Lectures of Highway Engineering

Highway Engineering

Lecture 1

Highway Route Location ‫نظام المحاضرات االلكتروني‬

Prepared by A.L Rawand Mohammed Badri

Contents  Introduction

 Steps in rout location  Principle of highway location

 Reconnaissance survey  Preliminary location survey  Final location survey

‫نظام المحاضرات االلكتروني‬

Introduction Alignment :-The position or the layout of the central line of the highway. – Horizontal alignment includes straight and curved paths. – Vertical alignment includes curves and gradients. The aim of alignment selection process is to find a location for the new road that will result in the lowest total construction, land, traffic and environmental costs ‫نظام المحاضرات االلكتروني‬

Steps in Route location Location of proposed highway is an important first step in its design and the steps as follow:

1- known the termini point 2-identify and locate 3-reconnaissance survey 4-draw a corridor 5-possible center line 6-examine each of the alternative alignment 7-final design ‫نظام المحاضرات االلكتروني‬

Principles of Highway Route Location Process • The basic principle for locating highways is that roadway

elements such as curvature and grade must blend with each other to produce a system that provides for the easy flow of traffic at the design capacity, while meeting design criteria and safety standards. • The highway should also cause a minimal disruption to historic and archeological sites and to other land-use activities. • Environmental impact studies are therefore required in most cases before a highway location is finally agreed upon. ‫نظام المحاضرات االلكتروني‬

Highway Location Process The highway location process involves four phases: •1. Office study of existing information. •2. Reconnaissance survey. •3. Preliminary location survey. •4. Final location survey.


1.Office study of existing information • The first phase in any highway location study is the examination of all available data of the area in which the road is to be constructed.

• This phase is usually carried out in the office prior to any field or photogrammetric investigation. All the available data are collected and examined. • These data can be obtained from existing engineering reports, maps, aerial photographs, and charts, which are usually available at one or more of the state’s departments of transportation, agriculture, geology, hydrology, and mining. ‫نظام المحاضرات االلكتروني‬

Data Should Be Obtained On The Following Characteristics Of The Area: • Engineering, including topography, geology, climate, and traffic volumes. • Social and demographic, including land use and zoning patterns. • Environmental, including types of wildlife; location of recreational, historic, and archeological sites; and the possible effects of air, noise, and water pollution. • Economic, including unit costs for construction and the trend of agricultural, commercial, and industrial activities.


2- Reconnaissance Survey The purpose of the reconnaissance survey is to evaluate the feasibility of one or more corridor routes for a highway between specific points that may be many kilometers away and can taking in to account the following:

1-topography,geology,climate,and traffic volume. 2-social and demographic , land use. 3-environmental. 4- economic(unit cost for construction and trends of agricultural, commercial industrial activity). ‫نظام المحاضرات االلكتروني‬

3- Preliminary Location Survey During this phase of the study, the positions of the feasible routes are set as closely as possible by establishing all the control points and determining preliminary vertical and horizontal alignments for each. Preliminary alignments are used to evaluate the economic and environmental feasibility of the alternative routes. ‫نظام المحاضرات االلكتروني‬

4- Final Location Survey

The final location survey is the detailed layout of the selected route, during which time the final horizontal and vertical alignments are determined and the final positions of structures and drainage channels are also determined.


Highway Engineering

Lecture 2

Highway Classification



•Arterial highway: a highway primarily a continuous route. •Expressway highway: a divided arterial highway for through traffic with partial or full of access and generally with grade separations at intersections. •Freeway: an expressway with full control of access. ‫نظام المحاضرات االلكتروني‬

•Full control of access: is providing y access connection with selected roads and crossing at grade separation. •Rural areas: includes urban places less than 5,000 population. •Urban areas Small urban areas

urbanized areas ‫نظام المحاضرات االلكتروني‬

Functional system for rural areas

1- rural principal arterial system 2- rural minor arterial system 3- rural collection system 4- rural local road system


Functional Highway Classification in Urban Areas

•Urban principle arterials system •Urban minor arterial system •Urban collector system •Urban local system


Cross section element • Carriageway • Shouldering • Roadway width • Right of way • Building line • Control line • Median • Camber • Side slope • Lateral and vertical • Clearance • Kerb • Guard rail

. Side drain . Other facilities


Highway Engineering

Lecture 3

The Mass Diagram



Earthwork Analysis • Average End Area Method • Consideration for shrinkage • Balance line Considerations • Limit of Freehaul (LFD) • Limit of Profitable Haul (LFH)


‫‪CUT‬‬

‫‪FILL‬‬ ‫نظام المحاضرات االلكتروني‬



Special Terms • Free haul distance (FHD)- distance earth is moved without additional compensation • Limit of Profitable Haul (LPH) - distance beyond which it is more economical to borrow or waste than to haul from the project • Overhaul – volume of material (Y) moved X Stations beyond Freehaul, measured in sta – yd3, or sta- m3 • Borrow – material purchased outside of project • Waste – excavated material not used in project ‫نظام المحاضرات االلكتروني‬

Mass Diagram Development • 1) Place FHD and LPH distances in all large loops • 2) Place other Balance lines to minimize cost of movement (theoretical) • 3) Calculate borrow, waste, and overhaul in all loops • 4) Identify stations where each of the above occur


Highway Engineering

Lecture 4



Definition of Geometric Design : • geometric design of highways deals with the dimensions and layout of visible features of the highway. • Geometric design fulfills the requirements of the driver and the vehicle, such as comfort, efficiency and safety. • Proper geometric design will help in the reduction of accidents and their severity. ‫نظام المحاضرات االلكتروني‬

Goals of geometric design • Maximize the comfort, safety and economy of facilities. • Provide efficiency in traffic operation. • Provide maximum safety at reasonable cost. • Minimize the environmental impacts. ‫نظام المحاضرات االلكتروني‬

Factors affecting geometric design : • Design speed. • Topography. • Traffic.

• Environmental factors. • Economical factors.

• Vehicles properties (dimensions, weight, operating characteristics, etc.). • Humans (the physical, mental and psychological characteristics of the driver and pedestrians like the reaction time).


Highway alignment

•First of all lets understand the meaning of the word alignment by itself. alignment : is an arrangement in a straight line or in correct relative positions. ‫نظام المحاضرات االلكتروني‬

• Highway Alignment is a three-dimensional problem • Design & Construction would be difficult in 3-D so highway alignment is split into two 2-D problems


Components of Highway Design Horizontal Alignment

Plan View Vertical Alignment Profile View ‫نظام المحاضرات االلكتروني‬

Stationing Horizontal Alignment

Vertical Alignment


Road alignment : • The position or the layout of the central line of the highway on the ground is called the alignment. • Horizontal alignment includes straight and curved paths. • Vertical alignment includes level and gradients.


Alignment decision is important because a bad alignment will enhance the construction, maintenance and vehicle operating cost. Once an alignment is fixed and constructed, it is not easy to change it due to increase in cost of adjoining land and construction of costly structures by the roadside.


Horizontal alignment : • Horizontal alignment in road design consists of straight sections of road, known as tangents, connected by circular horizontal curves.


Horizontal Alignment

Tangents ‫نظام المحاضرات االلكتروني‬

Curves

More about horizontal alignment : • It is the design of the road in the horizontal plane. • Consists of a series of tangents (straight lines), circular curves and transition curves. • Should provide safe travel at a uniform design speed.


Highway Engineering

Lecture 5



Tangents & Curves Tangent

Curve Tangent to Circular Curve


Tangent to Spiral Curve to Circular Curve

Layout of a Simple Horizontal Curve R = Radius of Circular Curve BC = Beginning of Curve (or PC = Point of Curvature) EC = End of Curve (or PT = Point of Tangency) PI = Point of Intersection T = Tangent Length (T = PI – BC = EC - PI) L = Length of Curvature (L = EC – BC) M = Middle Ordinate E = External Distance C = Chord Length Δ = Deflection Angle


Circular Curve Components


Properties of Circular Curves Degree of Curvature • Traditionally, the “steepness” of the curvature is defined by either the radius (R) or the degree of curvature (D) • Degree of curvature = angle subtended by an arc of length 100 feet R = 5730 / D (Degree of curvature is not used with metric units because D is defined in terms of feet.) ‫نظام المحاضرات االلكتروني‬

Properties of Circular Curves Length of Curve • For a given external angle (Δ), the length of curve (L) is directly related to the radius (R)

L = (RΔπ) / 180 = RΔ / 57.3 R = Radius of Circular Curve L = Length of Curvature Δ = Deflection Angle

• In other words, the longer the curve, the larger the radius of curvature ‫نظام المحاضرات االلكتروني‬

Properties of Circular Curves Other Formulas…

Tangent:

T = R tan(Δ/2)

Chord:

C = 2R sin(Δ/2)

Mid Ordinate:

M = R – R cos(Δ/2)

External Distance: E = R sec(Δ/2) - R ‫نظام المحاضرات االلكتروني‬

‫‪Circular Curve Geometry‬‬


Superelevation : • is the slope across pavement surface and is fully developed in the circular curve. (or) • Super-elevation (banking) is the transverse slope provided at horizontal curve to counteract the centrifugal force, by raising the outer edge of the pavement with respect to the inner edge, throughout the length of the horizontal curve.

• So super elevation helps the vehicle to over come the centrifugal force on the curves on pavements


• The need for super-elevation on road curves, to ensure safety against skidding and over turning with the advent of fast moving traffic. • In the past, roads were constructed without any regard to super-elevation on curves and had generally a cambered section for drainage purposes. It was little realised then that a vehicle moving on a curve had to overcome a centrifugal force to enable it to follow the curved path instead of a straight line, but, in justice to the early designers of roads, it must be said that there was no fast traffic in those days. ‫نظام المحاضرات االلكتروني‬

Side friction : • is the lateral friction, specifically its the Friction between tyre and road surface which is taken at right angles to the line of movement of the vehicle.

• Generally there are two types of friction : 1. longitudinal friction (tangential to the curve of the road). 2. lateral friction.


Highway Engineering

Lecture 6



‫‪Vertical‬‬ ‫‪Alignment‬‬


Vertical alignment : • Vertical alignment is the longitudinal section (shown on the y-axis of a road, it consists of straight grades joined by vertical curves.

• Vertical alignment specifies the elevations of points along the roadway.


Vertical Alignment • Objective: • Determine elevation to ensure • Proper drainage • Acceptable level of safety

• Primary challenge • Transition between two grades • Vertical curves G G1

2

Crest Vertical Curve ‫نظام المحاضرات االلكتروني‬

Sag Vertical Curve

G1

G2

Vertical Curve Fundamentals • Parabolic function • Constant rate of change of slope • Implies equal curve tangents

y  ax  bx  c 2

• y is the roadway elevation x stations (or feet) from the beginning of the curve


Vertical Curve Fundamentals Choose Either: • G1, G2 in decimal form, L in feet

PVC

G1

PVI

δ

G2

• G1, G2 in percent, L in stations

PVT

L/2 L x

y  ax 2  bx  c ‫نظام المحاضرات االلكتروني‬

Where: G1: Initial roadway grade( initial tangent grade) G2: Final roadway grade A: Absolute value of the difference in grades L: Length of vertical curve measured in a horizontal plane PVC: Initial point of the vertical curve PVI: Point of vertical intersection ( intersection of initial and final grades) PVT: Final point of the vertical curve

•Vertical curves are almost arranged such that half of the curve length is positioned before the PVI and half after and are referred as equal tangent vertical curves. •A circular curve is used to connect the horizontal straight stretches of road, a parabolic curve is usually used to connect gradients in the profile alignment. ‫نظام المحاضرات االلكتروني‬

• It provides a constant rate of change of slope and implies equal curve lengths.

CREST VERTICAL CURVES

+ +

Level

+

-

+ ‫نظام المحاضرات االلكتروني‬

-

‫‪SAG VERTICAL CURVES‬‬

‫‪-‬‬

‫‪-‬‬

‫‪+‬‬

‫‪-‬‬

‫‪+‬‬ ‫‪-‬‬

‫‪+‬‬

‫‪Level‬‬


Vertical Curve • For a vertical curve, the general form of the parabolic equation is; 1 Y = ax2 + bx + c where, ‘y’ is the roadway elevation of the curve at a point ‘x’ along the curve from the beginning of the vertical curve (PVC). ‘C’ is the elevation of the PVC since x=0 corresponds the PVC


dy b dx

Slope of Curve • To define ‘a’ and ‘b’, first derivative of equation 1 gives the slope.

• At PVC, x=0;

dy  2ax  b dx dy  b dx


2

or

dy G  dx

Where G1 is the initial slope.

G1  b


3

• Taking second derivative of equation1, i.e. rate of change of slope;

• The rate of change of slope can also be written as;

dy 2  2a 2 dx

4

dy 2 G2  G1  2 dx L

5


2a 

G2  G1 L

• Equating equations 4 and 5

G2  G1 2a  L

6

• or

G2  G1 a 2L ‫نظام المحاضرات االلكتروني‬

7

Fundamentals of Vertical Curves • For vertical curve design and construction, offsets which are vertical distances from initial tangent to the curve are important for vertical curve design.




PVI

PVC PVC

PVT

PVT

PVI

PVC

PVC

PVT PVI

PVC


PVT PVT

•A vertical curve also simplifies the computation of the high and low points or crest and sag vertical curves respectively, since high or low point does not occur at the curve ends PVC or PVT. •Let ‘Y’ is the offset at any distance ‘x’ from PVC. ‫نظام المحاضرات االلكتروني‬

• Ym is the mid curve offset & Yt is the offset at the end of the vertical curve. • From an equal tangent parabola, it can be written as;

A 2 y x 200 L

where ‘y’ is the offset in feet and 8‘A’ is the absolute value of the difference in grades(G2G1, in %), ‘L’ is length of vertical curve in feet and ‘x’ is distance from the PVC in feet. ‫نظام المحاضرات االلكتروني‬

Putting the value of x=L in eq. 8

A L 2 ym  ( ) 200 L 2

AL ym  800 A yf  * L2 200 L

AL yf  200 ‫نظام المحاضرات االلكتروني‬

• First derivative can be used to determine the location of the low point, the alternative to this is to use a k-value which is defined as

where ‘L’ is in feet and ‘A’ is in %.

L k A ‫نظام المحاضرات االلكتروني‬

•This value ‘k’ can be used directly to compute the high / low points for crest/ sag vertical curves by x=kG1 where ‘x’ is the distance from the PVC to the high/ low point. ‘k’ can also be defined as the horizontal distance in feet required to affect a 1% change in the slope. ‫نظام المحاضرات االلكتروني‬

Sight Distances • Sight Distance is a length of road surface which a particular driver can see with an acceptable level of clarity. Sight distance plays an important role in geometric highway design because it establishes an acceptable design speed, based on a driver's ability to visually identify and stop for a particular, unforeseen roadway hazard or pass a slower vehicle without being in conflict with opposing traffic. • As velocities on a roadway are increased, the design must be catered to allowing additional viewing distances to allow for adequate time to stop. The two types of sight distance are: • (1) stopping sight distance and (2) passing sight distance. ‫نظام المحاضرات االلكتروني‬

Stopping Sight Distance At every point on the roadway, the minimum sight distance provided should be sufficient to enable a vehicle traveling at the design speed to stop before reaching a stationary object in its path. Stopping sight distance is the aggregate of two distances: •brake reaction distance and braking distance. •Brake reaction time is the interval between the instant that the driver recognizes the existence of an object or hazard ahead and the instant that the brakes are actually applied. Extensive studies have been conducted to ascertain brake reaction time. Minimum reaction times can be as little as 1.64 seconds: 0.64 for alerted drivers plus 1 second for the unexpected signal. •Some drivers may take over 3.5 seconds to respond under similar circumstances. For approximately 90% of drivers, including older drivers, a reaction time of 2.5 see is considered adequate. This value is therefore used in Table on next page



Vehicle Stopping Distance

• Vehicle stopping distance is calculated by the following formula 2

d

where V1 f G

v1 2 g ( f  G)

initial speed of vehicle friction percent grade


Distance Traveled During Perception/ Reaction Time • It is calculated by the following formula dr = V1* tr where V1 Initial Velocity of vehicle tr time required to perceive and react to the need to stop


• Hence formula for the Stopping sight distance will be;

2

V1 SSD   V1t r 2 g ( f  G)


SSD and Crest Vertical Curve • In providing the sufficient SSD on a vertical curve, the length of curve ‘L’ is the critical concern. • Longer lengths of curve provide more SSD, all else being equal, but are most costly to construct. • Shorter curve lengths are relatively inexpensive to construct but may not provide adequate SSD. • In developing such an expression, crest and sag vertical curves are considered separately. • For the crest vertical curve case, consider the diagram.


SSD and Crest Vertical Curve S H 1

PVI PVT

PVC L


H2

S = Sight distance (ft) H1= height of driver’s eye above roadway surface (ft) L = length of the curve (ft), H2= height of roadway object (ft) , A = difference in grade Lm= Minimum length required for sight distance.

Minimum Length of the Curve • For a required sight distance S is calculated as follows; • If the sight distance is found to be less than the curve length (S>L)

• for sight distances that are greater than the curve length (S
200(

H1  A

H 2 )2

AS 2 Lm  200( H1  H 2 ) 2


• For the sight distance required to provide adequate SSD, standard define driver eye height H1 is 3.5 ft and object height H2 is 0.5 ft. S is assumed is equal to SSD. We get

SSD > L

1329 Lm  2SSD  A

SSD < L

ASSD 2 Lm  1329


•Working with the above equations can be cumbersome. •To simplify matters on crest curves computations, K- values, are used.

L = K*A where k is the horizontal distance in feet, required to affect 1 percent change in slope. ‫نظام المحاضرات االلكتروني‬


SSD and Sag Vertical Curve • Sag vertical curve design differs from crest vertical curve design in the sense that sight distance is governed by night time conditions, because in daylight, sight distance on a sag vertical curve is unrestricted. • The critical concern for sag vertical curve is the headlight sight distance which is a function of the height of the head light above the road way, H, and the inclined upward angle of the head light beam, relative to the horizontal plane of the car, β.


• The sag vertical curve sight distance problem is illustrated in the following figure.

S

H PV C

β P L VI


PV T

• By using the properties of parabola for an equal tangent curve, it can be shown that minimum length of the curve, Lm for a required sight distance is ; 200( H  S tan  ) • For S>L

Lm  2S 

• For S
A

AS 2 Lm  200( H  S tan  )


• For the sight distance required to provide adequate SSD, use a head light height of 2.0 ft and an upward angle of 1 degree. • Substituting these design standards and S = SSD in the above equations; 400  3.5SSD • For SSD>L Lm  2SSD  A

• For SSD
ASSD 2 Lm  400  3.5SSD


•As was the case for crest vertical curves, Kvalues can also be computed for sag vertical curves. •Caution should be exercised in using the kvalues in this table since the assumption of G=0 percent is used for SSD computations.



Lectures of Highway Engineering

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