. The estimate must truly reflect the actual worsening condition of our roads as far as safety is concerned. While it is recognized that data gaps exist, reasonable assumptions must be made as an initial attempt. Improvement of the estimate can be done in the future as data become readily available and collection efforts improve.

7.7.1 Uses of Accident Cost Estimates The reason for estimating accident costs may seem obvious but it is seldom expressed explicitly. Costs are sometimes used for general statements such as “Accidents in (country) are worth more than (so many) (million dollars) per year,” or accidents are (so many percent of a country’s GDP). For such purposes, ballpark figures are sufficient as long as they are of the right magnitude. (Andreassen 1988). Costs are also required for assessing the value of improving a highway, installing traffic signals, enforcing specific traffic laws, putting reflective plates n trucks, various safety countermeasures, etc. When these are to be considered, a very specific cost is required to determine the benefit. The promotion of traffic safety contributes to improvements of the welfare of society in two ways (OECD Report, 1981): a. BY voiding accidents and accident consequences the losses of resources caused by accidents are avoided as well.


b. By avoiding accidents and their social costs, resources can be saved, which otherwise would be devoted to the relief of accident consequences.

The first point includes the avoidance of production losses due to the incapacity of accident victims, damage to capital goods, and traffic congestion resulting from accidents. The second point includes the avoidance of the following costs: medical treatment of persons involved in accidents, repair of property damage, police investigation, legal and court procedures, and insurance administration. The resources saved can be used elsewhere to increase welfare.

7.7.2 Approaches to Estimating Cost of Accidents A number of methodologies to estimate the cost of accidents have been introduced in the past, including the following: a. Gross output/ human capital method b. Life insurance method c. Court award method d. Implicit public sector valuation method e. Net Output Method f. Value of risk change or willingness-to-pay method

These methods are documented by Alfaro, Chapuis, and Fabre (1994); Jacobs (1995); and Babtie Ross Silcokc and TRL (2003). The life insurance method measures the valuation of risk associated with road usage and is determined by the premiums that he driver population is willing to pay. On the other hand, the curt award method is based on the actual compensation settlements awarded, which may be influenced by the degree of negligence found. In the implicit implicit public sector valuation method, a set set of implicit values is used to value human lives. However, most of these estimation methods have been generally discredited (Babtie Ross Silcock and TRL 2003). To date, the two commonly accepted methods to estimate the economic cost of accidents are as follows:


a. Gross output or human capital method. This approach focuses on the economic consequences of a road accident, and usually also includes a notional sum that reflects the pain, grief, and suffering incurred by the persons involved and their family. It is based on the idea that the value to society of avoiding a death or injury is related to the potentially lost economic output and resources. b. Willingness-to-pay method. This is based on the amount that a person is willing to pay to avid an accident. This is a very subjective measure that reflects individual preferences, values, and perceptions of risk. It is extremely difficult to reliably estimate and will vary significantly from person to person and from place to place.

The willingness-to-pay method has become the preferred costing method in many developed countries as it has been recognized as the best way to measure the costing of accidents for the purpose of benefit-cost analysis. Recognizing the difficulty of implementing this method in developing countries due to its data requirements (the method relies on the completion of a complex questionnaire), the ADB publication Road Safety Guidelines for the Asian and Pacific Region recommends the gross output method. The guideline considers is as the appropriate method

to be used in developing countries because it relates more closely to direct economic impacts and the practical measurable consequences of road accidents. That is the approach used in this cost estimation, and the detailed methodology for dealing with data gaps, underreporting, etc. is in line with the guidance document provided to the author by the ADB

7.7.3 Determination of Cost Components Consistent with the gross output method and the ADB guidelines, the accident cost components can be grouped into five major cost categories shown in table 7.5:


Lost output Lost output is generally considered as the largest resource cost incurred due to a traffic accident. It is an expression of the loss to society of the productive manpower, be it permanent or temporary. Its value varies widely, ranging from a one day lost time for minor injury incident, to long years of foregone work for those killed or permanently disabled.

Pain, grief and suffering Strictly speaking, mental suffering, pain and other emotional factors cannot be assessed. They defy evaluation in terms of money, and must therefore be taken as a true intangibles. However, in practice some countries add an assumed lump sum or proportional amount to measured accident costs to allow for emotional losses.


Medical treatment and hospital costs The treatment and rehabilitation of traffic accident victims require the use of medical resources, i.e., work input of the personnel (ambulance men, doctors, nurses, etc.) and provision of rescue equipment, hospital beds, instruments, and other medical aids, such as drugs. If injuries caused by traffic accidents could be avoided, these resources could be made available for other purposes, such as treatment of the sick, or their basic components could be transferred to other uses. The following components can be distinguished: a. On-the-spot medical treatment b. Transport and treatment on the way c. Treatment at the hospital d. Rehab at the hospital e. Outpatient follow-up treatment f. General treatment

Although considerable parts of the medical expenses are paid only to those who provide such medical services, they may still be regarded as losses to the economy because such services would have been otherwise provided elsewhere if the traffic accidents had not occurred. The same applies to the repair charges of damaged vehicles and legal fees.

Property damage Property damage necessitates or replacement costs of vehicles, goods, and road accessories. In addition, property damage can result in further welfare losses when capital goods (e.g., trucks, cars for commercial use, equipment, etc.) are damaged or destroyed and their productive services are lost. When private passenger cars are damaged, additional welfare losses may result from the loss of use. For the determination of property-damage-only involvement costs, insurance records can be used and the compensation taken as indicator of social losses. Account has to be taken of the fact that insurance companies generally pay compensation for liability cases only, and are liable for accidents brought on by one’s own fault only to the extent of a contracted limit. In addition, it should be noted that there may be considerable difference between the cases recorded by the insurance companies and the police records.


With respect to property losses, evaluation is relatively eas y because the market prices and repair charges for the property lost or damaged can be regarded as a good expression of the objective values.

Administrative costs The police are called out to the sites of traffic accidents to control traffic and investigate and record the accidents. Total work hours required for handling traffic accidents have to be considered. A patrol car is dispatched to each traffic accident site to control traffic and deal with the accident. Since the patrol car is also used for other purposes, half of its total expenses will be taken up in connection with traffic accidents. In addition, the police headquarters headq uarters uses cameras for photographing accident sites. Some of the other components of administrative costs are judicial costs and insurance administrative costs. The functions of the court dealing with traffic accidents include (a) civil suits for damages, (b) civil mediation, (c) criminal suits for negligence, and (d) summary criminal procedures. Most of the damage caused by traffic accidents is covered by insurance, and the operating expenses required to support this system also constitute part of the costs and expenses incidental to traffic accidents. Figure 7.14 provides a summary of the different cost components that may be involved in each accident, depending on the type of severity:


Based on the diagram, a fatal accident would incur loss of productive life of the victim: pain, grief, and suffering of loved ones left; medical expense when the victim was brought to the hospital before dying; a number of miscellaneous expenses that would constitute administrative costs; and cost of a totally wrecked vehicle or cost of repair of a damaged vehicle. Similar cost components may be incurred when a victim becomes permanently disabled due to a serious injury accident. A minor injury accident would still incur some medical costs and require some paper work, and, possibly, minor repair of a slightly damaged vehicle.

Other assumptions A range of assumptions underlie the recommended methodology. The major additional assumption is that all accident are costed out as though all steps were taken to restore people, vehicles, and property as closely as possible to their condition prior to the accident. It means that: •

injured persons receive full medical treatment, are treated in a hospital if seriously injured, and recuperate for the recommended period;

•

injured persons are considered to be employed (or potentially employable);

•

vehicles are repaired according to manufacturer’s specifications; and

•

an accident report is made, all the proper paperwork is completed, and insurance claims are filed and recorded accurately.

Some indirect costs of accidents Aside from the major cost components previously discussed, there are other costs that may be attributed to traffic accidents. One is the cost of transportation services for the injured from the accident spot to the hospital. In a number of cases, the law-abiding “offender” is the one that brings the victim to the hospital. In some cases, a concerned citizen may offer his or her vehicle to bring the victim to the hospital. It is seldom that a hospital ambulance would be called to the rescue of the victim, although at present, ambulance services provided by some rescue teams may be summoned to the accident site when notified by a phone call.


Losses caused by traffic congestion Traffic accidents often caused bottlenecks. A few minutes of congestion can easily create gridlocks at intersections and several kilometres of vehicle queues in urban areas. The people affected by such bottlenecks incur loss of time and fuel, and suffer both mental and physical stress.

7.7.4 Estimation of Cost Components Following the ADB guidelines, the gross output method requires a procedure that is relatively easy to follow. What remains is the problem of collecting pertinent data that will be used as inputs in the step-by-step procedure. While collection of such data does not pose a major problem in developed countries, it becomes a major task in developing countries like the Philippines. It must be stressed once again that traffic accident data are very valuable: data collection, therefore, requires conscientious effort on the part of the agencies concerned.


Underlying assumptions The gross output method requires input to a number of variables incorporated in each cost component. Some of these variables require estimation from available secondary data. However, some variables cannot estimation unless comprehensive primary data collection is conducted. In this case, assumptions based on the experience of other countries are made. Nevertheless, estimation of the cost of accidents has to be updated on a regular basis. At this point, it is very important to determine those on variables that have deficiency in data availability. Determination of these variables can then be incorporated in the research agenda on mad safety. The National Center for Transportation Studies of the University of the Philippines has actually initiated the formulation of research agenda as far as traffic safety is concerned. One notable research on traffic analysis focusing on hospital records (Vibal 2003) proved to be very valuable in determining the extent of severity of human damage attributed to road crashes.

Average age of seriously injured Based on Vibal’s study, “Traffic Accident Analysis through Hospital Records” (2003), which examined 617 cases of serious injuries in road accidents (including forty-four fatalities), the average age of seriously injured persons, was twenty-eight years. The most seriously injured persons were in the age range of thirteen to thirty-nine years. Average age of fatalities This has been assumed to be the same as the average age of persons seriously injured.

Damage to property Damage to property can be obtained from insurance companies based on property damage claims for motor vehicle accidents. Property damage costs can var y considerably depending on the degree of wreckage sustained. It may therefore be necessary to obtain estimates based on accidents stratified according to severity. As previously mentioned, the repair costs are calculated as if all vehicles are repaired according to manufacturer's specifications, since represents the resource cost to the community of vehicle damage. Information on average claims was supplied by the Insurance Sure the Philippines (ISAR) on a confidential basis. The average claim was converted to 2003 figures, and allowance was then added for total wrecks, owners cost input and towing. In general, vehicles involved in


fatal serious injury accidents will be damaged more severely than ears accidents in which nobody is injured. No data are currently available the relative cost of damage by injury severity. International experience indicates that the relative repair cost of accident types compared average cost is as follows: Fatal accident 1.55 times average cost Serious injury 1.40 times average cost Minor Injury 1.25 times average cost Damage-only 0.85 times average cost These translate to P46,500 per vehicle for a fatal accident P42,000 per vehicle for a serious injury accident P37,500 per vehicle for minor injury accident P25,500 per vehicle for a damage-only accident

Administrative costs The cost is composed of several components as there are many agencies administering services related to the accident—traffic police, emergenc y response services, insurance, and legal services. It is therefore, very difficult to compute this cost. This is compounded by the problems of underreporting and the lack or complexity of administrative linkages. The ADB guideline is followed in estimating the administrative cost. The ADB recommends that the administrative cost be taken as a percentage of total resource costs (sum of lost output, medical and property damage cost). Similar to property damage, the administrative costs associated with an accident are likely to depend on its severity. In a more serious accident, vehicles may remain on the road longer, and more policemen may be assigned to direct traffic. There is also the longer and more complicated process of investigation, claims and follow-ups, and possibly legal proceeding. The ADB recommends the following: Fatal accident 0.2% of total fatal accident resource cost Serious injury 4% of total serious injury resource cost Minor injury 14% of total minor injury resource cost Damage-only 10% of total damage-only resource cost


Medical costs Medical costs vary widely depending on the severity of the injury. Serious injury could mean long hospitalization and rehabilitation. a. Serious injury i. Stay in the hospital

In a recent study of traffic accidents using hospital records (Vibal 2003), victims' hospital stay depending on the severity of injury is as follows: six to eight days and seventeen days for typical and more severe pedestrian accidents, respectively; five to six days for typical motorcycle accident and nineteen days for more severe motorcycle cases. For the purpose of this study, an average of eight days of stay will be used for estimating cost. During this eight-day period of stay in the hospital, it is necessary to take into consideration the amount incurred due to hospital care. Based on the rates in a tertiary hospital with daily visits by a general practitioner, two visits by a specialist, drugs and medicine, and one episode of minor surgery plus an allowance for the cost of ambulance transfer to the hospital, total cost of hospital care is estimated at P4,000 per day. This amount Paid in full by the patient without subsidy from the government.

ii. Recuperation period

While recuperating at home, the injured may still be undergoing medication. During this period, the person is also off work. As there are no data with regard to recuperation period, information from experience of other countries may be used. In the case of Australia, a study has shown that, on the average, a person recuperating from hospital treatment will have an additional 2 days off work for every day of stay in the hospital. This has been confirmed by medical practitioners in Manila.

b. Minor injury In the case of minor injuries, two visits to a doctor can be reasonably assumed; the first visit is for initial assessment of the injury while the second is for follow-up. Costs incurred during each visit may be as follows: P250 for consulting services and another P250 fur medication, bandages, etc. Say, P500 per consultation.


c. Permanent disability When a seriously injured person becomes permanently disabled, the cost will include medical expenses, special equipment (wheelchair or special bed), and employing a nurse. In case a family member acts as caregiver, the cost also includes lost income due to his or her absence from work. In the absence of data on long-term care, about P100 per day is assumed to cover the costs of long-term care for the permanently disabled. Based on limited records so far inputted to TARAS of the DPV/H, the following information was obtained. (It is recognized that when more data are collected, better estimates can be obtained.) Average number of vehicles involved in each accident type: 1.4 vehicles per fatal accident 1.5 vehicles per serious injury accident 1.5 vehicles per minor injury accident 1.8 vehicles per property damage accident

Average number of injuries in a fatal accident: 1.1 fatalities 0.4 serious injuries

Average number of injuries in a serious injury accident: 1.5 serious injuries

Average number of injuries in a minor injury accident: 1.1 minor injuries

7.8 ESTIMATION OF AVERAGE COST OF ACCIDENTS

In this section, computation of average cost for each type of accidents will be shown. The estimates are based on values of the different variables explained in the previous chapter (Cost Components) and follow the calculation procedure given on table 7.6.


7.8.1 Estimation of Cost of a Single Fatal Accident The estimation of the cost of a fatal accident requires the calculation of the five cost components: lost output; pain, grief, and suffering; medical cost administrative costs; and cost of repair of the damaged vehicle (see table 7.7). The estimated average cost of a fatal accident is approximately P23 million.

7.8.2 Estimation of Cost of a Single Serious Injury Accident The same cost items are considered in estimating the average cost N3/4,000"us injury accident (table 7.8). The estimated average cost is


7.8.3 Estimation of Cost of a Single Minor Injury Accident The estimation of the average cost of a minor injury accident requires the calculation of three cost items: medical cost, repair of vehicle cost, and administrative costs. A single minor injury accident would amount to approximately P70,000 ( table 7.9).

7.8.4 Estimation of Cost of a Single Property-Damage-Only Accident Aside from the cost of repair of a damaged vehicle, administrative cost is also incurred when a damage-only accident occurs. A damage-only accident would cost about P55,000 (table 7.10). (This excludes cost only may be incurred due to repair or replacement of damaged road signs and other street fixtures.)


7.8.5 Summary of Average Cost of Each Type of Accident Table 7.11 shows the summary of average cost of accident by type. Using the propertydamage-only (PDO) cost as point of reference, the average cost for fatal injury is about 40x higher; for serious injury, 6x; and for minor injury, 1.25x.

7.9 ESTIMATION OF NATIONAL COST

Once the average cost of each type of accident is obtained, the total cost of accidents may be estimated by multiplying the total number of accidents of each type by the average cost. Again, the types the analysis are as follows: a. Fatal accident b. Serious injury accident c. Minor injury accident d. Property-damage-only accident

7.9.1 Data Availability and Quality In the Philippines, researchers rely mostly on accident data provided by the police. More specifically, the Traffic Management Group which is responsible for accident data keeping for the


whole country. It is generally accepted that there is a serious problem in the reporting of accidents because of the following reasons: a. Although the Philippines recognizes the UN Organization's definition of traffic death— one that occurs within thirty days of the event—our count is still based on "death at scene." Even though most countries still use different definitions, their accident statistics are adjusted by applying correction factors to conform to the standard definition. Our current system of accident data keeping makes statistical adjustment almost impossible to do. b. A major cause of the underestimating of traffic accident statistics in the Philippines is the lack of an effective means of updating fatality and injury data. At present, the country has yet to develop a system of transferring records from hospitals to the TMG c. Recording and updating are prone to errors as done manually. There are also cases of records getting lost or of misplaced.

Even the PNP itself acknowledges that there is a serious problem of underreporting of traffic accidents. Aside from the absence of an efficient road accident data system, there is a great discrepancy between hospital and police records. Figure 7.15 shows the official statistics from the health sector. Deaths attributed to traffic accidents in 1970, 1980, 1990, and 1998 are available from the Philippine Health Statistics. In the 2003, Philippine National Injury Survey funded by the UNICEF, approximately 9,000 fatalities were attributed to road traffic accidents, a tremendous


increase from the 1998 of 3,800. For the year 2002, the police, in contrast, reported only 801 fatalities, clearly show a very serious problem of underreporting. The situation of underreporting for injury cases is far worse than that for fatal cases. A number of previous studies have highlighted the relationship between the number of crash deaths and injuries. Barrs et. al. (1998) quoted a generic ratio of 10:25 injuries to deaths (with half requiring hospitalization), but the only developing country example Included was from an urban hospital study in Ethiopia, which reported sixteen injuries for every death (Dessie and Lawson 1991). A three-month study conducted by Malaysia's Public Health Department (Rahman 2002) reported 19,271 casualties receiving treatment at hospitals. Of these, 1.3 Percent were fatal and 79 percent received outpatient treatment. Thus for every road death, there were fifteen hospitalized and another sixty-one slightly injured. Underreporting was believed to be much greater for injuries than deaths (Jacobs, Aeron-Thomas, and Astrop 2000). To estimate global road casualties, the study adopted a ratio of 100 injuries to a fatality for high-income countries, while a conservative road death to injury ratio of 20:30 was used for low-income countries. In the first Safe Community Conference on Cost Calculation and Cost-Effectiveness in Injury Prevention and Safety Promotion, a ratio of 70 slight injuries and 15 serious injuries to every death was suggested to apply to most countries (Barrs et al. 1998). In the case of the Philippines, three major hospitals having the highest number of in patients with traffic accident-related cases were studied (Vibal 2003). The study primarily focused on fatal and serious injury cases only. Out of the 1,242 cases (with 94 unspecified cases), 67 (5.4 percent) were fatal cases and 1,081 (87 percent) were serious injury. cases. This gives a serious injury to death ratio of 16:1, which is consistent with the results of the previous studies mentioned above. In the absence of data on slight injury cases, a ratio of 70:1 will be adopted. It is far more complicated to estimate the number of property damage-only accidents because such cases are even more underreported. In the absence of data on this, the estimation of the number of this type of accident will be based on the ADB guideline of five damage-only accidents for each injury accident. Again, as data collection efforts improve, a local value for the Philippines may be estimated more accurately. In preparation for the estimation of national cost of accidents, it is necessary to determine the numbers of accidents by type since the individual costs are estimated using that same unit.


Based on the TMG’s statistics of recorded traffic accidents for the year 2002, the breakdown for each type is shown in table 7.12.

Applying the corrections attributed to underreporting and the other assumptions adopted in the previous section, the number of accidents is adjusted (table 7.13).

7.9.2. Calculation of National Costs Applying the average cost of each type of accidents, the national cost of accidents is calculated as shown in table 7.14


Without any corrections to the accident statistics collected by the responsible agency, the cost of traffic accidents is about P2.5 billion or US$ 45 million each year. However, this is a gross underestimation as it has been shown that there is too much underreporting of accidents. The estimate cost based on the health sector data amounting to P105 billion (or US$ 1.9 billion) may still be on the low end because many cost components were not accounted for during the application of the gross output method. But this cost is already about 2.6 percent of the Ph ilippines’ GDP. A better estimate of the cost is expected when more accurate statistics are made available due to improved data collection system.

PROBLEMS

1. In planning for highway improvements in a particular region, the traffic accidents have to be analyzed to give priority to those hazardous or accident-prone locations. The table below shows the twenty sections considered for analysis. Sections marked with an asterisk (*) have almost similar characteristics in terms of physical and traffic conditions. Among these marked sections, which would you consider hazardous at 95 percent level of confidence? Use a. classic statistic method b. rate quality control method


2. The five-leg roundabout shown below was the scene of 850 accidents in 2004. The annual average daily traffic is shown in the corresponding route OD table. Determine the accident rate of the roundabout.


3. The figure below shows the road network inside a town proper. According to accident statistics over the last three years, the ten intersections having the highest number of accidents are shown in the corresponding table. The total entering traffic for each intersection is also shown. Identify the intersections that may be considered hazardous, using 95 percent level of confidence.

4. The table below shows the average cost of traffic accident by type:

Based on the experience of a similar country: Ratio of seriously injured victims to fatal victims: 16:1 Ratio of minor injured victims to fatal victims: 60:1 Number of vehicle-damage-only accidents: 5 times the number of serious injury accidents


Based on accident statistics: a. 1 fatal accident → 1.1 fatalities + 1.5 seriously injured victim s + 1.0 minor injured victim + 1.6 damaged vehicles b. 1 serious accident → 1.5 seriously injured victims + 2.0 minor injured victims + 1.2 damaged vehicles c. 1 minor accident → 1.0 minor injured victim + 0.5 damaged vehicle d. 1 vehicle-damage-only accident → 1.4 damaged vehicles

For a particular year, if the number of fatal victims (based on hospital data) is 5,000, estimate the total accident cost.

REFERENCES 

Alfaro, J. M. Chapuis, and F. Fabre, eds. 1994. COST 313. Socioeconomic cost of road accidents. Report EUR 15464 EN, Brussels, Commission of the European Communities.



Andreassen, D.C. 1988. The application of cost data in traffic safety- Traffic safety theory and research methods. Netherlands, April.



Asian Development Bank (ADB). 1997. Road safety guidelines for Asian and Pacific Region. Regional Initiatives in Road Safety, Asian Development Bank.



Babtie Ross Silcock and TRL Limited. 2003. Guidelines for estimating the cost road crashes in developing countries. Final Report, Department for International Development Project R7780, Transport Research Laboratory, May.



Barrs, P., G. Smith, S. Baker, and D. Mohan. 1998. Injury prevention: An international perspective. Oxford University Press.



Department of Public Works and Highways (DPWH). 2003. Cost estimation and update handbook . Sixth Road Project. Capacity Building component. C08 Road Infrastructure

Safety Project, DPWH. 

Dessie, T.C. Lawson. 1991. The occurrence and driver characteristics associated with motor vehicle injuries in Addis, Ababa, Ethiopia. Journal of Tropical Medicine Hygiene 94:395-400.




Garber, Nicholas J., and Lester A. Hoel. 1999. Traffic and highway engineering. Second ed. brooks/Cole Publishing Co,



International Road Traffic and Accident Database (IRTAD). 1998. Special report, definitions and data availability. OECD-RTR Road Transport research P rogramme.



Jacobs, G. 1995. Costing road accidents in developing countries. Overseas Road Note 10. Crowthorne, Berkshire: Transport Research Laboratory.



Jacobs G., A. Aeron-Thomas, A. Astrop. 2000. Estimating global road fatalities. TRL Report 445, Transport Research Laboratory, Crowthorne, Berkshire.



Lamm, Ruediger, Basil Psarianos, and Theodor Mailaender. 1999. Highway design and traffic safety engineering handbook. McGraw-Hill.

 

Melhuish, C. 2001. The first GRSP ASEAN Seminar, March, Tokyo. National Epidemiology Center (NEC). 1998. Philippine health statistics. NEC, Department of Health Philippines.



Organization for Economic Co-operation and Development. 1981. Methods for evaluating road safely measures. OECD Road Research Group Report, June.



Pline, J. L., ed, 1992. Traffic engineering handbook. Fourth Ed. Washignton, D.C.: Insitiute of Transportation Engineers and Prentice Hall Inc.



Robertson, H. Douglas, ed. 2000. Manual for transportation engineering studies. Washington, D.C.: Institute of Transportation Engineers and Prentice-Hall Inc.



Sigua, R. 2000. The state of road safety in the Philippines. Journal on Public Policy. Quezon City: UP Center for Integrative and Development Studies and the University of the Philippines Press.

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Tanner, J.C. 1956. Accidents before and after the provision or removal of automatic traffic signals. RRL Note. No. 2887.



Traffic Management Group (TMG). 2002. Report of traffic accident statistics.



Trinca, G. W., Johnston, I., B. J. Campbell, F.A. Haight, P. Knight, M. Mackay, A. J. McLean, and E. Petrucelli. 1988. Reducing traffic injury: A global challenge. Melbourne: Royal Australasian College og Surgeons.



Vibal, T. 2003. Traffic accident analysis through hospital records. Master’s thesis, College of Engineering, University of the Philippines Diliman, Quezon City.

8: INTRODUCTION TO TRAVEL DEMAND FORECASTING

8 INTRODUCTION TO TRAVEL DEMAND FORECASTING

8.1 INTRODUCTION

This chapter introduces the classic four-step forecasting model which was developed more than sixty years ago in the United States. The method has deficiencies, and other new ones have been developed over the past ten years. However, the method is still widely used as a tool over analyzing travel demand and estimating future traffic flow. Most commercially available software for forecasting travel demand are still largely based on this four-step model. It provides a tool for traffic engineers and planners to analyze travel demand and traffic situation in a given stud y area. Prior to the application of the four-step model, it is always necessary to obtain as much information as possible on the socioeconomic indicators of the area under study, such as population, income distribution, car ownership, etc. Using statistical tools, these socioeconomic variables may be forecasted within the planning horizon, which may vary from twenty to fifty years.

8.2 THE FOUR-STEP FORECASTING MODEL

The classic forecasting model has the following submodels: a. Trip generation and attraction b. Trip distribution c. Modal split d. Traffic assignment In a nutshell, the use of these models follows a logical order as shown in figure 8.1. The models answer basic questions that determine the number of future trips, the origins and destinations of such trips, the modes of transportation used, and the routes taken by these trips. The data are necessary for planning new infrastructure facilities, or expanding existing ones.


8.3 THE ORIGIN-DESTINATION TABLE (OD MATRIX)

Once the study are is defined, it is divided into a number of zones normally defined by political or administrative boundaries. These are called internal zones. Depending on the coverage of the study, a zone may correspond to one barangay, town, or city. The study may also consider some zones outside the study area, which may greatly affect the trip patterns, These are called external zones. For example, If Metro Manila is taken as a study area, there is a need to consider the outlying areas of Cavite, Laguna, Rizal, and Bulacan, among others. For a more systematic analysis and easier presentation, an origin-destination (OD) table is generally prepared. The origin-destination table simply shows the trips from one zone to another within a given study area. The terms are defined in reference to figure 8.2.


The number of trips O i , generated from zone i is given by



 = �

(8.1)

=1

This is also referred to as trip generation. It is obtained by summing up all the entries in a given row i. The number of trips D j attracted to zone j is given by



 = �

(8.2)

=1

This referred to as trip attraction. It is obtained by summing up all the entries in a given column j. Trip production is defined in terms of either O i or D j :






 = � = � =1

(8.3)

=1

Sometimes the present trip production is estimated first before the trip generation and trip attraction are analyzed. Trip production is estimated as follows:

 = ( ′_, _, … )

(8.4)

The independent variables inside the parenthesis must be selected to satisfy the following requirements: a. Predictability Trips per day at cities in the world are fairly stable, which is about 2.5. Mani la is about 2.3 trips per day while Davao City is about 2.4 trips per day.

b. Existence of significant difference between categories A simple example of category is gender – male or female. Males usually generate more trips per day. In Metro Manila, this is about 2.6 for males compared with 2.0 females (ALMEC Corp. 1999).

8.4 METHODS FOR ESTIMATING TRIP GENERATION AND ATTRACTION

A number of methods are available for estimating trip generation and attraction. The more commonly used ones may fall under any of the following: a. Growth rate method b. Category analysis c. Regression model

8.4.1 Growth Rate Method The number of trips is assumed to be influenced by several variables like population, car ownership, or income. If future values of these variables can be estimated statistically, then the future number of trips may be based on the growth rates of these variables and may be estimated as follows:


8.4.2 Category Analysis Let us say that the number of cars is considered the main variable in determining trip making in a certain area. Based on the present number of households and trip making activities, the future trips can be estimated as follows: Suppose the following table shows the current condition based on interviews:

Number of cars/households Family Size

1 2 3 More than 3

1

2

No. of households 100

No. of trips 200

No. of households 50

No. of trips 150

200

500

100

350

150 50

450 200

50 10

200 70

From these data, the average trip generation rate per category can be estimated by dividing the number of trips by the number of households in each category.


Family size

Number of cars/households

1 2

1 2.0 2.5

2 3.0 3.5

3 More than 3

3.0 5.0

4.0 7.0

These trip generation rates are then applied to the forecasted number of households per category to obtain the future trip generation.

Example 8.1 The city of Vigan had the following land use activity statistics during morning peak hour in 2000. Estimate the total trip generation during th at period.


Solution: Estimated person trips can be computed by multiplying column a with column b.

The table summarized the total trip generation. Residential units produce about 20,000 person trips in the morning. Trip attraction to various establishments is also obtained by considering all person trips coming in during the morning peak hour. It must be noted that total trip attraction does not equal total trip production because there are trips coming from outside the city of Vigan.


8.4.3 Regression Analysis The different indices or dependent variables normally considered that may have influence on trip making are shown in table 8.1.

In the Metro Manila Urban Transportation Integration Study (ALMEC Corp 1999), the following trip generation and attraction models are utilized:



 = �  +  =1

(8.6)


8.5 TRIP DISTRIBUTION

Again, the objective of this model is to determine from which zones these trip generations (O i ) are generated and to which zones these trip attarctions (D j ) are bound. A number of models have been developed in the past to distribute trips and these are classified as follows: a. Present pattern method b. Model method

8.5.1 Present Pattern Method Some of the methods under the first category are the following: a. Uniform factor method

b. Average factor method

c. Detroit method

The principle behind this method is that trip distribution is proportional to growth rate of trip generation


and that trip distribution is proportional to the relative growth rate of trip attraction to trip production

d. Fratar method This is the most commonly used present pattern method.

Some of the disadvantages of the present pattern method are the following: A. Complete OD matrix is required. B. Change of land use is not considered; where the present trip distribution is zero, future is also zero. C. If there is error in current OD matrix, the error is exp anded with the same rate.

8.5.2 Model Method A number of model methods are patterned after Newton’s law of gravitation. Hence, these are termed gravity models.


a. Basic type of gravity model

Other forms of resistance functions are:

in general, the basic type may be written as:

b. Bureau of Public Roads type gravity model

c. Voohees type gravity model

Some of the merits cited for the gravity models are as follows: a. Trip resistance is considered b. Structure of model is easy to understand. c. Complete OD matrix is not necessarily required.


The demerits, however, are as follows: a. Reasoning is not clear why human behavior is related to Newton’s gravity law. b. Index of resistance is arbitrary. c. Trip distribution within zone is difficult to treat. d. Trip distribution for near zone pairs tends to be larger than real values and vice versa.

8.6 MODAL SPLIT

Calculation of choice ration may be done using either binary or multiple ch oice. Under the method of multiple choice, all possible modes are identified and the share of each mode is calculated. The use of binary choice is relatively easy compared to multiple choice. Figure 8.3 shows the sequence of modal choice following a binary tree procedure.

8.6.1 The Generalized Cost The generalized cost attempts to put costing on quantifiable and sometimes unquantifiable costs that may be incurred during a trip using a specified mode. Two cost items ma y be quantified easily: cost (in ordinary sense, such as fare when taking public transport) and travel time. Level of service may be included in the generalized cost but there is difficulty in q uantifying it.


Considering several competing modes, the mode that will have the least generalized cost will be chosen. Supposing that there are two modes, with corresponding generalized costs:

The shares of trip makers likely to use modes 1 and 2 are shown by the areas of the time value distribution in figure 8.4


One disadvantage of the generalized cost method is the difficulty in determining the distribution of time value. It is also difficult to treat more than two modes.

8.6.2 Disaggregate Choice Model This method originated from microeconomics. It assumes that a person will use a p articular mode with maximum utility for him. Consider two modes l and m, then


Example 8.2 A calibrated utility function for travel in a medium-sized city by car, bus, and light rail is U = a -0.02X1 – 0.05X 2 Where X 1 is the cost of travel in pesos and X2 is the travel time (min). Calculate the modal split for the given values: Mode Car Bus

A -0.3 -0.38

X1 30 8

X2 25 38

Light rail

-0.32

15

30

If a parking fee of P30 per trip is imposed, what would be the split to the other two modes?

Solution:

Similarly, P bus and P light

rail

can be obtained using the same formula. The

calculations are summarized in the table below. The current modal share shows that car and light rail have almost the same share. Mode Car

U -2.15

eu 0.1164

P 0.3598

% 36

Bus Light rail

-2.44 -2.12

0.0871 0.1200

0.2692 0.3708

27 37

0.3236

1.00

100

Total

Now, when a parking fee of P30 is imposed to each traveller, the utility of car will be reduced as follows: U c = -0.3 – 0.2(6) – 0.05(25) = -2.75


Probabilities are recomputed and the results are sho wn below.

The share of car is greatly reduced from 36 percent to 24 percent, an overall reduction of 33 percent. This results in car users shifting to bus and rail, which now have an increased share of 32 percent and 44 percent, respectively.

8.7 ROUTE ASSIGNMENT

Given a road network, car drivers will normally use the route or routes through which they will reach their destination in the least time or distance. The same assumption is used to assign trips or vehicles in the four-step model. The road network is usually drawn using nodes and links as shown in figure 8.5. The zone centroids are represented by nodes, and the roads connecting the zones are presented by links.


8.7.1 The Shortest Path A prerequisite to route assignment is the determination of the shortest path from one node of the network to another. Given a road network with known characteristics such as distance or travel time, the shortest path may be found using Dijkstra’s algorithm. The algorithm or procedure follows these basic steps:

a. First, label the staring node with a value equal to 0. This label is permanent as this will not be changed. b. Consider each node adjacent to this node and give them temporary labels. (Only those without permanent labels are considered.) i.

If a node is unlabelled, it is given a label equal to the weight of the link plus the value of the previously labelled node.

ii.

If a node is labelled, calculate the value of the label and, if this is less than the current value, then exchange its value with the smaller one; otherwise, leave the label unchanged.

c. Choose the node with the smallest temporary label and make the label permanent. d. Repeat steps b and c until the final node has been given a permanent label. The shortest path has a length given by its permanent value.

Dijkstra’s algorithm will be illustrated by an example.

Example 8.3 Consider the road network shown in figure 8.6(A). The nodes are labelled a to k . The links have values in travel time in minutes. Determine the shortest path (least travel time) from a to k using Dijsktra’s algoritm.

Solution: Node a is given a permanent label with value equal to 0. From a, adjacent nodes are temporarily labelled as shown in (B). With 2 as the smallest, node b is permanently labelled as shown in (C). From node b, adjacent nodes are temporarily labelled. Again the node with the smallest value is chose. Note that either node c or e may be chosen because they both have values


equal to 3. Node c is chosen in this case, and unlabelled nodes adjacent to it are labelled temporarily as shown in (D). The steps are repeated. It will be noted in (E) that the value 13 is replaced by a smaller value, which is 11.


It takes steps (A) to (L) to label all the nodes completely. Finally node k is labelled permanently. The shortest path from node a to k follows the route a-e-g-j-k with a total travel time of 23 minutes.


8.7.2 Network Assignment Given choices or routes, it is but natural to assume that the trip makers will consider the route that would require the least time or least distance. Based on this assumption, the methods used to assign the trips within the road network are the following: a. All-or-nothing assignment b. Constant assignment ratio c. Incremental assignment

All-or-nothing assignment Considering one OD pair, all trips are assigned to the shortest path from point of origin to point of destination. After these trips are loaded into the network, the level of service of the roads in the network may change. The basic steps in conducting an all-or-nothing assignment are as follows: a. Find the minimum path between zones i and j. b. Assign all trips T iy the minimum path. c. Repeat steps 1 and 2 for all OD pairs.

Constant assignment ratio In this method, it is assumed that the number of trips assigned to a route is inversely proportional to the travel time or cost of that route, i.e., more trips will be assigned to a route providing shorter travel time or lesser cost. The basic steps for the constant assignment ratio method are as follows: a. Find out several possible routes between zones i and j. b. Calculate the level of service (time or cost) on each route. c. Divide the distributed trip to each route inversely p roportional to LOS. d. Repeat for all OD pairs.

Example 8.4 Suppose that 100 trips are to be distributed among 4 routes with the following travel times. Assign these trips using constant assignment ratio.


Route 1

T, hrs 1.0

2 3

1.25 1.5

4

2.0

The inverse of time for each route is computed. This serves as the level of service of the route. The assigned trips to each route are obtained in proportion to this LOS. Higher values would have larger share of assigned trips. The result of assignment is shown in the table below. Route 1

I/T 1.00

Assigned trips 33.71

2 3 4 Total

0.8 0.67 0.50 2.97

26.97 22.47 16.85 100.00

Incremental assignment This method considers the influence of previously assigned trips. It is based on the Wardrop’s Princicple, which states that out of several routes available between zones i and j, the routes that are used have equal level of service. The routes that are not used have lower LOS. Consider the trips originating from one zone to be assigned. The incremental assignment method takes the following steps: a. Assign 1/n of the trips to route (by using all-or-nothing assignment or constant assignment ratio). b. Calculate the new level of service for the state that 1/n trips are already assigned. c. Assign next 1/n trips. d. Repeat until all trips are assigned.


PROBLEMS

1. Use gravity model (Voohees type) to distribute the person trips given below. Refine the method using Fratar iteration scheme. (Stop iteration when row and column are 1 ±0.05.)

2. A multinomial logit mode choice model is calibrated for 10,000 persons. The resulting utility function is given below:

For a particular OD pair, three modes are available, with characteristics as follows: Mode

Car Aircon bus

Out-of-pocket cost, pesos 50

Jeepney

Travel time,min

10

30 45

5

50

Determine the following: a. Percentage share of each mode b. No. of vehicle of each mode

Ave. occupancy persons/veh 2

40 14


3. Assign the vehicle trips in the given network below using all-or-nothing assignment. Use Dijkstra’s algorithm to find minimum paths.

4. Determine the shortest path from a to b using Dijkstra’s algorithm.


5. Assign the given vehicle trips (veh.hr) using incremental method (n = 3).

Apply the capacity restraint relation shown below:


6. Assign the peak hour vehicular trips shown on the given road network. Use all-or-nothing assignment for the first 1/n trips, then use incremental method with capacity-restraint for the succeeding assignments (n = 2).

7. Given the following data: a. Present person trip OD table


b. Growth Factors:

c. Calibrated utility function:

d. Cost of travel (pesos) and travel time in minutes. Use for modal choice only. (Assume data for 1 to 2 are the same for 2 to 1, etc.)


e. Estimated travel time in each link:

Perform: i.

trip distribution using Fratar method (make 1 iteration only, i.e., get one set of row and column factors)

ii.

modal split using logit model

iii.

trip assignment of cars only using all-or-nothing assignment

(Average veh, occupancy: car – 1.5 persons; Jeepney = 14.0 persons)

REFERENCES



ALMEC Corporation. 1999. Metro Manila urban transportation integration study (MMUTIS). Project final report, December.



Garnier, Rowan, and John Taylor. 1992. Discrete mathematics for new technology. Adam Hilger.



Khisty, C. Jotin, and B. Kent Lall. 1998. An introduction to transportation engineering. Second ed. Prentice-Hall.



Mannering, Fred L., and Walter P. Kilareski. 1990. Principles of highway engineering and traffic analysis. John Wiley and Sons.



Morlok, Edward K. 1978. Introduction to transportation engineering and planning. New York: MCGraw-Hill Book Company.



Salter, R. J. 1976. Highway traffic analysis and design. Revised edition. MacMillan Press.



Wardrop, J. G., 1952. Some theoretical aspects of road traffic research. Proceedings, Institution of Civil Engineers, part 2, vol. 1, 325-7 8. London.

9: INTRODUCTION TO INTELLIGENT TRANSPORTATION SYSTEM

9 INTRODUCTION TO INTELLIGENT TRANSPORTATION SYSTEM 9.1 INTRODUCTION

Intelligent Transportation System (ITS) is the application of information and communication technologies to surface traffic and transportation systems. ITS has the potential to improve mobility and operation of transportation system. Deployment of ITS usually falls under any of the following nine areas (HIDO 2000):

a. Advances in navigation systems b. Electronic toll collection c. Assistance for safe driving d. Optimization of traffic management e. Increasing efficiency in road management f. Support for public transport g. Increasing efficient in commercial vehicle operations h. Support for pedestrians i.

Support for emergency vehicle operations

Based on the experience of several countries that have earlier deployed ITS, some of the estimated benefits are the following (US DOT 1998): a. Advanced traffic surveillance and signal control systems have resulted in travel time reduction ranging from 8 percent to 25 percent. b. Electronic fare payment technologies for transit systems have resulted in increased revenues 3-30 percent due to fewer evasions. c. Incident management programs can reduce delay associated with congestion caused by incidents by 10-45 percent.


d. Electronic toll collection increases capacity by 200-300 percent compared to attended lanes. e. Widespread use of Mayday emergency notification devices can reduce the time it takes to discover a rural crash from 1 minute to 9.6 minutes.

9.2 CURRENT DEPLOYMENT OF ITS IN THE PHILIPPINES

9.2.1

Traffic-Responsive Signal System

The State-of-the-Art Metro Manila Adaptive Responsive Traffic (SMART) system is a signalling project undertaken by the Department of Public Works and Highways-Traffic Engineering Center (DPWH-TEC) for the upgrading and development of traffic signals in Metro Manila. The SMART Project utilized the Sydney Coordinated Adaptive Traffic System (SCATS) technology. As a dynamic demand-responsive traffic system used for area-wide control, the signal timings are free to evolve in response to detected traffic demand. The SCATS was successfully installed for the first time in the country in Cebu City. Figure 9.1 shows the system’s configuration when used over a wide area such as a big city or metropolis. Areas covering a number of intersections are controlled by a regional computer, which is then connected to a central management computer (CMC). A typical sample display of a regional or central management computer useful for assessment of traffic condition is shown in Figure 9.2. It shows the congestion level of the road network in Cebu City.

Initial assessment


There is a tendency to assume that once a new traffic control system replaces an older one, traffic flow will automatically improve – speeds will increase quieting will be less, traffic will be orderly, etc. However, there are a number of factors external to the system that may severely affect the traffic flow. In a “before-and-after” study conducted to evaluate the system, it was observed that most of the unwanted practices noted during the before case were still prevalent during the after case (UP NCTSFI 2001). These include •

uncontrolled loading and unloading of passengers by PUVs;

•

illegal parking;

•

vendors occupying sidewalks (even carriageway), leaving pedestrians no option but to use the road;

•

commuters on the road waiting for rides; and

•

laxity in traffic enforcement.

These practices severely hinder the flow of traffic along some thoroughfares considered in the study – Taft Ave., Mabini St., and Del Pilar St. There is no way that SCATS alone can solve the traffic problems along these roads. A concerned effort by concerned authorities is therefore necessary to eliminate these practices. Otherwise, the government’s effort to alleviate congestion through the use of advanced technologies will be worthless.


Nevertheless, the SCATS has been found to manage traffic better by preventing extreme peaing (or concentration) of the traffic volumes, thus allowing the available capacities to be used more optimally. With regard to queuing, twenty-five intersections along four corridors (i.e., Taft Avenue, Roxas Boulevard, Mabini St., and Del Pilar St.) were evaluated before and after the installation and operation of the SCATS traffic signal system. An overall reduction of 30.39 percent was estimated four queue lengths during the morning peak. Similarly, an overall reduction of 35.98 percent was estimated for afternoon peek queues. These reduction clearly indicates an improvement due to the installation and operation of SCATS.

9.2.2 The Metro Manila ETC Systems Dubbed E-Pass, the first-ever electronic toll collection (ETC) system in the Philippines started to be implemented in August 2000. Transcore US and Transcore Australia take care of software and hardware, respectively. E-PASS is expected to be used in more than 150 toll lanes along the South Luzon Expressway (SLEX and the Skyway (elevated expressway). In this system, a tag is placed on the inside surface of the windshield behind the vehicle’s rear-view mirror. The tag is electronically read at the entry and exit of E-Pass ready toll lanes. Upon exit, it is read to determine the toll fee to be paid. If here is enough balance in one’s E-PASS account, a green light is given and the barrier lifts up. (A yellow light is also given to alert the subscriber that his or her prepaid toll balance is below P250 and that it would be advisable to reload soon. A red light means a zero balance account, meaning the subscriber cannot use the e-pass lanes to exit.) The tag is available at the customer service center and through sixteen participating Shell service station located near expressway. A “one tag, one vehicle” policy is applied, which means a motorist is not allowed to switch the tag to any other vehicle if he or she owns more than one. The total cost of enrolling in the ETC system is P3,800 for each tag kit. It includes the five-year lease for the tag. To encourage motorists to subscribe to the new system, a 60 percent discount was offered for the first 10,000 tag kits. Cash lanes that are not included in the E-PASS service are also computerized for a faster cash collection system. Cash value cards are available through interactive kiosks in Shell stations. Figure 9.3 shows the different components of SLEX ETC System.


Features of the SLEX ETC System a. Automatic vehicle classification •

AVC system classifies vehicles using height and number of axles.

•

Done at exit points (exit lanes).

•

Done for both manual and ETC payment.

Figure 9.4 shows the various devices and components of a toll gate (E-PASS exit).


b. Cash collection •

Uses magnetic striped card which is encoded by the toll teller and handed to the patron at entry booth,

•

Card is electronically “read” at the exit booth.

•

Toll teller classifies the vehicle/AVC system makes its own classification independently.

•

Toll is computed by the computer and displayed to the toll teller and the patron.

•

A motorist receipt is generated.

c. Electronic toll collection •

All lanes with ETC antenna can be switched to “ETC only” lanes (figure 9.5).

•

Patrons use tags.

•

A siren and an amber flashing light will provide violation notification to staff:

•

-

orange → low balance

-

red → insufficient fund

If fund is insufficient, the patron has to pay in cash.

d. Information generated at the supervisor’s level (maxi booth) •

Lane information, such as lane number, lane direction, lane mode, operator, payment type, etc.

•

Transaction details at a particular lane – vehicle classification, amount paid, etc.

•

Unusual occurrences, such as changes in lane modes, toll operator log on/off, violation, nonrevenue transaction, equipment fault or recovery.

•

Assignment of cash bags


Initial assessment The existing system lacks some of the features of a full-blown ETC system found in other countries. There is no monitoring system using cameras or automatic vehicle violation processing system. To cut cost, a simplified system was devised so that full control is done within the jurisdiction of the expressway. The existing ETC system requires motorists to slow down or to come to a full stop for checking. A horizontal barrier lifts when a green light is given. At times, when traffic becomes heavy, a bumper-to-bumper situation can cause the barrier to rise and fall too often. This can confuse drivers who follow light and barrier. This technical flaw needs to be addressed since in 2001, at least 200 barriers were destroyed every month, not to mention damages to vehicles. Minimum spacing or headway between vehicles should b e enforced. A simple method is to paint two lines before the toll gates for checking the spacing. Based on an initial study of the operation of the tollway, the dedicated E-PASS lane has an average tollbooth transaction time of 1.15 seconds per vehicle compared to 15.0 seconds per vehicles for the manual scheme (cash coupons), and 5.9 seconds per vehicles for mixed-mode lanes (Padayhag and Sigua 2001). Table 9.1 shows the lane usage and service rates at Nichols A tollgate.


Table 9.2 shows he number of vehicles using the dedicated E-PASS lanes at Nichols and Bicutan during peak hours. At Nichols A, 13.6 percent of the vehicles using the tollgate are EPASS users. a. Morning peak (7:30 – 10:30 AM)

b. Afternoon peak (4:00 – 6:00 PM)


The SLEX ETC system is a distance-based system. Overall, the trip demand on the use of the expressway is basically the same. It is worth looking at the system as time-based, with higher fees collected or charged during peak hours. The concept of time-based fee charging is discussed in the next section. After major rehabilitation of the North Luzon Expressway (NLEX), the Manila North Luzon Tollways Corporation began full operation of ETC in early 2005. (See figure 9.6) Dubbed EC-Tag, the ETC and NLEX operates at the same frequency (DSRC 5.8 Ghz) similar to SLEX. Among the features of the new NEX are computerized toll collection system; dedicated lane for transponder and swipe card system for faster transactions; reliable emergency and roadside services; including smart emergency phone boxes; and twenty-four-hour emergency assistance consisting of telephone operators, traffic patrol teams, first air emergency trucks and tow trucks.


Table 9.3 shows a comparison of the SLEX and the NLEX ETC systems. The estimated percentage of ETC users was for the year 2006.

9.3 ROAD PRICING

Koshi’s assessment of the traffic congestion in Manila, Bangkok, and Jakarta made him conclude that the only effective method available in Asian cities is “road pricing” (Koshi 1996). Fees have to be set unrealistically high to achieve a meaningful reduction in overall demand. Its primary objective should be to encourage drivers to reconsider their time of departure and time of return. As a secondary benefit, the revenue generated from it can be used for building public transit networks such as bus and rail transit systems. However, he also stressed that unless adequate transportation infrastructure is built, the problem will not be solved no matter what amount of time or money is present on information processing and communication. The first priority, therefore, is to build rail transit system.

9.3.1 Time-Bases Fees The present distribution of trip with time (arrival and departure) is one of the causes of congestion in Metro Manila. Trip making is concentrated in a short period during peak hours as shown in figure 9.7. A better spread of the time of arrival to a longer interval will contribute to the alleviation of traffic congestion. Road pricing does just that by charging any vehicle entering the restraint zone a fee, depending on the level of congestion in the area.


9.3.2 Phasing in Peak-Hour Road Pricing No system for peak-hour road pricing can be installed all at once in a large metropolitan area; it would have to be phased in gradually. The first locations chosen would be road or other sites (such as bridges) that are heavily congested during peak hours and have no easy substitute routes. Another possibility would be “zone pricing”, like that in downtown areas. Special fees would have to be paid for vehicle entry during key hours in one or a few heavily congested zones – such as central business districts (CBDs). Vehicles entering these zones then would either pay monthly fees computed by an automatic vehicle identification (AVI) system – or buy stickers that would exempt them from arrest and fines – as in the original Singapore system (monitored by human spotters). Zone pricing would work best where congestion is heavy in a relatively limited and compact area rather than over a broad region. Since many drivers diverted from priced roads would switch to alternative routes, traffic would rise sharply on these alternative routes. This could offset much of the advantage of the reduced congestion on toll routes if the system leaves many such alternatives untolled. Peak hour pricing would probably never be installed on all alternative routes, even after an entire system had been phased. Of course, modern technology changes so quickly that some method of doing this


might be found. Nevertheless, increases in traffic or alternative routes might become an almost permanent condition in the near future. Heavy traffic might therefore be diverted into residential neighbourhoods or onto other socially undesirable routes. An important question is: How high should the new road charges be? These should be high enough to divert the minimum number of vehicles needed to achieve desired average speeds, but not so high that surrounding roadways become clogged because so many vehicles have had to be diverted. Choosing the right tools will therefore be a matter of trial-and-error experimenting on each road. Coping with the traffic that shifts to alternative routes that do not charge tolls poses a challenge.

9.3.3 Other Effects of Peak-Hour Road Pricing Peak hour road pricing would also increase the peak-hour use of public transit because some commuters would find driving more costly than using public transit after taking into account the time, toll, and operating expenses. Furthermore, more commuters who usually drive alone would start ride sharing, for some same reason. Both these effects would reduce peak hour congestion.

9.3.4 MMUTIS Studies on road Pricing A number of hypothetical cases have been studied for the application of road pricing in Metro Manila, although its political and social acceptability is still uncertain (ALMEC Corp 1999): a. Road pricing in an arterial EDSA, the most important circumferential road in Metro Manila, was considered for road pricing. It was assumed that all the private vehicles entering EDSA pas US$ 1 per entry. The traffic crossing EDSA is not charged. Results showed the following: i.

Alleviation of congestion by about 5 percent along EDSA. Some parallel roads, however, became congested due to detouring traffic.

ii.

Potential revenue of about US$ 70 million per year.

b. Cordon pricing within a CBD Cordon pricing was tested for the CBD of Makati City, the business center of Metro Manila. A similar fee of US$ 1 was assumed.


i.

The effect of reducing traffic congestion is significant in and around Makati (510 percent).

ii.

Potential revenue estimated at US$ 61 million per year.

c. Cordon pricing within a bigger area A much bigger area bounded by the circumferential road EDSA was considered. i.

Most of the roads in Metro Manila show an alleviation of traffic congestion by 3-10 percent.

ii.

Potential revenue estimated at US$ 174 million per year.

d. Parking pricing Parking pricing within the CBD of Makati City was assumed. A parking pricing charge of about US$ 1 per parking event was applied. i.

Effect on alleviation minimal.

ii.

9.3 SOME

Potential revenue about US$ 15 million per year.

ISSUES

RELATED

TO

SUSTAINABLE

DEPLOYMENT

OF

ITS

DEVELOPING COUNTRIES

a. Institution Success ITS deployment requires a very high level of cooperation between national and local agencies on the one hand, and law enforcement and emergenc y response agencies on the other. Since these agencies do not normally work closely together, significant turf and organizational culture problems may arise. Traditional transportation agency leaders also suffer from inadequate knowledge of ITS technologies and their potential benefits.

b. Infrastructure Successful ITS deployment and operations require basic infrastructure elements like a well-developed communications backbone and uninterrupted power supply.


c. Technology Understanding the role of ITS technologies is critical to its success. ITS planning and design should be based on “needs-based assessments”, not just on technology push.

d. Finance/budget Although IS deployments cost significantly less than new road construction, they involve allocation of funds to be spent on systems unfamiliar to transport authorities, or which have not been deployed widely elsewhere. This creates a situation of inadequate support for ITS projects, especially, since several transport authorities cannot even afford basic highway maintenance and rehabilitation.

9.4 CONDITIONS FOR ACCEPTABLE DEPLOYMENT/ IMPLEMENTATION OF ITS IN METRO MANILA

A truly working ITS scheme, such as Electronic Road Pricing (ERP) or ETC, is one that has the right objectives, delivers its predicted benefits, and is acceptable to the ones paying for it. This means that when an ITS scheme is successful, the ones paying for it have to enjoy some of its benefits. Something that works in Singapore may not work in Manila. Cultures differ greatly. Charging for something that used to be free may not be a good approach. A number of ITS schemes such as ERP will never succeed as long as the victims of the current problems feel they have to pay for becoming a victim in the solution. There is already a growing criticism that ITS favors the rich. Expected beneficiaries of ITS should not be only car users. Metro Manila is a good example when it comes to public transport patronage. About 70 percent of trip makers rely on public transport. It should be the policy of the government that revenues from ITS schemes (ETC or ERP) be earmarked for transportation infrastructure development, such as mass transit systems, instead of simply going to general funds. Unless ITS is geared toward mass transportation system, it is likely to fail in developing countries where majority of trip makers rely on public transport for mobility.


9.6 CONCLUSION

ITS should complement the government’s plans and programs to build more urban expressways and urban rail networks. Preparations for planning and deployment of ITS – such as full-blown ETC along expressways or major arterials. ERP for CBDs and, automation at LRT/MRT stations – should begin now. Urgent tasks to be done are the following: •

Creation of an official organization to look at ITS priorities.

•

Development of ITS master plan for Metro Manila. Priority should be given to mass transport-related ITS application. There is also the growing concern on safety and environment issues.

•

Comprehensive analysis of the first examples/initiatives of ITS deployment in Metro Manila – SCATS signal System and Skyway’s ETC – their effectiveness, and what went wrong. Is SCATS a failure due to lack of complementing traffic management measures? Do ETC’s partial implementation and cost-cutting measures make the system ineffective? Is full implementation an absolute condition?

•

Making it known that ITS is not only for developed countries. ITS seems to be so sophisticated/high-tech that it becomes incomprehensible to traditional politicians. In a developing country, there is a strong tendency to rely heavily on manual methods due to cheap labor. This is also true on the Philippines where manual method is thought to be more effective than automatic means.

•

As government is desperately looking for effective solutions, a lot of convincing is needed for the decision makers to believe that ITS is not simply a “technology push” but a viable solution to Metro Manila’s congestion problem.

REFERENCES 

ALMEC Corporation. 1999. Metro Manila urban transportation integration studies (MMUTIS). Project final report, December.



Highway Industry Development Organization (HIDO). 2000. Intelligent transport systems. ITS handbook 2000-2001. Japan.



Koshi. M. 1996. Traffic congestion in Asian cities: The wheel extended. A Toyota Quarterly Review, no. 95.




Padayhag. G. U. and R.G. Sigua 2001. Evaluation of electronic toll collection (ETC) system along South Luzon Expressway and Manila Skyway. 9th Annual conference, Transportation Science Society of the Philippines, Manila. July.



University of the Philippines National center for Transportation Studies Foundation Inc. (UP NCTSFI). 2001. Metro Manila SMART Traffic Signaling Project (SCATS) before and after study final report, June.



US Department of Transportation, 1998. ITS Joint Program, ITS for Metropolitan Areas.

GLOSSARY OF TERMS

AADT

Annual average daily traffic; it is estimated as the total volume counted over one year divided by the number of days in the year.

ADT

Average daily traffic; obtained by averaging traffic volume over a number of days at least 2 days and less than 365 days.

Blackspots

Hazardous or accident-prone locations

Broken back curve

A curve characterized by a short tangent between two sub-curves in the same direction.

Capacity

The maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic, and control conditions.

Channelization

Geometric improvement normally applied at intersections to simplify movements of vehicles to lead drivers to face one conflict at a time.

Clearance interval

The sum of yellow and all-red period in between phases.

Clothoid

A spiral that serves as a transition path as the vehicle enters or leaves a circular curve.

Compound curve

A two-arc simple curve having its centers on the same side of the common tangent.

Cordon counts

Counts used to determine the number of vehicles and/or persons entering and leaving an enclosed area.

Crest vertical curve

A vertical curve with the parabolic curve drawn below the two tangents

Critical gap

Describes the minimum gaps needed by drivers of minor road vehicles.

Cycle

One complete indication of green, yellow, and red signals.

D/D/1

A single-server queuing system with regularity of both arrivals and departures.

Delineators

Small reflective panels or buttons mounted on guide posts or guard fences as an effective aid for night driving.

Density

The number of vehicles in a given length of road at an instant point in time.

Design speed

The maximum safe speed that can be maintained over a specified section of highway when conditions are so favourable that the design features of the highway govern.

Dijkstra’s algorithm

A procedure used in route assignment stage of the four-step model to determine the shortest path from one node of the network to another.

Diplomatic vehicles

Motor vehicles by a foreign government or by their diplomatic officials in the Philippines.

Disaggregate choice model

A method used for determining modal split, which assumes that a person will use a particular mode with maximum utility for him.

Easement curve

See clothoid.

ETC

Electronic Toll Collection; an ITS application; see also ITS.

Expressway

A major divided highway designed for high-speed travel, having few or no intersections; also called freeway or limited access highway.

FIFO

First-in First-out, i.e., the first one that arrives at the service station gets served first and therefore is the first to leave the system as well.

Flow Rate

The number of vehicles passing a point during a specified period of time.

For hire vehicles

Motor vehicles authorized to be used as public vehicles by virtue of a franchise granted by the Land Transportation Franchising and Regulatory Board.

Generalized cost

A term that puts costs on quantifiable and sometimes unquantifiable costs that may be incurred during a trip using a specified mode.

Glass beads

Materials used to enhance the wet-night reflectivities of pavement markings.

Grade-separation

Eliminates the problematic crossing conflicts of the different movements of vehicles; flyover/overpass, underpass, or full-blown interchanges are some of the examples.

Greenshield’s model

A traffic flow model describing linear relation between speed and density.

Harmonic mean speed

See Space mean speed.

Intergreen

See Clearance interval.

Interrupted flow

Flow occurring at intersections or driveways where vehicles are required to stop by any cause outside the traffic stream such as traffic signs (STOP or YIELD), traffic signal lights, etc.

Intersection

The point where traffic flow converges and where direction of travel changes.

ITS

Intelligent transportation system; the application of information and communication technologies for surface traffic and transportation systems.

Jeepney

An indigenous mode of public transportation in the Philippines; a postwar creation, it was inspired by the GI jeeps that the American soldiers brought with them to the country during the 1940s.

Kendall’s notation

A notation used to describe queuing system.

Level of service

A qualitative description of how a certain facility is performing.

LIFO

Last-in first-out; i.e., the last one that gets in gets our first, See also FIFO

M/D/1

A single-server queuing system which assumes that the arrivals of vehicles follow a negative exponential distribution, a probability distribution characterized by randomness. Departure is assumed to be regular as in the D/D/1. (See also D/D/1.)

M/M/1

A single-server queuing system that assumes negative exponential for both arrival and departure distributions. (See also M/M/1).

M/M/N

A multiple-server queuing system that assumes negative exponential for both arrival and departure distributions. (See also M/M/1).

Maximum speed limit

The 85 percentile speed used for speed regulation.

Minimum speed limit

The 15 percentile speed used for speed regulation.

Modal split

A part of the four-step model with the objective of determining which mode of travel is used by a trip maker.

Moving observer method

A method developed by the Transport Road Research Laboratory in the UK that is used to obtain information on traffic volume, speed, and density of a given section of road.

Official/government

Motor vehicles owned by the Philippine government.

t t

vehicles Offset

The difference in the start of green of two signalized intersection.

Parabolic vertical curve

Curve used for the design of the profile of highways.

Passing sight distance

The shortest distance required for a vehicle to safely pull out of a traffic lane, pass a vehicle traveling in the same direction and return to the correct lane without interfering either with the overtaken vehicle or opposing traffic.

Pavement markings

Traffic control devices that take the form of lines, symbols, messages, or numerals and may be set into the surface of, applied upon, or attached to the pavement.

PCU value

Passenger car unit equivalent of the different types of vehicles.

Pedicab

A bicycle with a sidecar; nonmotorized mode of public transportation. See also bicycle.

Phasing

A process by which right of way is given to particular movements in a logical manner with the primary purpose of minimizing the number of conflicts.

Pneumatic rode tube

Used as detector, it senses vehicle pressure and sends a burst of air pressure along a rubber tube when a vehicle’s tires pass over them; the pulse of air pressure then closes an air switch and sends an electrical signal that marks the passage of a vehicle.

Private vehicles

Motor vehicles owned by private individuals or companies and are not intended to be used for hire.

Raised pavement markers

Small rectangular or dome-shaped devices that are fixed or embedded to the pavement to simulate or supplement painted pavement markings.

Reserve capacity

Difference between the existing traffic volume and available capacity.

Reserve curve

A two-arc simple curve having its centers on opposite sides.

“Right of Way” rule

Rule which states that when two vehicles arrive at the same time at the intersection, the vehicle on the right has the priority.

Road pricing

A method of alleviating congestion by charging any vehicle entering the restraint zone a special fee to depending on the level of congestion in the area.

Rotary

A form of unsignalized intersection in which all the vehicles move counter clockwise in one-way fashion.

Roundabout

See rotary.

Route Assignment

A part of the four-step model which is used to assign trips or vehicles to a given road network.

Sag vertical curve

A vertical curve with the parabolic curve drawn above the two tangents.

Saturation flow rate

The maximum flow rate occurring at the stop line once traffic initially in queue is given green time indication.

SCATS

Sydney Coordinated Adaptive Traffic System; third-generation system in which the signal timings are free to evolve in response to detected traffic volumes and queues; the system installed in Metro Cebu and some parts of Metro Manila.

SCOOT

Split Cycle Offset Optimization Techniques; third-generation system in which the signal timings are free to evolve in response to detected traffic volumes and queues.

Screen line counts

Classified counts taken at some points along a line that bisects a given area.

Semaphore

A visual signalling apparatus with flags, lights, or mechanically moving arms, as one used on a railroad; used also for controlling intersections.

Shock wave

A phenomenon brought about by the motion or propagation of a change in density and flow.

Simple curve

A circular arc between two tangents.

Space mean speed

Speed based on the average travel time of vehicles in the stream within the section.

Spacing

The distance between two vehicles measured from the front bumper of one vehicle to that of another.

Spot speed

Arithmetic mean of the speeds of vehicles passing a point within a given interval of time.

Stopping sight distance

The shortest distance required for a vehicle traveling at the assumed running speed to stop safely before reaching a stationary object in its path.

Superelevation

Banking of the roadway necessary to counteract the centrifugal force that is acting on the vehicle.

Test car technique

A method for travel time studies that makes use of a test vehicle which is driven over the road section under study. The driver is instructed to travel at a speed that in his opinion is representative

of the speed of the traffic stream. Thermoplastic materials

Materials that can be heated to a liquid state, reshaped, and cooled to form a new object; regarded as the most successful of all pavement marking materials when properly applied.

Time headway

The time interval between passages of consecutive vehicles at a specified point on the road with a unit of time per vehicle.

Time mean speed

See Spot speed.

Time occupancy

The total time a detector is occupied divided by the total time of observation.

Traffic accident

An unexpected and undesirable event, especially one resulting in damage or harm.

Traffic control devices

Means by which the road used is advised as to detailed requirements or conditions affecting road use at specific places and times so that proper action may be taken and accident or delay avoided.

Traffic death

Defined by UN Organization (Geneva) as one that occurs within thirty days of the event.

Traffic engineering

That phase of transportation engineering that deals with the planning, geometric design, and traffic operations of roads, streets, and highways; their networks, terminals, and abutting lands; and their relationships with other modes of transportation.

Traffic management

A term used to embody the activities undertaken by a highway transportation agency to improve roadway system safety, efficiency, and effectiveness for both providers and consumers of transportation services.

Traffic regulation

Covers all aspects of the control of both vehicle (registration, ownership, mechanical fitness, accessories, size, and weight) and driver (age, ability to operate specific types of vehicles, financial responsibility).

Traffic signal

A visual signal to control the flow of traffic and pedestrians at intersections or at midblocks.

Traffic signs

Traffic control devices necessary to give information as to routes, directions, destinations, etc. Their function becomes more relevant when used to warn road users of hazards and in regulating any prohibitive action at specific places and/or at specified times.

Transportation engineering

A field or branch of civil engineering that deals with the application of technology and scientific principles to the planning,

functional design, operation, and management of facilities for any mode of transportation to provide for the safe, rapid, comfortable, convenient, economical, and environmentally compatible movement of people and goods. Tricycle

A three-wheel, motorized mode of public transportation consisting of a motorcycle with a sidecar. See also Pedicab.

Trip attraction

The number of trips that is attracted to a certain zone.

Trip distribution

A part of the four-step model with the objective of determining from which zones the trips are generated and to which zones these trips are bound.

Trip generation

The number of trips generated from a certain zone.

Two-way stop control

The major approaches without STOP signs have complete priority over the minor approaches with STOP signs.

Ultrasonic vehicle detectors Detect volume, presence, classifications and speed of vehicles; they are active acoustic sensors that transmit sound waves toward detection zones at a frequency ranging from 20 khz to 300 khz. U-turn scheme

A traffic management shcme in which intersections are replaced by U-turn slots. Operation is very similar to that of a roundabout except that it favors a particular road, which is assumed to be the major road.

Volume

See Flow rate.

11. Fundamentals of Traffic Engineering - Ricardo G. Sigua.pdf

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