Chapter Abstracts Introduction: The authors of the "Practical Guide To Railway Engineering" wish to provide the reader a general overview of the specific disciplines common to railway engineering. Railway engineering design requires that the engineer approach any modern engineering challenge with an understanding that encompasses the railway as a system; thereby requiring the practicing engineer have a general understanding of disciplines other than just their own. The text hereafter is not intended to supplant the AREMA Manual for Railway Engineering, the AREMA C&S Manual or other comprehensive texts covering specific railway engineering disciplines, but rather to provide background enabling the novice engineer or practicing engineer unfamiliar with railway engineering design to utilize available resources. Each author and contributor shares a deep love for the industry, and it is their desire that the pool of collected information be passed on to the next generation of "railroader" as well. Chapter 1 – Railway Development Chapter 1 provides a brief overview of the key occurrences in the history of transportation leading up to the introduction and implementation of railways and railway engineering in North America. The goal of this chapter is for the reader to obtain an appreciation for the reasons behind some of the key current railway engineering practices based on railway development history. The significant economic role played by innovations such as CWR, CTC, mechanization of maintenance activities, along with the evolution of bridge design, materials and construction practices is explored. Chapter 2 – Railway Industry Overview Chapter 2 is designed so the reader will gain an understand of the organizational structure of a railway and to recognize the role played in railway operations by safety, operating rules, authority of movements, speeds and traffic control systems. Critical issues affecting railway traffic systems are also considered. Various car configurations and related usage are identified along with factors governing locomotive utilization including: • horsepower and tractive effort • acceleration and balance speeds • tonnage ratings • tractive force and adhesion • ruling grade • drawbar pull • momentum grade • train resistance • power to stop • compensated grades Chapter 3 – Basic Track Chapter 3 is written for the reader to become more familiar with track components and terminology and includes over 100 illustrations. The reader will understand the criteria used to justify maintenance operations and/or capital improvement as well as recognize
the role of track geometry in maintaining and operating today's railway. Specific maintenance activities along with the function of major production gang activities are discussed. The role of safety and safety enforcement is also addressed here. Chapter 4 – Right-of-Way and Roadway Chapter 4 seeks to explain how right of way is defined and utilized. This chapter includes typical dimensions, property rights, limitations, utility easements, fencing, and vegetation. Also addressed are issues concerning; basic soil types, geotechnical behavior of various types of soils, typical track structure and the loading it imposes on the subgrade, roadbed failure (landslides and track settlement) causes and remediation, and ways to identify potential hazards to the roadbed and take appropriate action to mitigate those hazards. Chapter 5 – Drainage Chapter 5 stresses the importance of drainage in maintaining quality track. The primary hydrology and hydraulic principles are reviewed along with a demonstration of the use of commonly available resources. Consideration is provided to the impact poor drainage design can have on railway neighbors as well as the integrity of the railway itself. Chapter 6 – Railway Track Design Chapter 6 provides information pertaining to the different design elements of railway alignments, layout and design. Specific topics include horizontal and vertical alignment design, turnout geometry, location, and use; railway clearances and vehicular envelope requirements; typical yard and terminal functions and layouts. Additional considerations pertaining specifically to design elements of railway alignments and limitations are discussed as they relate to proposed use (i.e. mainline, branch line, industrial/terminal, and passenger). Chapter 7 – Communications and Signals Chapter 7 is intended as a basic overview of railway signaling. The chapter provides an appreciation of the historical development of railway signal systems as well as an understanding of basic signal terminology. An easy to understand approach explains concepts such as ABS and CTC. Basic types of signals, available energy sources, lightning and surge protection and basic track circuits including: DC track circuits, Coded DC track circuits, Style C track circuits, Overlay track circuits and AC track circuits are addressed here. An understanding of track switches, components and their interconnection to the signal system is provided. Crossing warning device theory of operation and differences between conventional and solid state devices is highlighted. The basic principles of CTC, sequence of operation and safety checks are explained along with concepts associated with microprocessor based coded track circuits and solid-state interlockings. Finally, a description of the common types of defect detectors in use is provided.
Chapter 8 – Railway Structures Chapter 8 was prepared to accomplish two primary objectives. For the novice engineer, the authors wished to provide an overview of the types of railway bridge structures and their appropriate usage as well as define the primary bridge components and their functions. Further, drainage structures, retaining walls, tunnels and sheds are classified by type as well as by common use. For the experienced highway design engineer, the common design approach differences between highway and railway bridges are reviewed. Discussion centers on the differences in design loading in Timber Chapter 7, Concrete Chapter 8 and Steel Chapter 15 of the AREMA Manual for Railway Engineering. Other critical structure criteria are highlighted such as fatigue, fracture critical members, structure serviceability, bearings and volumetric changes and composite design. Chapter 9 – Railway Electrification Chapter 9 compares the various alternatives available when considering and designing an electrified railway. A general overview of the key components and their primary function is provided for 3rd rail systems and overhead catenary systems (OCS). Fundamental criteria for selection of style of OCS are discussed along with other design basics. Finally, the impact that implementation of electrification will have on existing railroad infrastructure, staff and community is discussed. Chapter 10 – Passenger, Transit and High-Speed Rail Chapter10 presents an overview of typical design principles, construction practices and maintenance considerations applied to passenger rail lines. It describes how basic railroad engineering principles are applied in specialized ways to accommodate passenger rail requirements. The chapter notes the key distinctions between railroad and transit operations and introduces six major types of passenger rail modes. The text then discusses the service, infrastructure, regulatory (U.S.), maintenance and inspection considerations associated with each. It concludes with discussion of the special topics of line capacity and cant deficiency. Chapter 11 - Environmental Regulations And Permitting Chapter 11 is a general overview of environmental regulations and permitting in the U.S., Canada and Mexico with topics that may be encountered during railway activities (including construction, as well as operation). This information is general in nature and the reader is cautioned to contact or use a professional environmental consultant to prepare an Environmental Assessment. Information is given on wetland issues along with other topics, such as endangered species, cultural resources, Phase I environmental assessments, hazardous waste, brownfields, asbestos and air quality. Environmental information includes: the U.S. Army Corps of Engineers wetland definition, Nationwide and General permits for proposed construction activities, U.S. Army Corps of Engineers non-jurisdictional status over isolated wetlands and Best Management Practices (which
mitigate direct and indirect degradation of the environment to the extent possible). Each topic concludes on where to locate additional information. Chapter 12 – European Curve & Turnout Mechanics Chapter 12 serves to provide an appreciation of the European approach design differences in turnout and curve design from that experienced in North America. The reader will obtain an understanding of the geometrical and mathematical relationships common to both North American and European track geometry. The potential for incorporating European practices in high-speed North American transit initiatives is clearly obvious. Chapter 13 – Case Studies Chapter 13 presents four case studies drawn from actual railway design projects using formatted templates to identify critical stakeholders, identify controlling criteria, recognize potential problems, and learn from past mistakes. These case studies are intended to serve as a model for which the templates can be utilized for any railway design/construction project. It is intended that this will be part of an accessible library of case study solutions yet to be developed. Appendix The Appendix contains a wide variety of useful and related information to the material presented in the text. Included are articles describing the development of maintenance-ofway practices in the past 40 years from the perspective of a retired Class 1 chief engineer, geometry solutions for turnout and connection track location, spiral and full body curve example problem solutions, Bartlett Method of calculating throws for stringlining curves and a synopsis of one Class 1 railway’s step by step procedures for performing common maintenance and capital improvement activities. Glossary The glossary contains short definitions of the majority of the terms utilized within the text. Railway engineering terminology common to the industry is often not selfexplanatory. It is essential that the engineer have a clear understanding of the terms in use.
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Table of Contents Introduction
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Chapter 1 - Railway Development
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1.1 Introduction 1.2 Determinants of Transportation Development 1.3 Pre-Railway Transportation in North America 1.4 Physical Determinants of Land Movement 1.5 North American Railway Development and Impacts 1.6 Developments of the Twentieth Century 1.7 Development of Canadian Railways 1.8 Mexican Railway Development 1.9 Institutional Controls 1.10 History of Railway Bridge Engineering 1.11 New Technology – Bridge Developments in the Last Twenty Years 1.11.1 Existing Railway Bridges: Inspection and Assessment 1.11.2 New Railway Bridges: Materials, Design, Fabrication and Construction 1.12 Trade Journals 1.13 Other References
Chapter 2 - Railway Industry Overview
7 9 10 12 15 19 21 23 24 25 27 27 28 29 30
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2.1 Introduction 2.2 Railway Companies 2.2.1 Organization of a Railway Company Transportation Department Engineering Department Mechanical Department Marketing Department 2.3 Regulatory Agencies and Railway Associations 2.3.1 Regulatory Agencies United States Canada 2.3.2 Railroad Associations AAR and RAC AREMA REMSA RSSI 2.4 Operations of Railways 2.4.1 Safety First in Railway Operations 2.4.2 Bibles of the Railways for Safe Operations 2.4.3 Tracks and Authority of Movements 2.4.4 Speeds 2.4.5 Rail Traffic Control Systems Radio Communication of Train Orders Train Spacing and Block Separation Track Circuit Signal Block Length Centralized Traffic Control Additional Information 2-5 Railway Cars 2.5.1 Freight Cars Boxcars Insulated Boxcars and Mechanical Reefers Intermodal Cars – Piggyback Trailers and Containers Flat Cars Auto Rack Cars Gondola Cars Hopper Cars Rotary Gondola/Hopper Cars Tank Cars Maintenance-of-Way Cars Schnabel Cars 2.5.2 Hazardous Commodities 2.5.3 Passenger Cars 2.6 Locomotives 2.6.1 Horsepower (hp) and Tractive Effort 2.6.2 Tractive Force and Adhesion
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33 33 34 35 36 37 37 38 38 38 39 39 39 40 40 40 41 41 42 43 45 46 46 46 47 47 48 49 49 49 50 50 50 51 52 52 52 52 52 53 53 53 53 54 55 55
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2.6.3 Drawbar Pull 2.6.4 Train Resistance Rolling Resistance Davis Formula Starting Resistance Grade Resistance Curve Resistance 2.6.5 Compensated Grade 2.6.6 Acceleration and Balance Speed 2.6.7 Tonnage Ratings of Locomotives 2.6.8 Ruling Grade 2.6.9 Momentum Grade 2.6.10 Power to Stop 2.7 Traffic Systems 2.7.1 Priority of Trains 2.7.2 Effects Of Sharing Tracks By Freight And Passenger Trains Vs. Track Of Single Use 2.7.3 Overcoming The Delays That Occur In Freight Yards
Chapter 3 - Basic Track
56 56 56 57 57 58 58 58 59 60 60 60 61 62 63 64 65
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3.1 Track Components 3.1.1 Rail Identification of Rail 3.1.2 Ties Timber Ties Concrete Ties Steel Ties Alternative Material Ties 3.1.3 Ballast Section 3.1.4 Rail Joints Standard Joints Compromise Joints Insulated Joints 3.1.5 Tie Plates 3.1.6 Rail Anchors 3.1.7 Fasteners Spikes Bolts 3.1.8 Specialized components Derails Wheel Stops and Bumping Posts Gauge rods Sliding (Conley) Joints Mitre Rail Bridge/tunnel/overpass guard rails 3.2 Turnouts 3.2.1 Types of Turnouts Basic Turnout Terminology 3.2.2 Switch 3.2.3 Switching Mechanism 3.2.4 Turnout Rails 3.2.5 Frog Rail bound manganese (RBM) Spring Frog Solid Manganese Self-guarded Frog Bolted Rigid Frogs Movable Point Frogs Determining Frog Number 3.2.6 Switch Ties 3.2.7 Stock Rails 3.2.8 Switch Points Identifying Left or Right Hand Points 3.2.9 Specialty Components Switch Clips Switch Rods Types of Switch Rods Connecting Rod
69 69 70 72 72 75 75 76 76 78 79 79 80 82 83 83 84 85 85 86 86 87 87 87 88 88 88 89 90 91 91 92 92 93 93 94 94 94 95 95 96 97 97 97 97 98 98
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3.2.10 Special Turnout Plates Gauge Plates Switch Plates Rail Braces Heel Block Assembly Turnout Plates Hook Twin Tie Plates Frog Plates 3.2.11 Guard Rails 3.2.12 Switch Stands Spring Switch 3.3 Railway Crossings & Crossovers 3.4 Highway Crossings 3.4.1 Crossing Construction And Reconstruction 3.4.2 Crossing Warning Devices 3.5 Utility Crossings 3.6 Track Geometry 3.6.1 Gage 3.6.2 Alignment Full Body of the Curve Transition Spiral of the Curve Curve Elevation 3.6.3 Surface 3.7 Safety 3-8 Maintenance Activities 3.8.1 Track Disturbance 3.8.2 Track Disturbance Activities 3.8.3 Rail Lubrication 3.8.4 Rail Grinding 3.8.5 Rail Defect Testing 3.8.6 Geometry Cars 3.8.7 Gauge Restraint Measuring System (GRMS) 3.8.8 Vegetation Control 3.8.9 ROW Stabilization & Drainage 3.8.10 Welding 3-9 Production Gangs 3.9.1 Production Rail Gang 3.9.2 Production Tie Gang 3.9.3 Production Undercutting 3.9.4 Production Surfacing Gangs 3.9.5 Road Crossing Renewal Gangs 3.9.6 Turnout Renewal 3.9.7 New Track Construction/Cutout Track Construction /Cutovers References:
99 99 100 100 101 101 101 102 102 103 103 104 106 108 110 111 112 114 115 116 117 117 118 120 122 124 125 126 127 128 128 129 129 131 132 133 134 136 138 139 142 143 New 144 147
Chapter 4 - Right-of-Way & Roadway
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4.1 Introduction 4.2 Right-of-Way 4.2.1 Right-of-Way Width 4.2.2 Fences 4.2.3 Utilities 4.2.4 Vegetation 4.3 Roadway 4.3.1 Soils Definition Soil Types Major Soil Divisions Soil Texture and Composition 4.3.2 Geotechnical Processes The Concept of Stress and Strain Effective Stress The Effect of Porewater Pressure Clays Sand and Gravel Silt Soil Behavior Under Rapid Loading Effect of Shear Strain Settlement Seepage
151 152 152 153 154 154 155 155 155 157 157 160 161 161 162 162 163 163 164 164 164 165 166
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4.3.3 Track Structure Historical Background Components and Functions Subgrade Sub-ballast How Track Fails 4.3.4 Instability Main Features of Landslides Slides that Affect the Track Triggering Mechanisms Remediation Soil Improvement Improved Slope Geometry Reduce Seepage Pressure Structural Support Inspection of Slopes Monitoring Slope Movements Areas With the Greatest Hazard 4.3.5 Settlement Basic Theory Influence of Construction Methods Influence of Soil Type 4.3.6 Hazard Identification Understanding the Factors Understanding the Mechanisms Identifying the Hazard 4.3.7 Summary
167 167 168 169 170 170 172 172 172 174 175 176 176 178 179 180 180 181 182 182 183 183 184 184 185 185 185
Chapter 5 – Drainage
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5.1 Hydrology 5.1.1 Equations and Programs 5.1.2 Rainfall Intensity or Precipitation 5.1.2 Rainfall Intensity or Precipitation 5.1.3 Time of Concentration 5.1.4 Distribution 5.2 Hydraulics 5.2.1 Open Channel Hydraulics 5.2.2 Culvert Hydraulics 5.3 Recommended Procedures 5.3.1 Existing Drainage Study 5.3.2 Proposed Drainage System 5.3.3 Floodplain Encroachment Evaluation 5.3.4 Erosion Control Evaluation
191 192 194 195 197 198 198 198 202 210 210 211 212 213
Chapter 6 - Railway Track Design
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6.1 Stationing 6.2 Horizontal Alignments Staking Spirals By Deflections Staking Spirals By Offsets Applying The Spiral To Compound Curves (Arema 1965) 6.3 Vertical Alignments 6.4 Alignment Design 6.5 Turnouts 6.6 Design Of Yards 6.7 Clearances References:
218 219 227 228 228 229 232 244 253 256 262
Chapter 7 - Communications & Signal
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7.1 Introduction to Signals 7.1.1 Railway Operation 7.1.2 Timetable Operation 7.1.3 Wayside Signals 7.1.4 Color Light Signal 7.1.5 Signal Terminology 7.1.6 Searchlight Signal 7.1.7 Operating Principle 7.1.8 Automatic Block Signals 7.1.9 Signal Location 7.1.10 Common Terms 7.1.11 Automatic Block Signal System
265 265 266 268 269 269 270 270 271 272 273 274
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7.1.12 Centralized Traffic Control (CTC) 7.2 Energy Source 7.2.1 Batteries 7.2.2 Battery Charging 7.2.3 Lightning Protection 7.3 Track Circuits 7.3.1 DC Track Circuits 7.3.2 Track Circuit Operation 7.3.3 Train Shunting 7.3.4 Coded DC Track Circuit 7.3.5 Style “C” Track Circuit 7.3.6 Overlay Track Circuits 7.3.7 Overlay Track Circuit Operation 7.3.8 Track Coupling Unit 7.3.9 AC Track Circuits and Relays 7.3.10 Apparatus Used with AC Track Circuits 7.4 Track Switches 7.4.1 Hand Operated Switch with SCC 7.4.2 Electric Switch Lock 7.4.3 Dual Controlled Power Switch Machine 7.5 Highway Crossings 7.5.1 Crossing Operation 7.5.2 Crossing Gates 7.5.3 Crossing Motion Detector/Predictor 7.6 Centralized Traffic Control (CTC) 7.6.1 Operation 7.6.2 Sequence of Operation 7.6.3 Microprocessor Based Coded Track Circuits 7.6.4 Theory of Coded Track Circuit Operation 7.6.5 Solid State Interlocking 7.7 Defect Detectors 7.7.1 Hot Box Detector 7.7.2 Hot Wheel Detector 7.7.3 Dragging Equipment Detector 7.7.4 Wheel Defect Detector 7.7.5 Slide Fence 7.7.6 Flood Detectors 7.7.7 Fire Detectors 7.7.8 High/Wide Load Detectors
275 275 275 276 278 279 279 280 282 283 286 287 288 288 289 290 291 291 293 294 297 298 299 300 302 302 305 308 309 311 313 313 313 313 314 315 316 316 316
Chapter 8 - Railway Structures
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8.1 Introduction to Railway Structures 8.2 Major Bridge Components 8.2.1 Substructure Investigate Underlying Soil & Geologic Conditions Piling Abutments and Piers 8.2.2 Superstructure 8.2.3 Bridge Deck Open Bridge Decks Ballasted Decks Open Deck Vs. Ballast Deck 8.3 Bridge Types 8.3.1 Timber Trestles Terminology Caps Stringers Timber Connectors 8.3.2 Steel Bridges Girder Spans Truss Spans Steel Trestles Viaducts 8.3.3 Concrete Bridges Arches Rigid-Frame Bridge Slab Bridges Concrete Trestles Concrete Girders
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320 321 322 322 322 327 329 330 331 333 335 337 337 337 339 339 340 340 340 342 345 345 346 346 346 347 347 348
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8.3.4 Moveable Spans Bascule Bridges Swing Span Bridges Vertical Lift Bridges 8.4 Other Structures 8.4.1 Drainage Structures 8.4.2 Retaining Walls Gravity Retaining Walls Crib Walls Sheet Piling Mechanically Stabilized Earth Drainage of Retaining Walls 8.4.3 Tunnels Tunnel Construction Methods 8.4.4 Sheds 8.5 Structural Design Considerations 8.5.1 Introduction 8.5.2 Bridge Loading, Dead Load Live Loads Impact Centrifugal Load Lateral Loads Longitudinal Loading Wind Loading Stream Flow, Ice and Buoyancy Seismic Loads Combined Loads 8.5.3 Other Structure Design Criteria Fatigue Fracture Critical Members (FCM) Structure Serviceability Bearings and Volumetric Changes Composite Design Bridge Design Assumptions and Constructibility Issues Recommended Construction Considerations 8.5.4 Retaining Wall Loads References:
Chapter 9 - Railway Electrification
349 349 351 352 355 355 356 356 356 358 359 360 361 361 364 365 365 366 366 367 370 372 374 375 377 378 379 381 381 381 382 383 385 387 388 389 391 392
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9.1 Introduction 9.2 Development of Motive Power for Railways 9.2.1 Pioneers of Electric Traction Development 9.3 Rail Operation Classification 9.4 Mainline Railways and Independent Short Lines 9.4.1 Mainline Electrification Studies 9.4.2 Mainline Infrastructure Compatibility Maintenance Staff Safety 9.4.3 Impacts of Mainline Railway Electrification on Communities. 9.5 Urban Railways 9.5.1 Impacts of an Urban Electrified Light Rail or Commuter Rail System on the Community 9.6 Existing Electrification Systems 9.7 New Electrification Systems 9.7.1 Sources of Primary Power 9.7.2 Substations 9.7.3 Power Distribution Systems Feeder Cable Sub Systems Negative Feeder Cable Sub Systems Contact System Sub Systems 9.7.4 Current Collectors Contact Shoe Trolley Poles Pantographs 9.7.5 Characteristics Of Third Rail System Conductor Rail Supports 9.7.6 Characteristics Of An Overhead Contact System Single Wire System Catenary Systems
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395 395 398 401 403 404 406 408 408 409 409 410 411 414 415 415 417 417 418 418 419 419 420 420 421 421 422 423 425
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9.7.7 OCS Style Selection Location and Environment Copper Cross-sectional Area Economics Cost Factors of OCS Styles OCS Design Basics 9.8 Electrification Interfaces with Other Rail Elements 9.8.1 Right-of-Way Track Layout/Realignment Substations Supporting Structures for the Contact System Systemwide Ductbanks 9.8.2 Track Structure 9.8.3 Civil Structures Tunnels To Be Electrified Bridges Over Electrified Track Bridges Under Electrified Track Station Canopies OCS Attachments 9.8.4 Signals and Communications 9.9 Interfaces with Project-Wide Staff Bibliography
428 429 429 430 433 433 434 434 434 435 435 435 435 436 436 437 437 437 437 438 439 443
Chapter 10 - Passenger, Transit & High Speed Rail
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10.1 Introduction 10.2 Passenger Rail Modes 10.3 Distinctions between Railway Operations and Transit Operations 10.4 Passenger Rail Service and Vehicle Characteristics by Mode 10.5 Passenger Rail Infrastructure Characteristics by Mode 10.6 Passenger Railway Infrastructure Characteristics 10.6.1 High-Speed Rail (HSR) Route Alignment Considerations Regulatory Compliance 10.6.2 Intercity Rail and Commuter Rail General Route Alignment Considerations Track Standards Regulatory Compliance 10.7 Transit Infrastructure Characteristics 10.7.1 Rapid Transit Route Alignment Considerations Track Standards Regulatory Compliance 10.7.2 Light Rail Transit (LRT) Route Alignment Considerations Track Standards Regulatory Compliance 10.7.3 Streetcar and Vintage Trolley Route Alignment Considerations Track Standards Regulatory Compliance 10.8 Passenger Railway Maintenance Considerations Maintenance Philosophy Maintenance Practices 10.9 Transit Maintenance Considerations Maintenance Philosophy Maintenance Practices 10.10 Special Topics Associated with Passenger Railway Operations 10.10.1 Passenger Railway Line Capacity 10.10.2 The Impact of Superelevation (Or Cant Deficiency and Why It’s Important) 10.11 Conclusion
Chapter 11 - Environmental Conditions & Permitting 11.1 Introduction 11.2 Environmental Regulations Of The United States 11.2.1 Wetlands Regulations U.S. Army Corps of Engineers Regulatory Boundaries 11.2.2 Wetland Definition
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447 448 449 450 451 453 453 453 454 455 455 455 455 456 457 457 457 457 459 459 459 459 461 461 461 461 461 462 462 462 463 463 464 465 465 467 469
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11.2.3 Wetland Regulations Nationwide Permits General Permits USACE Non-Jurisdiction Over Isolated Wetlands 11.2.4 Best Management Practices 11.2.5 Endangered Species 11.2.6 Cultural Resources 11.2.7 Phase I Environmental Assessment 11.2.8 Hazardous Waste 11.2.9 Brownfields 11.2.10 Asbestos 11.2.11 Air Quality 11.3 Environmental Regulations Of Canada 11.3.1 Canadian Wetlands Environmental Assessment Guidelines 11.3.2 Endangered Species 11.3.3 Hazardous Waste 11.3.4 Air Quality 11.4 Environmental Regulations Of Mexico 11.4.1 Regulations 11.4.2 Mexico Regulation for Hazardous Waste 11.5 Wetland Case Study
Chapter 12 - European Curve and Turnout Mechanics 12.1 Introduction 12.2 Curves 12.2.1 Curve Definition 12.2.2 Gage 12.2.3 Elevation in Curves 12.2.4 Elevation Transition 12.2.5 Track Warp 12.2.6 Horizontal Transition Curves 12.2.7 Theory of the Transitional Curves 12.3 Gradient Change 12.4 Turnouts and Turnout Design 12.4.1 Measuring the Frog Angle 12.4.2 Turnout Calculations 12.4.3 Clothoidal Turnout 12.5 Speed Raising Improvements 12.5.1 Curve Improvements 12.5.2 Surfacing and Lining
481 481 486 487 488 488 491 492 494 496 496 497 499 500 502 503 504 504 505 506 507
511 513 514 514 515 517 518 523 524 526 529 531 533 534 537 540 542 543
Chapter 13 - Case Studies
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13.1 Introduction #1 – Kasky, KY – Project Survey #2 – Crestline, OH – Project Survey #3 – FEC/SFRC Connection, West Palm Beach, FL For Amtrak Service – Project Survey #4 - Ft. Washington PA – Project Survey
Appendix
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Applied Science For Railway Tracks Turnouts, Connections, And Crossings Turnouts Location of Turnouts Turnouts from Straight Track Turnouts from Curved Track Connections From Straight Track Turnout from the Inside of a Curved Main Track Turnout from the Outside of a Curved Main - Track Parallel Tracks - Sidings Parallel Tracks Both Straight Tracks Parallel Tracks - Curved Tracks Parallel Tracks - Crossovers Crossovers - Straight Tracks. Crossovers - Curved Tracks Ladder Tracks Intersecting Tracks Intersecting Tracks - Both Tracks Straight Intersecting Tracks - One Straight and One Curved Track Intersecting Tracks - Both Tracks Curved
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A-3 B-1 B-1 B-1 B-2 B-3 B-3 B-3 B-5 B-12 B-17 B-17 B-18 B-22 B-23 B-24 B-25 B-27 B-27 B-31 B-34
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Wye Tracks Wye Track - Straight Main Track Wye Track - Curved Main Track Diamond Turnouts Crossings Crossing Data Straight Crossings Single-Curve Crossings Double-Curve Crossings Example Curve Problems With Solutions PROBLEM 1. PROBLEM 2. PROBLEM 3. PROBLEM 4. PROBLEM 5. PROBLEM 6. PROBLEM 7. PROBLEM 8. PROBLEM 9. PROBLEM 10. PROBLEM 11. Spiral Problems & Solutions Determining Degree Of Curvature Method Of Determining Degree Of Curvatue String Lining Curves Stringlining Of Railroad Curves Maintenance Processes Ballast Unloading Gauging on Wood and Concrete Ties Mechanical Surfacing of Track Switch Tie, Yard and Siding Ties & Programmed Maintenance Tie Renewal Rail Train Rail Pickup CWR Rail Relay on Wood or Concrete Ties Mechanized Tie Renewal Track Abandonment Track Sledding Installation of Panelized Turnouts Unloading Continuous Welded Rail (CWR) GLOSSARY
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B-35 B-36 B-37 B-38 B-39 B-40 B-41 B-42 B-43 C-1 C-1 C-1 C-1 C-2 C-2 C-3 C-4 C-8 C-9 C-13 C-18 D-1 E-1 E-2 F-1 G-1 H-1 H-3 H-7 H-11 H-17 H-22 H-27 H-32 H-37 H-44 H-50 H-57 Glossary-1
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Railway Development 1.1 Introduction History “Ring Out, oh bells. Let cannons roar In loudest tones of thunder The iron bars from shore to shore Are laid and Nations wonder”
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his quote from the May 11, 1869 The Chicago Tribune celebrated the completion in Utah of the first transcontinental railway connection in North America. By 1885 the Canadian Pacific completed the first single company transcontinental line and the Atlantic and Pacific were also first linked in Mexico in the 19th century. The exciting impact of a technology that reduced a six-month to a six-day trip can hardly be imagined today. In the lifetime of anyone reading this, we have seen nothing with the impact on all aspects of life as the development of the railway. Only 44 years earlier on October 27, 1825 George Stephenson’s steam locomotive, “Locomotion Number 1” hauled a 90 ton load consisting of 36 cars carrying more than 500 passengers and some freight at a sustained speed of 12 mph along the Stockton and Darlington Railway in northern England. This was the culmination of decades of imagination, promotion, engineering and experimentation. What is a railway? A railway can be defined as an engineered structure consisting of two metal guiding rails on which cars are self-propelled or pulled by a locomotive. In his book John Armstrong defines a railway as: “A railroad consists of two steel rails which are held a fixed distance apart on a roadbed. Vehicles, guided and supported by flanged steel wheels and connected into trains, are propelled as a means of transportation.” Webster’s Dictionary (1986) defines a railroad as “1. A road laid with parallel steel rails, along which cars carrying
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passengers or freight are drawn by locomotives, 2. A complete system of such roads, including land, rolling stock, stations, etc. 3. The persons or corporation owning and managing such a system.” The terms railway and railroad are sometimes used interchangeably. However, for this book, railway will generally refer to the track and other closely associated items, i.e., signals, crossings, bridges, etc. Railroad will be used where the usage connotes the bigger system. In commencing a railway engineering career, you are joining many fellow workers in a complex and increasingly coordinated activity that is an integral part of any civilized society. About one-seventh of the workers in advanced economies are involved in some phase of transportation. Transportation, the movement of persons and goods, of which railroading is a large and vital part, is tied in with the location and magnitude of all kinds of human activity which depend on the timely availability of quality goods and services. This ranges from the necessities of food and fuel and work to leisure pursuits. Many of you will be considered as transportation engineers specializing in railway engineering (not operating trains). We can define railway engineering as that branch of civil engineering involved in the planning, design, construction, operation and maintenance of railway land facilities used for the movement of people and goods serving the social and economic needs of contemporary society and its successors. The complete railway engineer is active in all aspects of civil engineering practice, surveying, geotechnics, hydrology, hydraulics, environmental and sanitary and structural design as well as construction technology. You will frequently encounter the word “mode” in your railway practice. A mode of transportation is no more than a particular type of transportation defined in enough detail for the purpose at hand. It can be as general as the medium through or on which transportation takes place; for example, air, sea and land modes. The walking or pedestrian mode involves the moving human. The public transportation mode includes those systems such as rail commuter lines and public bus and taxi service. Often, far more detailed descriptions are needed for effective analysis, communication and understanding. The railway mode is a type of a land transportation mode as defined above. The light rail transit mode is a further more specifically defined type of rail service, typically today an urban, electrically powered system operating on its own right of way with intersections with intersecting public streets. Other terms used in railway engineering are listed and defined in the Glossary found at the end of this Manual.
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Flange Out
Grooved
Haunch
Ringwalt
Figure 1-5 English Railways and Freight Cars, as Illustrated in Strickland’s Report, 1826
Railways quickly became a major factor in accelerating the great westward expansion, as well as tying the older eastern population and industrial centers together, by providing a reliable, economic and rapid means of transportation. As additional lines were built, they facilitated the establishment and growth of towns in the West. Except for the trip from farm to railhead in town, the poor roads and limited canals became irrelevant. The Federal government and states encouraged and provided financial support through land grants and loans, which were paid back with reduced rates for half a century. Since the first railways, there have been many improvements in all aspects of railroading. For example, the development of the iron flanged “T” rail was achieved by 1840. (See Figure 1-8 for an early track section) Until mass steel making was developed, there was a continuing controversy between the use of malleable iron vs. cast iron for rail. By 1840 wooden ties kept in place by ballast stone had replaced simple stone surface support.
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he railway industry encompasses not only the operating railway companies and transit authorities, but also the various government regulatory agencies, railway associations, professional organizations, manufacturers and suppliers of locomotives, railcars, maintenance work equipment and track materials, consultants, contractors, educational institutes and, most important of all, the shipping customers. The information in this chapter is of a general nature and may be considered as typical of the industry. However, each railway company is unique and as such it must be understood what is included in this chapter may not be correct for a particular company.
2.2 Railway Companies Government owned freight railways are nowadays limited to some regional lines where transportation service must be protected for the economic well being of the communities. Passenger railways, on the other hand, are generally owned by governments. Transcontinental services, such as the Amtrak or VIA Rail in Canada, are corporations solely owned by the respective Federal Governments. These passenger railway companies normally do not own the trackage infrastructures. Except for certain connecting routes and dedicated high-speed corridors, they merely operate the passenger equipment on existing tracks owned by freight railways. Local rapid transit systems are usually operated as public utilities by the individual municipalities or transit authorities on their own trackage. Commuter services may be operated by government agencies or private sector on either their own or other railway owned trackage.
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The tractive effort (in pounds) available from a locomotive can be roughly calculated as: Tractive Effort (lbs.) = Horsepower X (308) Speed (mph) Where 308 is 82% of 375 lb-miles per hour per hp. For example, a 3000 hp locomotive will have approximately 74,000 lbs. tractive effort at 12.5 mph.
2.6.2 Tractive Force and Adhesion It is the tractive force at the locomotive driving wheels (drivers) at the rail that starts and moves tonnage up various grades. The maximum tractive force that can be developed at the rail is equal to the weight on drivers multiplied by the adhesion (coefficient of friction) of the wheels on the rail. The primary factors, among others, affecting adhesion are rail condition and speed. Adhesion decreases as speed increases. At about 10 mph, adhesion varies from less than 10% on slimy, wet rail to about 40% on dry, sanded rail. In general, with the aid of the sanders, approximately 25% adhesion is usually available. As all the wheels on most diesel locomotives are driving wheels, the weight of the locomotives must be about four times the tractive force developed. The HHP (high horsepower) units for main line service weigh about 195 tons each on 6 axles. The maximum tractive force is therefore approximately 97,000 lb. per locomotive or 16,000 lb. per axle; that is, if there is enough horsepower at the wheel rims to develop the tractive effort.
2.6.3 Drawbar Pull After some of the tractive effort is used to move the locomotive itself, the remaining effort, in the form of “drawbar pull,” is used to move the rest of the train. As the train speed increases, the tractive effort from the locomotives decreases and the drawbar pull available to move the train also decreases. Due to the limited strength of drawbars and coupler knuckles, the number of locomotives or motorized axles that can be used in the head end of a train is restricted. Although rated with a minimum strength of 350,000 lb. (general service coupler made of Grade B steel), coupler knuckle failure may happen at 250,000 lb. due to age and wear. Grade E knuckles used on some captive services may have an ultimate strength of 650,000 lb. To avoid the risk of drawbar failure enroute, it is recommended to limit the number of motorized axles in a locomotive consist to 18 (three 6-axle units). If more tractive
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effort is required to move the tonnage of a train, the option of in-train motive power should be considered.
2.6.4 Train Resistance Train resistance, the force required to move a train, is the sum of the rolling resistance on tangent level track, grade resistance and curve resistance of the locomotives and cars. Other resistances due to wind velocity, tunnels or different train marshalling will not be discussed here. Rolling Resistance Rolling Resistance is the sum of the forces that must be overcome by the tractive effort of the locomotive to move a railway vehicle on level tangent track in still air at a constant speed. These resistive forces include: §
Rolling friction between wheels and rail that depends mainly on the quality of track.
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Bearing resistance, which varies with the weight on each axle and, at low speed, the type, design and lubrication of the bearing.
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Train dynamic forces that include the effects of friction and impact between the wheel flanges against the gauge side of the rail and those due to sway, concussion, buff and slack-action. The rail-flange forces vary with speed and quality of the wheel tread and rail, as well as the tracking effect of the trucks.
§
Air resistance that varies directly with the cross-sectional area, length and shape of the vehicle and the square of its speed.
In general, rolling resistance of a train, R (in lb.), can be calculated using an empirical expression as follows: R = A + B V + C D V2 where A, B, C & D are coefficients defining the different resistive forces that are either independent, dependent or affected by the square of the train speed V. Davis Formula The first empirical formula to compute rolling resistance was developed by W.L. Davis in 1926. The original Davis formula provided satisfactory results for older equipment with journal bearings within the speed range between 5 and 40 mph. Roller bearings, increased dimensions, heavier loadings, higher train speeds and changes to track structure have made it necessary to modify the coefficients proposed by Davis. Since
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then, there had been various modifications. Interested readers may refer to Section 2.1 of Chapter 16 in the AREMA Manual for Railway Engineering for more information. Starting Resistance The resistance caused by friction within a railway vehicle’s wheel bearings can be significantly higher at starting than when the vehicle is moving. Depending on the type of bearings, weight per axle, and the temperature of the bearing, starting resistance can range from 5 to 50 lb/ton. The ambient temperature and the duration of the stop as shown below affect temperature of the bearing. Type of Bearings
Above Freezing
Below Freezing
Journal Bearing
25 lb/ton
35 lb/ton
Roller Bearing
5 lb/ton
15 lb/ton
Starting resistance is generally not much of a problem with the very large tractive effort available with modern diesel locomotives, except on steeper grades. If necessary, the locomotive engineer can bunch up the train first, then start the train one car at a time. The cars already moving will help start the ones to the rear. This is called “taking slack” to start. Grade Resistance Grade Resistance is the force required to overcome gradient and is equal to 20 lb. per ton per percent grade. This force is derived from the resolution of force vectors and is independent of train speed. An up grade produces a resistive force while a down grade produces an accelerating (negative resistive) force. A train moving up a long tangent of 1% grade at 10 mph, a speed that most tonnage trains slow down to at ruling grade locations, will have a train resistance coefficient of 22.4 to 23.5 lb. per ton with the grade resistance accounted for over 85% of the total. Curve Resistance Curve Resistance is an estimate of the added resistance a locomotive or car must overcome when operating through a horizontal curve. The exact details of the mechanics contributing to curve resistance are not easy to define. It is generally accepted in the railway industry that curve resistance is approximately the same as a 0.04% up grade per degree of curvature (which equals 0.8 lb. per ton per degree of curvature) for standard gauge tracks. At very slow speeds, say 1 or 2 mph, the curve resistance is closer to 1.0 lb. (or 0.05% up grade) per ton per degree of curve.
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Basic Track The engineer will frequently work from a set of standardized railway or transit standards when making his or her selection of track components for any given design project. However, a basic understanding of elementary track componentry, geometry and maintenance operations is necessary if intelligent decisions are to be made within the options that are typically available.
3.1 Track Components
W
e begin our study with the prime component of the track – the rail.
3.1.1 Rail Rail is the most expensive material in the track.2 Rail is steel that has been rolled into an inverted "T" shape. The purpose of the rail is to:
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Transfer a train's weight to cross ties.
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Provide a smooth running surface.
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Guide wheel flanges.
Canadian National Railway Track Maintainer’s Course
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Switch Ties Switch ties (Figure 3-3) are commonly hardwood species, usually provided in either 6" or 12" increments beginning at 9'-0" up to 23'-0" in length. Nominal cross-section dimensions are 7" x 9", although larger ties are specified by some railways. The primary use for switch ties is relegated to turnouts (thus their name). However, they are also used in bridge approaches, crossovers, at hot box detectors and as transition ties. Some railways use switch ties in heavily traveled Figure 3-3 Switch Timber – Photo by Craig Kerner road crossings and at insulated rail joints. Switch ties ranging in length from 9'-0" to 12'-0" can also be used as "swamp" ties. The extra length provides additional support for the track in swampy or poor-drained areas. Some railways have utilized Azobe switch ties (an extremely dense African wood) for high-speed turnouts. The benefits associated with reduced plate cutting and fastener retention may be offset by the high import costs of this timber. Softwood Ties Softwood timber (Figure 3-4) is more rot resistant than hardwoods, but does not offer the resistance of a hardwood tie to tie plate cutting, gauge spreading and spike hole enlargement (spike killing). Softwood ties also are not as effective in transmitting the loads to the ballast section as the hardwood tie. Softwood and hardwood ties must not be mixed on the main track except when changing from one category to another. Softwood ties are typically used in open deck bridges.
Figure 3-4 Softwood Timber - Photo by J. E. Riley
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Concrete Ties Concrete ties (Figure 3-5) are rapidly gaining acceptance for heavy haul mainline use, (both track and turnouts), as well as for curvature greater than 2°. They can be supplied as crossties (i.e. track ties) or as switch ties. They are made of pre-stressed concrete containing reinforcing steel wires. The concrete crosstie weighs about 600 lbs. vs. the 200 lb. timber track tie. The concrete tie utilizes a Figure 3-5 Concrete Ties – Photo by Kevin Keefe specialized pad between the base of the rail and the plate to cushion and absorb the load, as well as to better fasten the rail to the tie. Failure to use this pad will cause the impact load to be transmitted directly to the ballast section, which may cause rail and track surface defects to develop quickly. An insulator is installed between the edge of the rail base and the shoulder of the plate to isolate the tie (electrically). An insulator clip is also placed between the contact point of the elastic fastener used to secure the rail to the tie and the contact point on the base of the rail. Steel Ties Steel ties (Figure 3-6) are often relegated to specialized plant locations or areas not favorable to the use of either timber or concrete, such as tunnels with limited headway clearance. They have also been utilized in heavy curvature prone to gage widening. However, they have not gained wide acceptance due to problems associated with shunting of Figure 3-6 Steel Ties signal current flow to ground. Some lighter models have also experienced problems with fatigue cracking.
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3.1.4 Rail Joints The purposes of the rail joint (made up of two joint bars or more commonly called angle bars) are to hold the two ends of the rail in place and act as a bridge or girder between the rail ends.6 The joint bars prevent lateral or vertical movement of the rail ends and permit the longitudinal movement of the rails for expanding or contracting. The joint is considered to be the weakest part of the track structure and should be eliminated wherever possible. Joint bars are matched to the appropriate rail section. Each rail section has a designated drilling pattern (spacing of holes from the end of the rail as well as dimension above the base) that must be matched by the joint bars. Although many sections utilize the same hole spacing and are even close with regard to web height, it is essential that the right bars are used so that fishing angles and radii are matched. Failure to do so will result in an inadequately supported joint and will promote rail defects such as head and web separations and bolt hole breaks. There are three basic types of rail joints (Figure 3-8): •
Standard
•
Compromise
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Insulated
Figure 3-8 Conventional Bar, Compromise Bar & Insulated Joint Bar – Photo by J. E. Riley
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Standard Joints Standard joint bars connect two rails of the same weight and section. (See Figure 3-9) They are typically 24" in length with 4-bolt holes for the smaller rail sections or 36" in length with 6-bolt holes for the larger rail sections. Alternate holes are elliptical in punching to accommodate the oval necked track bolt. Temporary joints in CWR require the use of the 36” bars in order to permit drilling of only the two outside holes and to comply with the FRA Track Safety Standard’s requirement of maintaining a minimum of two bolts in each end of any joint in CWR.
Figure 3-9 Standard Head-Free Joint Bar – Photo by J. E. Riley
Compromise Joints Compromise bars connect two rails of different weights or sections together. (See Figure 3-10) They are constructed such that the bars align the running surface and gage sides of different rails sections. There are two kinds of compromise joints: •
•
Directional (Right or Left hand) compromise bars are used where a difference in the width of the head between two sections requires the offsetting of the rail to align the gage side of the rail.
Figure 3-10 Compromise Joint Bar – Photo by J. E. Riley
Non-directional (Gage or Field Side) are used where the difference between sections is only in the heights of the head or where the difference in width of rail head is not more than 1/8" at the gage point. Gauge point is the spot on the gauge side of the rail exactly 5/8" below the top of the rail.
To determine a left or right hand compromise joint: •
Stand between the rails at the taller rail section.
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Face the lower rail section.
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The joint on your right is a "right hand".
•
The joint on your left is a "left hand".
Insulated Joints Insulated joints are used in tracks having track circuits. They prevent the electrical current from flowing between the ends of two adjoining rails, thereby creating a track circuit section. Insulated joints use an insulated end post between rail ends to prevent the rail ends from shorting out. There are three types of insulated joints: •
Continuous
•
Non-continuous
•
Bonded
Continuous insulated joints (Figure 311) are called continuous because they continuously support the rail base. No metal contact exists between the joint bars and the rails. Insulated fiber bushings and washer plates are used to isolate the bolts from the bars. The joint bars are shaped to fit over the base of the rail. This type of insulated joint requires a special tie plate called an "abrasion plates" to properly support the joint.
Figure 3-11 Continuous Insulated Joint – Photo by J. E. Riley
Non-continuous insulated rail joints are called non-continuous because these joints don't continuously support the rail base. A special insulating tie plate is required on the center tie of a supported, non-continuous insulated joint. Metal washer plates are placed on the outside of the joint bar to prevent the bolts from damaging the bar. There are two common kinds of non-continuous insulated joints: •
Glass fiber.
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Polyurethane encapsulated bar.
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Right-of-Way & Roadway For this chapter, think of the railway right-of-way as the area from fence to fence without the track and structures. The roadway is considered to be any construction within the right-of-way except the track, bridge structures, signals and crossings.
4.1 Introduction
T
he railway right-of-way (often referred to as the roadway) includes the subgrade upon which the ballast section and track are built, along with adjacent improvements and features required to support and maintain the railway track. The right-of-way is often thought of as the strip of land on which the railway and its supporting features are built. The right-of-way typically includes ditches running along the track and related drainage structures required to divert water past and away from the railway. The issue of drainage is covered in Chapter 5. It also includes any embankments and cuts on which, or through which, the railway is built, their side slopes and the vegetation covering the slopes. It may also include any retaining walls or other earth-supporting structures required to hold railway embankment and cut side slopes in place. It includes fences, signs, utilities and outlying structures. The bulk of this chapter deals with what the railways are built upon, the soil. Just as concrete and steel are the materials used by the structural engineer, soil is the main building material for the railway. In the same way as there are various types of steel, or diverse mixtures of concrete, there are many classifications of soil. Some soils are suitable for use as ballast and sub-ballast (sand and gravel), some as subgrade materials (sand, gravel, clay, etc.), while others are totally undesirable for any use in railway construction (e.g., organic soils). A major difference between soils and most other construction materials is that soil is a natural material and is subjected to little or no processing before use. It is therefore essential to identify the various soils and avoid using those that may give problems, since it is seldom that soil can be processed to improve its properties. From a
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construction and maintenance over the past 100 years. For instance, it is not unusual for track that functioned very well for more than 50 years to suddenly develop severe geotechnical problems. In solving problems today, the experiences and effects of the last 100 to 150 years of railway practice must be considered. Not only are the railways dealing with everincreasing loads and ever-increasing traffic, but also a maintenance effort focused on rails and ties. Ballast, being less visible, receives less attention, and the subgrade, less still except when problems develop. Nonetheless, knowing the history of a section of track is an important component of effective track maintenance. Components and Functions
SUBBALLAST SUBGRADE Figure 4-4 The Track Structure
The track structure is made up of subgrade, sub-ballast, ballast, ties and rail as illustrated in Figure 4-4. Each of these contributes to the primary function of the track structure, which is to conduct the applied loads from train traffic across the subgrade safely. The magnitudes of typical stresses under a 50,000 lb axle load are shown in Figure 4-5. These stresses are applied repeatedly, and each repetition causes a small amount of deformation in the subgrade. In theory, the track structure should be designed and constructed to limit rail deflections to values which do not produce excessive rail wear or rates of rail failure. In reality, cumulative deformation of the subgrade causes distortion of the subgrade, leading to formation of “ballast pockets" (Figure 4-6) or outright shear failure.
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Figure 4-5 Stresses Imposed by Train Axle Load
Figure 4-6 Ballast Pockets in Subgrade
Subgrade The purpose of the subgrade is to support the track structure with limiting deflections. Every subgrade will undergo some deflection (strain) as loads (stress) are applied. The total displacement experienced by the subgrade will be transmitted to other components in the track structure. The stiffer the subgrade (i.e., the higher the modulus of elasticity), the lower the deflection values will be. It is important that adequate subgrade strength and stiffness be available on a year-round basis, particularly during spring thaw and following heavy precipitation events. The strength, stiffness and total deflection of the subgrade can be improved by:
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Carefully selecting materials that are naturally strong (sand, gravel, boulders) with a high angle of internal friction.
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Limiting access to water to avoid buildup of porewater pressure and subsequent reduction of strength.
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Improving the soil properties, using techniques such as compaction, in situ densification, grouting and preloading.
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Maintain good drainage.
§
Maintain stable subgrade geometry.
Sub-ballast The purpose of sub-ballast is to form a transition zone between the ballast and subgrade to avoid migration of soil into the ballast, and to reduce the stresses applied to the subgrade. In theory, the gradation of the sub-ballast should form a filter zone that prevents migration of fine particles from the subgrade into the ballast. In practice, insufficient attention has been placed to sub-ballast gradation historically, and much of the sub-ballast does not adequately perform that function. This notwithstanding, the number of occurrences of subgrade contamination of ballast are relatively few. How Track Fails In a nutshell, track fails when differential rail deflections become excessive. This differential deflection may be expressed in differential elevation between tracks, punching of ties, elastic or plastic deformation of the subgrade, or degradation of ballast. When the bearing capacity of the subgrade is exceeded, the subgrade will deform plastically, resulting in a small amount of permanent deformation under each wheel load. A progressive deterioration of the track begins, as illustrated in Figures 4-7 to 410. It starts with minor deflections and may progress to a fully visible surface heave, where subgrade material is pushed above the elevation of the rail and ties. Under those conditions, ballast drainage is impeded, resulting in further softening and degradation of the subgrade to a point where large, saturated pockets of ballast are trapped in the subgrade. Frost heave and further degradation commonly follow, leading eventually to a severe loss of utility of the track structure.
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Figure 4-7 Stable Site
Figure 4-8 Onset of Instability
Figure 4-9 Growth of Heave
Figure 4-10 Surface Manifestation of Heave
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4.3.4 Instability Instability results when the shear strength of the soil is not sufficient to support the loads applied to it. Bearing capacity failures discussed in the previous section are one type of shear failure that occurs when the soil cannot sustain vertical load applied to it and vertically downward movement results. The term landslide is used to define all types of mass movement of soil or rock, where the mass moves down slope under the influence of gravity only. There are many types of landslides, but the distinguishing feature is that a mass of material is moved and gravity is the driving force. Main Features of Landslides The diagnostic features of most landslides include a scarp that forms at the head of the landslide. This is usually a near vertical wall of soil, usually freshly exposed by movement. The slump blocks are unique, identifiable blocks of soil, usually bounded by scarps that show both vertical and horizontal movement. The main body of the slide is the mass of soil that is pushed ahead by the slump blocks, and may be marked by numerous tension cracks. Bulging of the soil, and thrusting of the slide debris over the natural surface usually mark the toe of the slide. The slip plane or shear zone is usually a distinct and identifiable plane that marks the lower limit of movement and the upper limit of undisturbed soil. It should be noted that the shear zone is not usually planar, but rather may be circular, or a composite curvilinear surface that passes through the weakest zones in the subsurface. Slides that Affect the Track Instability that affects the track can be classified according to the impact that it has on the track. These are described in various illustrations. §
Figure 4-11 illustrates a slide that encompasses a track and will disrupt the track by cutting the alignment. Once the track moves out of line, it is no longer serviceable.
Figure 4-11 Slides Cutting Track
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Figure 4-12 illustrates the effect of a landslide upslope where the toe crosses the track, burying it in under slide debris.
Figure 4-12 Slides Covering Track
§
Figure 4-13 shows the track being heaved up in response to upward movement of the toe of a landslide.
Figure 4-13 Slides Heaving Track
§
Figure 4-14 illustrates an event where a landslide threatens the track, perhaps by encroaching on the down slope shoulder.
Figure 4-14 Slides Threatening Track
§
Figure 4-15 illustrates how base failure in fills on soft foundations can cause the fill to spread and settle. While this may be mistaken as settlement, it is actually a shear movement involving the foundation soils. It is common on organic terrain and other soft foundations.
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Figure 4-15 Base Failure
§
Figure 4-16 shows how locations over old landslides may be reactivated due to a change in stresses within the landslide mass. Many of the ancient landslides are extremely large, and the limits of the landslides may be difficult to detect.
Figure 4-16 Reactivation of Old Slide
Triggering Mechanisms The stability of a slope is dependent upon: §
The shear strength of the soils.
§
Porewater pressure within the soils that make up the slope (this can be roughly measured by knowing the water table).
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The geometry of the slope, particularly the slope angle and changes of slope.
§
Any surcharge loading such as fill or bank widening material stored on the slope or train loads.
Landslides occur either as a result of reduction in soil strength or an increase in the loading on the slope. Reductions in soil strength can occur as the result of: §
An increase in porewater pressure, reducing the available shear strength of the soil. In the case of moisture sensitive soils, the amount of water needed to cause this
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Drainage The three most important elements in good track are: #1 Drainage, #2 Drainage and #3 Drainage – Darrell Cantrell, Engineer Track (Retired) BNSF
D
rainage is the subject of stormwater behavior as it relates to the properties of hydrology and hydraulics. This is a subject that is constantly being reviewed on a regular basis within the regulatory bodies of government and it is therefore always important to review local requirements to guide the engineer through the design process. Even though one method of analysis may be appropriate to use in an area one feels comfortable in, it may not be appropriate in another location. A good rule of thumb is to contact the local highway department as a starting point and continue your investigation to local authorities. The other primary source for the Engineer is the AREMA Manual for Railway Engineering, Chapter 1, Parts 3 & 4. The engineer needs to be aware that one has to maintain existing drainage patterns and not increase headwaters upstream or downstream. Adjacent property owners, whether they are farmers or city dwellers, have certain rights and are protected under common law concerning storm water conveyance and elevation as it relates to property damage.
5.1 Hydrology For the purposes of this Guide, Hydrology will be defined as the study of rainfall events (inches or inches per hour) and runoff (cubic feet per second) as related to the engineering design of conveyance features such as ditches and culverts. These conveyance features are typically designed to a particular storm event or storm frequency. In other words, a storm water conveyance feature is going to be associated with a certain amount of risk with respect to failure. For instance, a 100 year storm return period has a 1% probability of occurring in any given year, a 50 year storm has a 2% probability of occurring in any given year, and a 10 year storm has a 10% chance of occurring in any given year. So it is up to the designer to assign a certain amount of
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5.3 Recommended Procedures 5.3.1 Existing Drainage Study Before proceeding with the design of the project, it should be realized that it is always important to visit the actual project site and identify problems that may be encountered. Existing culverts always seem to be a problem and should be looked at carefully. Examples of potential problems include excessive ditch scouring and constant ponding of water along a ditch system. Railway ditches are typically very flat and do not drain well. However, the designer should always review the situation as if there is a solution. If it is economically feasible to remedy the situation, then the area should be regraded and repaired to what is recognized as common engineering practice. Below is a recommended approach to an existing consistent drainage study: •
Utilize a USGS Quadrangle Map or a Hydrologic Atlas (HA) for the area.
•
Plot existing and proposed railway right-of-way.
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Identify floodplain and floodway boundaries.
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Identify watershed areas based upon contour interpretation.
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Identify existing bridges, culverts and problem areas.
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Identify sheet and concentrated flow.
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Identify closed drainage systems.
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Select outlet points for each watershed area.
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Select the proper hydrology criteria (i.e. rainfall, frequency, formula, etc.).
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Calculate or run the model and assign flow rates to each of the watersheds.
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Add flow rates and hydrographs, as necessary, to determine proper flow through the watershed.
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Select the proper hydraulic method to determine storm water elevations.
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Conduct a plan-in-hand field review.
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Remember the existing drainage study is the benchmark study on which all proposed drainage features are based.
5.3.2 Proposed Drainage System The proposed drainage system typically addresses impacts to an existing man made or natural drainage system from a proposed improvement. This can take the form of new ditches and culverts or it can take the form of improving existing problem areas. Keep in mind that any improvement to an existing drainage system will more than likely affect surrounding drainage patterns and elevations on adjacent or downstream properties. For example, increasing the size of an existing cross culvert introduces more storm water flow rate to downstream property owners. The designer should determine whether this situation is going to present a problem. Below is a recommended approach to the design of a proposed drainage system: •
Complete and review the existing drainage study.
•
Superimpose the proposed improvements on a copy of the existing drainage study map.
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Locate new drainage features such as ditches, bridges and culverts.
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Are there floodplain and wetland impacts?
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Never relocate an existing outlet point unless it is absolutely necessary.
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Try to maintain existing watershed limits (sometimes these do change).
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Calculate the new hydrology for the watershed.
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Calculate the new hydraulics for the watershed.
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Compare the new data with the existing data at the same points.
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Initiate Permitting process.
For adjacent properties, it is ideal to obtain the same results between existing and proposed conditions and it may take a few iterations to obtain those results. Sometimes it is impossible for this to occur. By studying the upstream and downstream effects, the designer may be able to apply a certain amount of change that does not harm or cause damage to adjacent property owners. For example, a 0.1’ or a 0.5’ increase in headwater may be acceptable, or a 5% increase in flow velocity may be acceptable if the surrounding soil conditions are tolerable. There may be more
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considerations to review. However, this is dependent upon the conditions and regulations unique to that project location.
5.3.3 Floodplain Encroachment Evaluation The floodplain is identified by criteria established by the Federal Emergency Management Agency (FEMA) for the 100-year and 500-year storm events or known depression flood prone areas. Typically, the 100-year base flood elevation is the most commonly regulated stormwater elevation associated with rivers, streams and concentrated flow areas. FEMA, State Water Resource Departments, counties and local communities (that are part of the National Flood Insurance Program) closely monitor flood plain areas. Any change to the flood plain will generally result in extensive studies and computer modeling to be submitted for approval. Below is a summary of possible floodplain permitting reviews. FEMA: •
Physical Map Change (Extensive Floodplain Revisions)
•
Letter of Map Revision (Typical Floodplain Revisions)
•
Conditional Letter of Map Revision (Typical Floodplain Revisions done in the design phase)
•
Elevation Criteria (Typically for building structures)
US Army Corps of Engineers: •
Excavation below normal water elevation
State Water Resource Department: •
Floodway (Area within a floodplain that demonstrates conveyance)
County (Some counties may not be involved in the review process): •
Floodplain
•
Floodway
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Compensatory Storage (Excavation required to compensate for floodplain filling)
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Elevation Criteria (Typically for building structures)
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Chapter
Railway Track Design Basic considerations and guidelines to be used in the establishment of railway horizontal and vertical alignments.
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he route upon which a train travels and the track is constructed is defined as an alignment. An alignment is defined in two fashions. First, the horizontal alignment defines physically where the route or track goes (mathematically the XY plane). The second component is a vertical alignment, which defines the elevation, rise and fall (the Z component). Alignment considerations weigh more heavily on railway design versus highway design for several reasons. First, unlike most other transportation modes, the operator of a train has no control over horizontal movements (i.e. steering). The guidance mechanism for railway vehicles is defined almost exclusively by track location and thus the track alignment. The operator only has direct control over longitudinal aspects of train movement over an alignment defined by the track, such as speed and forward/reverse direction. Secondly, the relative power available for locomotion relative to the mass to be moved is significantly less than for other forms of transportation, such as air or highway vehicles. (See Table 6-1) Finally, the physical dimension of the vehicular unit (the train) is extremely long and thin, sometimes approaching two miles in length. This compares, for example, with a barge tow, which may encompass 2-3 full trains, but may only be 1200 feet in length. These factors result in much more limited constraints to the designer when considering alignments of small terminal and yard facilities as well as new routes between distant locations. The designer MUST take into account the type of train traffic (freight, passenger, light rail, length, etc.), volume of traffic (number of vehicles per day, week, year, life cycle) and speed when establishing alignments. The design criteria for a new coal route across the prairie handling 15,000 ton coal trains a mile and a half long ten times per day will be significantly different than the extension of a light rail (trolley) line in downtown San Francisco.
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curves as D (degrees per 20 meter arc). However, there does not seem to be any widespread incorporation of this practice. When working with light rail or in metric units, current practice employs curves defined by radius. As a vehicle traverses a curve, the vehicle transmits a centrifugal force to the rail at the point of wheel contact. This force is a function of the severity of the curve, speed of the vehicle and the mass (weight) of the vehicle. This force acts at the center of gravity of the rail vehicle. This force is resisted by the track. If the vehicle is traveling fast enough, it may derail due to rail rollover, the car rolling over or simply derailing from the combined transverse force exceeding the limit allowed by rail-flange contact. This centrifugal force can be counteracted by the application of superelevation (or banking), which effectively raises the outside rail in the curve by rotating the track structure about the inside rail. (See Figure 6-6) The point, at which this elevation of the outer rail relative to the inner rail is such that the weight is again equally distributed on both rails, is considered the equilibrium elevation. Track is rarely superelevated to the equilibrium elevation. The difference between the equilibrium elevation and the actual superelevation is termed underbalance. Though trains rarely overturn strictly from centrifugal force from speed Figure 6-6 Effects of Centrifugal Force (they usually derail first). This same logic can be used to derive the overturning speed. Conventional wisdom dictates that the rail vehicle is generally considered stable if the resultant of forces falls within the middle third of the track. This equates to the middle 20 inches for standard gauge track assuming that the wheel load upon the rail head is approximately 60-inches apart. As this resultant force begins to fall outside the two rails, the vehicle will begin to tip and eventually overturn. It should be noted that this overturning speed would vary depending upon where the center of gravity of the vehicle is assumed to be. There are several factors, which are considered in establishing the elevation for a curve. The limit established by many railways is between five and six-inches for freight operation and most passenger tracks. There is also a limit imposed by the Federal Railroad Administration (FRA) in the amount of underbalance employed, which is generally three inches for freight equipment and most passenger equipment.
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Underbalance limits above three to four inches (to as much as five or six inches upon FRA approval of a waiver request) for specific passenger equipment may be granted after testing is conducted.
T R A C K
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EQUILIBRIUM
OVERBALANCE
Center of Gravity
Gravity
Centrifugal Force
UNDERBALANCE
Centrifugal Force Center of Gravity
Center of Gravity
Centrifugal Force
Resultant
Resultant Gravity
Superelevation
Resultant
Superelevation
Gravity
Superelevation
Ea + 3 Amount of Track is rarely elevated to Vmax = 0.0007 D Underbalance equilibrium elevation V max = Maximum allowable operating speed (mph). because not all trains will Ea = Average elevation of the outside rail (inches). be moving at equilibrium = Degree of curvature (degrees). D speed through the curve. Figure 6-7 Overbalance, Equilibrium and Underbalanced Furthermore, to reduce both the maximum allowable superelevation along with a reduction of underbalance provides a margin for maintenance. Superelevation should be applied in 1/4-inch increments in most situations. In some situations, increments may be reduced to 1/8 inch if it can be determined that construction and maintenance equipment can establish and maintain such a tolerance. Even if it is determined that no superelevation is required for a curve, it is generally accepted practice to superelevate all curves a minimum amount (1/2 to 3/4 of an inch). Each railway will have its own standards for superelevation and underbalance, which should be used unless directed otherwise.
The transition from level track on tangents to curves can be accomplished in two ways. For low speed tracks with minimum superelevation, which is commonly found in yards and industry tracks, the superelevation is run-out before and after the curve, or through the beginning of the curve if space prevents the latter. A commonly used value for this run-out is 31-feet per half inch of superelevation. On main tracks, it is preferred to establish the transition from tangent level track and curved superelevated track by the use of a spiral or easement curve. A spiral is a curve whose degree of curve varies exponentially from infinity (tangent) to the degree of the body curve. The spiral completes two functions, including the gradual introduction of superelevation as well as guiding the railway vehicle from tangent track to curved track. Without it, there would be very high lateral dynamic load acting on the first portion of the curve and the first portion of tangent past the curve due to the sudden introduction and removal of centrifugal forces associated with the body curve. There are several different types of mathematical spirals available for use, including the clothoid, the cubic parabola and the lemniscate. Of more common use on railways are the Searles, the Talbot and the AREMA 10-Chord spirals, which are empirical approximations of true spirals. Though all have been applied to railway applications to 224
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6.4 Alignment Design In a perfect world, all railway alignments would be tangent and flat, thus providing for the most economical operations and the least amount of maintenance. Though this is never the set of circumstances from which the designer will work, it is that ideal that he/she must be cognizant to optimize any design. From the macro perspective, there has been for over 150 years, the classic railway location problem where a route between two points must be constructed. One option is to construct a shorter route with steep grades. The second option is to build a longer route with greater curvature along gentle sloping topography. The challenge is for the designer to choose the better route based upon overall construction, operational and maintenance criteria. Such an example is shown below.
Figure 6-9 Heavy Curvature on the Santa Fe - Railway Technical Manual – Courtesy of BNSF
Suffice it to say that in today’s environment, the designer must also add to the decision model environmental concerns, politics, land use issues, economics, long-term traffic levels and other economic criteria far beyond what has traditionally been considered. These added considerations are well beyond what is normally the designer’s task of alignment design, but they all affect it. The designer will have to work with these issues occasionally, dependent upon the size and scope of the project.
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On a more discrete level, the designer must take the basic components of alignments, tangents, grades, horizontal and vertical curves, spirals and superelevation and construct an alignment, which is cost effective to construct, easy to maintain, efficient and safe to operate. There have been a number of guidelines, which have been developed over the past 175 years, which take the foregoing into account. The application of these guidelines will suffice for approximately 75% of most design situations. For the remaining situations, the designer must take into account how the track is going to be used (train type, speed, frequency, length, etc.) and drawing upon experience and judgment, must make an educated decision. The decision must be in concurrence with that of the eventual owner or operator of the track as to how to produce the alignment with the release of at least one of the restraining guidelines. Though AREMA has some general guidance for alignment design, each railway usually has its own design guidelines, which complement and expand the AREMA recommendations. Sometimes, a less restrictive guideline from another entity can be employed to solve the design problem. Other times, a specific project constraint can be changed to allow for the exception. Other times, it’s more complicated, and the designer must understand how a train is going to perform to be able to make an educated decision. The following are brief discussions of some of the concepts which must be considered when evaluating how the most common guidelines were established. A freight train is most commonly comprised of power and cars. The power may be one or several locomotives located at the front of a train. The cars are then located in a line behind the power. Occasionally, additional power is placed at the rear, or even in the center of the train and may be operated remotely from the head-end. The train can be effectively visualized for this Figure 6-10 Automatic Coupler discussion as a chain lying on a table. We will assume for the sake of simplicity that the power is all at one end of the chain. Trains, and in this example the chain, will always have longitudinal forces acting along their length as the train speeds up or down, as well as reacting to changes in grade and curvature. It is not unusual for a train to be in compression over part of its length 233
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(negative longitudinal force) and in tension (positive) on another portion. These forces are often termed ‘buff’ (negative) and ‘draft’ (positive) forces. Trains are most often connected together with couplers (Figure 6-10). The mechanical connections of most couplers in North America have several inches (up to six or eight in some cases) of play between pulling and pushing. This is termed slack. If one considers that a long train of 100 cars may be 6000' long, and that each car might account for six inches of slack, it becomes mathematically possible for a locomotive and the front end of a train to move fifty feet before the rear end moves at all. As a result, the dynamic portion of the buff and draft forces can become quite large if the operation of the train, or more importantly to the designer, the geometry of the alignment contribute significantly to the longitudinal forces. As the train moves or accelerates, the chain is pulled from one end. The force at any point in the chain (Figure 6-11) is simply the force being applied to the front end of the chain minus the frictional resistance of the chain sliding on the table from the head end to the point under consideration.
Figure 6-11 Force Applied Throughout the Train - ATSF Railroad Technical Manual - Courtesy of BNSF
As the chain is pulled in a straight line, the remainder of the chain follows an identical path. However, as the chain is pulled around a corner, the middle portion of the chain wants to deviate from the initial path of the front-end. On a train, there are three things preventing this from occurring. First, the centrifugal force, as the rail car moves about the curve, tends to push the car away from the inside of the curve. When this fails, the wheel treads are both canted inward to encourage the vehicle to maintain the course of the track. The last resort is the action of the wheel flange striking the rail and guiding the wheel back on course. Attempting to push the chain causes a different situation. A gentle nudge on a short chain will generally allow for some movement along a line. However, as more force is applied and the chain becomes longer, the chain wants to buckle in much the same way an overloaded, un-braced column would buckle (See Figure 6-12). The same theories that Euler applied to column buckling theory can be conceptually applied to a train under heavy buff forces. Again, the only resistance to the buckling force becomes the wheel/rail interface.
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Chapter
Communications and Signals Types, Theory of Operation and Design Considerations of Train Control and Railway Communications and Signals Systems.
T
his chapter contains a basic description of the types and theory of operation of Communications and Signals Systems, their application and design considerations. Due to the safety sensitive nature of these systems, the examples and/or sample formulas included should not be incorporated into actual designs. Readers of this chapter are invited to read the AREMA Communications and Signals Manual of Recommended Practices for a comprehensive study of the various elements of signaling, including recommended practices.
7.1 Introduction to Signals 7.1.1 Railway Operation In the early days of railway operation, there was seldom need for more than one train to operate on a section of track at any given time. As traffic increased, it became necessary to operate trains in both directions over single track. To permit faster and superior trains to pass and provide for opposing trains to meet, it was necessary to construct sidings. It was then necessary to devise methods to affect opposing and passing movements without disaster and with a minimum of confusion and delay. This was achieved by introducing time schedules so that the meeting and passing of trains could be prearranged. Thus, the "timetable" was born.
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The rails of a track circuit provide the path for the flow of current from the battery. Bond wires are applied to ensure a path of low and uniform resistance between adjoining rails. Insulated joints define track circuit limits. Track circuits vary in length as required. AREMA definitions of terms commonly applied to track circuit operation are: Ballast Leakage:
ballast, ties, etc.
The leakage of current from one rail to the other rail through the
Ballast Resistance:
The resistance offered by the ballast, ties, etc., to the flow of leakage current from one rail of the track to the other rail.
Floating Charge:
Maintaining a storage battery in operating condition by a continuous charge at a low rate. Rail Resistance:
connections.
The total resistance offered to the current by the rail, bonds and rail
A low resistance connection across the source of supply, between it and the operating units. Shunt Circuit:
Short Circuit:
A shunt circuit abnormally applied.
Shunting Sensitivity:
The maximum resistance in ohms, which will cause the relay contacts to open when the resistance is placed across the rails at the most adverse, shunting locations.
7.3.2 Track Circuit Operation A battery is connected to one end of the track circuit, close to the insulated joints, with positive energy applied to the south rail “S” and negative to the north rail “N.” The relay is connected at the other end of the track circuit with one lead of the relay coils going to rail “S” and the other to rail “N.” With the battery and relay connected, current has a complete path in which to flow, as indicated by the arrows.
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N Insulated Joints
Rails S
Lightning Arrestor
Series Resistor
Limiting Resistor
Relay Battery Figure 7-14 Conventional DC Track Circuit Basics
The track circuit is designed as a series circuit, but because of ballast leakage, many high resistance paths exist from rail to rail. When an alternate path for current flow exists from one rail to the other via the ballast, the track circuit becomes a parallel circuit. The current through each ballast resistance and the current through the relay coils adds up to the total current drain from the battery during normal conditions. When a train enters a track section, the wheels and axles place a shunt (short) on the track circuit. This creates a low resistance current path from one rail to the other and in parallel with the existing ballast resistance and relay coil. When maximum current from the battery is reached because of current flow through the relay coils, ballast resistance and low resistance path created by the train shunt, the relay armature drops. Most of the current flows through the low resistance shunt path. This reduces the current in the relay sufficiently to cause the armature to drop, thereby opening the front contacts. In Figure 7-15, the heavy dark arrows indicate the high current path through the shunt.
TR
R
G
Figure 7-15 Contacts of a DC Track Circuit Relay Controlling a Lighting Circuit 281
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In Figure 7-15, the front contact of the relay is inserted in a signal control circuit to operate a green signal and the back contact to operate the red signal. When a train is present on that section of track, the relay de-energises and the heel contact makes with the back contact lighting the red signal. When the last pair of wheels moves off the track circuit, the current will again flow in the un-shunted track circuit, through the coils of the relay, causing the front contacts to close and light the green signal. An appreciation of the effect of ballast resistance is necessary to understand track circuit operation. When good ties are supported in good crushed stone and the complete section is dry, the resistance to current flow from one rail to the other rail is very high. This condition is known as maximum ballast resistance and is ideal for good track circuit operation. When the ballast is wet or contains substances such as salt or minerals that conduct electricity easily, current can flow from one rail to the other rail. This condition is minimum ballast resistance. With minimum ballast resistance, ballast leakage current is high. When the ballast resistance decreases significantly, the relay can be robbed of its current and become de-energized, or fail to pick up after it has been de-energized by a train and the train has left the track circuit. Because the ballast resistance varies between a wet day (minimum ballast resistance) and a dry day (maximum ballast resistance) the flow of current from the battery will vary. When a train occupies a track circuit, it places a short circuit on the battery. In order to limit the amount of current drawn from the battery during this time, a resistor is placed in series with the battery output to prevent the battery from becoming exhausted. A variable resistor is used in order to set the desired amount of discharge current during the period the track circuit is occupied. This resistor is called the “battery-limiting resistor.” When the battery-limiting resistor is adjusted as specified, higher current will flow through the relay coil on a dry day due to maximum ballast resistance. If this current is too high the relay will be hard to shunt. To overcome this condition a variable resistor is inserted in series with the relay coil at the relay end of the track circuit and is used to adjust the amount of current flowing in the relay coils.
7.3.3 Train Shunting Relay drop-away time on train shunt is dependent on the following factors:
• •
The relay current before the shunt is applied The effectiveness of the shunt
When a train occupies and shunts a track circuit, the relay will not drop immediately. The magnetic field that built up around the cores when the relay was energized must
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Motor Gear train Hold clear mechanism Circuit controller
Counterweights are used in conjunction with various lengths of gate arms for the purpose of off-setting the weight of the gate arm itself, in order that the motor without excessive current draw can raise the gate. Counterweights:
The counterweights are adjustable in two ways to provide a sufficient number of footpounds of torque in both the vertical and horizontal positions. Counterweights are to be installed as per manufacturer's instructions. Gate arms are to be torqued in the vertical and horizontal position according to the manufacturer's handbook, which is included with each mechanism. Settings may vary depending on which type of gate model is used. The light nearest the tip of the gate arm is at the prescribed distance from the tip and burns steadily as per the railway’s standards. The other lights are located to suit local conditions and flash alternately in unison with the lights on the gate mast. Gate Lighting:
When positioning the lights on the gate arm, the rightmost light must be in line with the edge of the roadway and the center light should be placed between the two outer lights.
7.5.3 Crossing Motion Detector/Predictor On a crossing equipped with a motion detector, the crossing warning device will activate as soon as a train is detected. If the train stops or backs up, the crossing warning device will stop operating. The industry has taken it one step further by converting the motion sensor into a device that can predict the speed of an oncoming train to activate the crossing at a pre-determined time. The automatic warning device is hardware and software driven.
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Termination shunt TX RX Figure 7-30 Bi-directional - Automatic Crossing Warning Device
There are several configurations to choose from. The above example illustrates a bidirectional configuration. A key function of the transmitter section is to maintain a constant AC current on the track. The transmitter wires (TX) send an AC signal:
• • •
Down one rail in both directions (bi-directional) Through the termination shunt at the ends of the circuit Through the other rail, returning to the AC source
The receiver wires (RX) define the limits of the island circuit and monitor the transmitter signal. Track impedance, in the form of inductive reactance (resistance to AC), depends on the length of the track circuit, which is defined by the termination shunt and the applied frequency. For this reason, the longer approach circuits should use a low frequency, while the shorter island tracks should use a higher frequency. With no train on either approach, the electronic box at the crossing creates a 10-volt DC signal (distant voltage). When a train comes onto the crossing approach, the following occurs:
• • • •
Lead axle shunts the track. Lead axle becomes a moving termination shunt, which shortens the track circuit as it approaches the crossing. Track impedance (resistance) decreases as the track circuit shortens. As the track impedance decreases, the distant voltage (10 VDC) decreases towards 0 volts at the crossing.
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•
As the train leaves the crossing, the distant voltage rises again towards 10 VDC. The rate of voltage drop is dependent on the speed of a train. From this, you can probably see that with a little creative programming, the box can predict the speed of a train and activate the crossing at the appropriate time or stop the crossing operation if the train stops or backs up. For this configuration (bi-directional), no insulated joints are required. However, if there are insulated joints because of the presence of a DC track circuit, bypass couplers can be used to allow the AC signal around the joints while blocking DC. Output terminals from the crossing predictor provide 12 volts DC to the crossing control circuits. The crossing control circuits are either relay logic control circuits or solid-state control circuits. Crossing control circuits operate the bell, flashing lights and gate arms.
7.6 Centralized Traffic Control (CTC) Centralized Traffic Control (CTC) permits both opposing and following moves of trains on the same track by the indication of block signals. CTC allows for more than one train to be in a block, travelling in the same direction at the same time and eliminates the need for train orders and timetable superiority. Control point circuitry, controlled block signals, dual control power operated switch machines, electric locks in conjunction with switch circuit controllers and advanced communications systems are all integral parts of a CTC system. Signal indications authorize train movement in CTC. Once a train is allowed into a block by the dispatcher (control signal often referred to as home signal), the train is controlled by automatic block signals (intermediate signals). Important Note: The sequence of operations described below is a typical model only. For compliance to FRA requirements and regulations refer to Parts 235 and 236.
7.6.1 Operation Many existing CTC systems are relay based. Modern installations are microprocessor based with solid-state support circuits and advanced communication links. For this discussion, we will consider a relay-based system. A later section of this chapter will introduce solid-state systems. Control and indication codes rely on step-by-step operation of relays and mechanisms at the field location, working in synchronism with step-by-step operation of relays at the control office.
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CTC systems are controlled by a dispatcher with code and carrier systems, which provide communications to the field control points with two line wires and/or by microwave signals, regardless of the number of control points. To transmit a control, the dispatcher positions the necessary levers and buttons on the control machine. Next, he pushes the appropriate start button that causes a code to be transmitted. All field locations connected to the code line see the control code, but only the one called is selected. At the selected location, the control portion of the code is delivered through field application relays to cause the function relays to operate switches, signals, etc. Control Codes:
When a field change occurs in the position of a switch, the aspect of a signal, or the condition of a track circuit, an indication code is set up at the field location, which in turn automatically transmits the indication back to the control office. When the indication code is received at the control machine, the appropriate indications light up on the dispatcher’s panel to show the conditions existing at the field locations. Indication Codes:
Control Points may consist of a single switch or a cross-over between tracks, or various combinations of switches and crossovers with associated signals. From the control machine, the dispatcher remotely controls the power switch machines. A network of signals is associated with each power switch to ensure that train movements are made safely. CTC is basically a series of controlled switches and signals at wayside locations, connected with automatic signalling.
Control Point:
Control Office:
Each train dispatcher is responsible for the operation of traffic on his/her assigned territory. A dispatcher's duties require that he set up routes and signals for traffic, arrange meets of trains and provide protection for roadway workers.
Railways have implemented computers to assist with train control systems. The computers are equipped with mass storage devices on which train and signal activity are archived for future reference. This information is accessed for purposes ranging from accident investigation to train delay reports. The dispatching computers are located in a special room. This room contains an air conditioning system to keep the environment at a constant temperature and humidity, and a fire protection system to safeguard against fires in and around the computer room. As well, the system is equipped with an un-interruptible power supply (UPS) to keep it up and running in the event of a commercial power failure. The uninterruptible power supply is made up primarily of storage batteries and a diesel generator. The generator is used to keep the batteries fully charged if the power failure persists. The computer duplicates all of the interlocking checks performed by the field circuitry, safeguarding against any potentially unsafe requests by any of the system users.
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This chapter contains a basic description of the types of railway structures and their design considerations. The purpose is to inform engineers of design considerations for railway structures that are different from their non-railway counterparts. Due to variations in design standards between the different railways, consult the controlling railway for their governing standard before starting design.
8.1 Introduction to Railway Structures Railway structures encompass a wide array of construction intended to support the track itself or house railway operations. Common examples of track carrying structures are bridges, trestles, viaducts, culverts, scales, inspection pits, unloading pits and similar construction. Examples of common ancillary structures are drainage structures, retaining walls, tunnels, snow sheds, repair shops, loading docks, passenger stations and platforms, fueling facilities, towers, catenary frames and the like. While the design of ancillary structures for the railway environment may introduce considerations not found in their non-railway counterparts, these considerations are usually well defined in the governing railway’s standards. Accordingly, this chapter will focus primarily on track carrying structures. When designing railway structures, the various sources of their loads must be considered, as they would be with any other similar, nonrailway structure. In addition to the dead load of the structure itself, there are the usual live loads from the carried traffic. To these are added the dynamic components of the traffic such as impact, centrifugal, lateral and Figure 8-1 Typical Railway Bridge - Courtesy of Metra longitudinal forces. Then there are the environmental considerations such as wind, snow and ice, thermal, seismic and stream flow loads. Finally, because railway structures must perform under
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heavier loads, have longer service lives, and dissimilar maintenance constraints compared to their highway counterparts, other factors, including fatigue and maintenance issues, tend to influence railway structure design more than roadway structures. Once the designer has established the first pass at the load environment for the subject structure, the primary difference between a highway structure and a railway structure should become obvious. In the typical railway structure, the live load dominates all of the other design considerations. For the engineer accustomed to highway bridge design, where the dead load of the structure itself tends to drive the design considerations, this marks a substantial divergence from the norm. Specifically, the unacceptability of high deflections in railway structures, maintenance concerns and fatigue considerations render many aspects of bridge design common to the highway industry unacceptable in the railway environment. Chief among these are welded connections and continuous spans.
8.2 Major Bridge Components30 In general terms, the major components of track carrying structure are very similar to their non-railway counterparts. In addition to the types of construction, the engineer must also choose from among the available material alternatives. Generally, these are limited to timber, concrete and steel, or a combination of the three. Exotic materials can also be considered, but they are beyond the scope of this book. Each material has its specific advantages. Timber is economical, but has strength and life limitations. Structural timber of the size and grade traditionally used for railway structures is getting more difficult to obtain at a price competitive with concrete or steel. Concrete is also economical, but its strength to weight ratio is poor. Steel has a good strength to weight ratio, but is expensive. The material chosen for the spans will generally determine the designation of the bridge. For instance, steel beam spans on timber piles will be considered a steel bridge. The point where one form of construction with a certain type of material becomes advantageous over another is a matter of site conditions, span length, tonnage carried and railway preference. While initial cost of construction is a major point in the decision process, the engineer must keep in mind such additional factors as construction under traffic and the long-term maintainability of the final design.
Selected materials from “Railway Track & Structures Cyclopedia,” 1955 Edition, Simmons-Boardman Publishing Company
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The nature of the obstacle being crossed will drive most superstructure design decisions with the ultimate goal to achieve the least overall lifecycle cost for the structure. For short (height) structures, trestle construction is favored due to the economies of pile bents. Conversely, taller structures over good footing are likely to be viaducts with longer spans supported by towers. Where there is insufficient clearance over navigable waterways, moveable spans may be necessary. The addition of longer or moveable spans to clear main channels does not significantly affect the design of the balance of the structure. However, as the structure becomes taller, the economies of pile bents are diminished due to the need to strengthen the relatively slender components. The alternative to conventional trestle construction is trestle on towers, otherwise known as viaducts. Trestle on towers can offer a significant reduction in footprint for only a moderate increase in span requirements. It is customary for the spans to be of alternating lengths, with the short span over the tower equal to the leg spacing at the top of the tower. This ensures that each span remains a simple span with full bearing at the ends of the span. Of course, trestle construction represents the typical site conditions. More demanding site conditions may require exotic solutions. For example, very tall, very short (length) conditions may lend themselves to arch construction, whereas for transit operations, very long main span requirements may lend themselves to suspension type construction and some trestles on towers may be better constructed as a series of arches.
8.2.3 Bridge Deck The bridge deck is that portion of a railway bridge that supplies a means of carrying the track rails. In comparison to the rest of the superstructure design, bridge deck decisions are relatively simple. The choices are open deck and ballast deck. On open deck bridges (Figure 85), the rails are anchored directly to timber bridge ties supported directly on the floor system of the superstructure. On ballasted bridge Figure 8-5 Open Deck Structure - Courtesy of Canadian decks, the rails are anchored directly National to timber track ties supported in the ballast section. The ballasted bridge decks require a floor to support the ballast section and such floors are designated by their types, such as timber floors, structural plate floors, buckle plate floors or concrete slab floors, all of which transfer loads directly to the superstructure.
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Variations from the two general types of bridge deck construction consist of track rails anchored directly to steel or concrete-slab superstructures (direct fixation) and the several types of concrete-encased beam spans or concrete-filled steel-trough superstructures on which the ballast section is placed. The latter types of structures have many examples still in service today, but are not generally cost-effective for new construction. Some might consider the notion of bridge railings to be an odd bridge design consideration. Railway bridges traditionally have not been designed for the conveyance of anything other than railway traffic, which does not in and of itself, require any sort of railing whatsoever. Recently, however, a greater focus upon railway worker safety has resulted in railings being widely incorporated. Open Bridge Decks Many different considerations enter into the choice of open or ballast decks, and the selection usually is governed by the requirements of each individual structure. Open decks are less costly and are free draining (Figure 8-6), but their use over streets and highways requires additional measures such as canopies, plates or wooden flooring Figure 8-6 Open Deck Bridge - Courtesy of Metra to protect highway traffic from falling objects, water or other materials during the movement of trains. Open-deck construction establishes a permanent elevation for the rails. Normal surfacing and lining operations, particularly in curves, eventually result in line swings leading into the fixed bridge. The grade frequently is raised to the extent that the bridge eventually becomes low. The bridge dumps are of a different modulus than the rigid deck. Thus, it becomes difficult to maintain surface off of the bridge as well. This equates to extensive maintenance costs that shortly will surpass the first cost savings gained by installing an open deck bridge over a ballast deck bridge. In welded rail, tight rail conditions can occur at the fixed ends of an open deck bridge, thus requiring an increased level of surveillance in hot weather. Requirements for Ties For ballast deck structures, bridge ties are no different than those found in traditional track construction. However, in track constructed with concrete ties, the track is often times transitioned to timber ties before crossing the structure. Some railway companies and agencies have had difficulty with fouled ballast, track alignment and deck surface damage resulting from the use of concrete ties on bridges. Individual railway
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fastened with metal straps to the bottoms of bridge ties to bring all ties to the required surface. Procedures for dapping and/or shimming ties for superelevation are covered in Chapter 7 of the AREMA Manual for Railway Engineering, Section 1.14.7. Ballasted Decks A ballasted deck (Figure 8-7) provides a better riding track. The track modulus is consistent on the dumps of the bridge as well as across the bridge. Thus, one is unlikely to have surface runoff problems on the bridge dumps. Surfacing and lining operations can continue across the bridge unimpeded. However, care must be exercised to maintain a permanent grade line in the vicinity of and over Figure 8-7 Ballast Decked Bridge. – Courtesy of Canadian National a ballasted deck bridge to be certain that excessive quantities of ballast are not accumulated on the bridge structure through track raises during successive reballasting operations. Ballasted decks (Figure 8-8), irrespective of the type of bridge floor, afford a considerable measure of protection to the steel floor system against damage from derailed car wheels traveling across the bridge. Over roadways, vehicles and the public are protected from dropping ballast and material off of the cars. Ballast The depth of ballast contributes to the satisfactory functioning of ballasted decks on railway bridges. It is generally agreed that 6 inches to 12 inches of ballast under the ties is adequate and that more than 12 inches is undesirable because of the potential of overload involved, except when provision is made in the design for a greater load. Many designers calculate the dead load on the basis of 18 inches to 24 inches of ballast to accommodate future raises.
Figure 8-8 Ballast Decked Structure - Courtesy of Metra
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8.5 Structural Design Considerations 8.5.1 Introduction With the exception of larger bridges, most highway structures designed for a 50 to 75year service life often begin to reach their practical service life at about 30 years of age. Though this is commonly a result of increases in traffic or higher safety standards, the ability to perform major repairs or upgrades of highway structures by temporary removal of the bridge from service is generally not a significant concern. Railway bridges, on the contrary, are designed to have a significantly longer life, and indeed, a considerable number of railway structures in service today are in the neighborhood of 100 years old. Detour routes resulting from failure or significant repair/maintenance efforts are expensive and may not be viable. Though the design criteria within AREMA reflect this consideration, the operating impact and expense must be called to mind when considering the replacement of an existing structure. Often times a designer will have a proposed design solution rebuffed by a railway for this reason. Though the solution offered may be widely accepted in highway design, the permanence required by the railway environment may not have been yet proven to the railway. Railway structures require a much greater consideration of longitudinal loading than a typical highway bridge. This is the result of two environmental variables. Vehicle and individual wheel loads of railway vehicles are many times greater than roadway vehicles. Likewise, unlike roadways, the vehicle running surface (the rail) is continuous between the bridge structure and the adjacent roadbed. The track structure by its very nature is moderately flexible, distributing loads in all directions over a length of track. The introduction of a fixed object (e.g. end of bridge) concentrates this loading to specific points of distribution. When comparing railway bridges to roadway, pedestrian, and other sorts of bridges, the live loading relative to the dead load is much greater and more consistent. This consistent loading and unloading over a greater stress range results in fatigue considerations more prevalent in railway bridge design than other types.
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8.5.2 Bridge Loading32, 33 In the design of any structure, the designer must consider several different load types, including, but not limited to, dead load, live load, wind, weather (snow, ice, etc.), earthquake or any combination there of. Like other governing codes and design organizations including ACI, AISC and AASHTO, AREMA sets forth guidelines for both allowable stress for steel (Chapter 15) and timber (Chapter 7) and load factor design guidelines for concrete (Chapter 8) to be used in the design of structures subject to railway loading. Many of these guidelines are consistent in character, if not identical to other codes. However, there are many distinctions, which are the result of the different service demands of railway structures as well as railway practice or preference developed over the past 150 years. The designer must be cognizant of the fact that each chapter is effectively independent of the others, and not all handle similar design considerations in the same fashion. Where a single structure may incorporate several different types of materials (e.g. a composite structure with steel stringers and a concrete deck), both Chapters 8 and 15 must be referenced throughout the design process. Some other chapters of the AREMA Manual for Railway Engineering may reference one of the structural chapters when addressing structural issues. The reader is also cautioned that the Manual for Railway Engineering is always under revision. The following material is current as of the date this text was published and is provided herein only for general informational understanding. Referencing the latest issue of the Manual for Railway Engineering is essential before undertaking any design activity. Dead Load The dead load consists of the estimated weight of the structural members, plus that of the tracks, ballast and any other railway appendages (signal, electrical, etc.) supported by the structure. The weight of track material (running rails, guard rails, tie plates, spikes and rail clips) is taken as 200 pounds per lineal track foot. Ballast is assumed to be 120 lbs per cubic foot. Treated timber is assumed to be 60 lbs per cubic foot. Waterproofing weight is the actual weight. The designer should allow for additional ballast depth for future grade or surfacing raises (generally 8” – 12”). On ballasted deck bridges, the roadbed section is assumed to be full of ballast to the top of tie with no reduction made for the volume that the tie would include.
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Composite Design The design and use of composite steel and concrete spans for railway bridges is addressed in Section 5.1 of Chapter 15 of the AREMA Manual for Railway Engineering. This type of superstructure comprises a steel beam or girder and a concrete deck slab. The connection between the two materials is designed and constructed to transfer adequate shear force, such that the two materials behave as a single, integral unit under load. The theory of composite design, governing the recommendations in the AREMA Manual for Railway Engineering, is very similar to that found in the working stress method in AASHTO and allowable stress methods in various building codes. Some of the important issues include: §
Selection of the effective flange width of the concrete as a function of slab thickness, steel beam spacing or span length;
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Proportioning of the cross-section by the moment-of-inertia method;
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Application of the dead load forces to the non-composite or composite section, depending on construction sequencing and methods;
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Considering the effect of creep due to long term dead loads acting on the composite section.
Shear connectors may be either steel channels or headed studs welded to the top flange of the steel and embedded in the concrete deck. Reference is made to the AREMA Manual for Railway Engineering or engineering textbooks for specifics on the preceding items. Additional consideration is warranted for railway bridges in other aspects of design, however. One issue to address in composite design is the magnitude of live load to be resisted. Although not specifically addressed in the AREMA Manual for Railway Engineering, railway companies generally require that the steel beams or girders be proportioned to carry without contribution from the concrete deck slab, a Cooper’s live load of only a slightly reduced magnitude than that of the entire structure. For example, a bridge with a composite design load of E-80 is often required to have the steel section alone provide support for an E-60 or higher, and maybe as much as E-80 as well, depending upon the railroad and the type of structure considered. This ensures that if the concrete deck is damaged during a derailment, the steel section will be sufficient to carry rail traffic, even if the concrete must be torn out and an open deck installed. If the steel alone is sized for the design load, the cost savings through efficient use of materials is somewhat less for railway structures than it is for highway and building structures that make full use of the composite section to resist live load and impact.
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The limitation on deflection due to live load plus impact also can usually be waived when considering the steel only for railway bridge design. The full composite section should be designed as being sufficiently stiff to meet the deflection limitations. Even if the steel section is adequate to carry the final design loading without contribution from the concrete slab, composite action still must be investigated. The neutral axis of the composite section will be higher on the cross-section than that for the non-composite section. This will increase the stress range in the material below the neutral axis, and fatigue details should be checked for this increased range. While composite steel and concrete spans provide a stiff design with the benefits of a ballasted-deck bridge, they are unlikely to be used to replace existing structures on existing alignments. Compared to precast concrete deck panels, the additional time required to form, place and cure the cast-in-place concrete deck of a composite span requires off-line construction to minimize impact to rail operations. Parallel construction of a composite span with a lateral roll-in during a train free window is one way to work around this problem. Additionally, since the deck concrete is not under compression from prestressing or post-tensioning, the use of a waterproofing system to protect the deck may be warranted. Where structure depth is limited by vertical clearances below the structure, a steel plate may be used instead of a concrete deck. The steel plate may or may not be included in the beam design, depending on the connection to the beam. Bridge Design Assumptions and Constructibility Issues When planning railway structures, it is imperative to be mindful of the factors that frequently control design and construction. Many in the railway industry would agree, that the driving factor of design and construction is track time. Operations are key, and with greater traffic demands on an ever-aging infrastructure, track time is at a premium. It is important for railways to balance time for operations, maintenance/repair and new construction. The designer is challenged with producing plans and specifications that will yield the best structure in the shortest amount of time. Many times the design efficiency is sacrificed for a shorter construction period. Let’s briefly examine one simple scenario: the superstructure replacement of a short, singlespan bridge. In it’s nearly 100-year life span, the steel superstructure had been raised while being converted from a ballasted deck to an open deck. This conversion included the use of what is known as a grillage. A grillage (also known as cribbing) is a temporary steel support, usually in the form of short sections of steel H-piles, welded together side-by-side to form a shallow (1-2 foot) bearing seat. The steel is subsequently encased in concrete. This technique is most common to rehabilitation projects. When replacing this superstructure, the most efficient design might include cutting the backwall, removing the grillage (thus lowering the beam seat)
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Chapter
RAILWAY ELECTRIFICATION 9.1 Introduction
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espite the competition of airplanes, buses, trucks and cars, trains still play a major transportation role in society, filling specific markets such as high-speed and non-high-speed intercity passenger service, heavy haul of minerals and freight, urban light rail systems and commuter rail. This chapter presents an Figure 9-1 Overhead High Speed Catenary - Courtesy of LTK, Inc. introduction to electrification of rail systems. It is intended to provide a historical perspective and an overview of typical design principles, construction practice, and maintenance considerations. Those interested in learning more are invited to review AREMA’s Manual for Railway Engineering, Chapter 33, Electrical Energy Utilization, and Chapter 17, High Speed Rail Systems, which contain sections devoted to electrification power supplies, traction power systems studies and guidelines for the design of overhead contact systems.
9.2 Development of Motive Power for Railways The earliest recorded tramway served a mine in Germany, beginning in about 1550. The tramway was developed because the rolling resistance of wheels on rails was much less
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Does not create possible electrical safety hazards to the public due to the presence of the bare conductors of the contact system.
When the cost of diesel fuel was 9 cents a gallon and the supply seemed unlimited, United States railways were not interested in alternative methods of propulsion. Railway electrification interest peaks during times of uncertainty in the energy industry. When fuel rose to 34 cents per gallon and the oil embargos occurred, much effort was expended studying alternatives to hydrocarbon fuels. Studies showed that "an estimated 34% savings in energy could be achieved by using electric power. Electrification of just 10% of the (then) present rail trackage (in the densest traffic corridors) could result in a 40% reduction in railway diesel fuel consumption.” Studies made in the 1970’s also showed that approximately 6 years after electrifying a route, the operating cost would break even when compared to the operating cost of diesel service. At 30 years, the annual operating cost of an electrified system would be one-third that of diesel service. In other words, over the effective life of a railway, the cost to operate a diesel-electric system far exceeds that of an electric system. These increased costs mainly come from the price of fuel and maintenance. Diesel locomotives average 3 to 10 gallons or more of fuel per mile and three times the amount of maintenance of straight electric locomotives. The most significant aspect arising from these studies is that in order to realize the long-term savings, a huge capital investment is needed. Even when engineering economic studies show that an electrified system would be beneficial, raising enough money to perform the capital upgrade is a daunting challenge. Private railways would most likely require government assistance or financing from the utilities.
9.4.2 Mainline Infrastructure Compatibility The electrification of a section of existing mainline cannot be undertaken without considering the requirements that the electric locomotives, substations, overhead or third rail power distribution systems and traction return system will place on the existing rail infrastructure. The more significant issues are noted below: §
Tracks may need to be upgraded, including new track work or re-alignment. Sites must be found and real estate acquired for substations. In rights-of-way with restrictive width, the location of the system-wide ductbank requires coordination with track drainage, the foundations for OCS poles and emergency walkways. In all cases, maintenance access must be provided.
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If DC traction is used, the effects of electrolytic corrosion due to leakage (stray) currents must be mitigated.
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Additional clearance may need to be provided in tunnels and at bridges. Existing civil structures may have insufficient clearance to accommodate the proposed electrification system. It may be necessary to lower tracks through overhead crossing bridges. New bridges resulting from grade-crossing elimination will need to be built with adequate electrical clearance. Future widening of existing overhead bridges must be considered.
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Tunnels may be suitable for electrification, or may require costly remedial work, enlargement or “daylighting.”
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Integration of the electrification support structures with existing station canopies must be considered. Station canopies that project over platform edges may need modification.
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Where OCS poles cannot be installed for lack of clearance, attachments, such as wall brackets, will need to be added to civil structures. Pictured at the right is an example of an OCS cantilever attachment to an overhead structure.
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Signals and communication systems will need to be replaced or upgraded. Because electric Figure 9-4 OCS Cantilever Attachment - Courtesy of LTK, Inc. traction systems use the same running rails for traction return current, it is necessary for the two electrical systems to be electrically isolated. The signal circuits need to be “immunized” from the traction power circuits.
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Grounding and bonding of exposed metals is necessary to protect the public from electrical hazards, as well as insuring that there is no interference with the signals and communications systems.
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A central location will be needed to supervise the power system. SCADA, pilot wires or a relaying system must send information to a central point to insure power is being supplied to the system when necessary.
Maintenance More details on these and other aspects impacting the railway route are given later. The advent of electrification increases the level of overall maintenance on the right-ofway. The traction power distribution system, comprising substations, feeder cables, OCS or third rails, lineside disconnect switches, impedance bonds and rail bonds
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urban areas, the structures are often relegated to sidewalks. To help the structures fit into the urban environment, the structures will often serve double duty by acting as light poles, traffic signal poles, etc. On straight or slightly curved track, either cantilevers or cross-spans support the trolley wire such that it is placed over the center of the track. When the track requires tight curves, the trolley wire is held in place with cross-spans, pull-offs and back bones. Although trolley poles pivot at the base, the trolley harp does not pivot so that the trolley wire must be placed towards the center of the curve on sharp curves to allow the trolley shoe to track efficiently. The trolley shoe must be drawn tangentially along the trolley wire, thereby not rubbing against the ‘cheeks’ of the groove. Only by using rigid harps can the trolley shoe diverge onto the correct trolley wire at turnouts, as the pole operates passively being positioned only by the direction of the streetcar on its tracks. Catenary Systems Two-wire systems are referred to as simple catenary and utilize a contact wire and above it, a messenger wire. The messenger wire serves two purposes (1) to support the contact wire vertically between structures by use of hangers and (2) to provide more electrical conductivity. Variations of simple catenary exist, such as low profile simple catenary, which can be considered as a three-quarter- Figure 9-19 Two Cross-span Wires with Full Simple Catenary scale version of the most economic Courtesy of LTK, Inc. simple catenary style. The low profile simple catenary has reduced visual impact by virtue of requiring only one cross-span wire for support between poles compared to the necessary two cross-span wires with full simple catenary as pictured (Figure 9-19). Structure spacing is, however, reduced, thus increasing the pole count by about 30%. Nevertheless, it is still only about half the cost of a single contact wire system with parallel underground feeders, which would be electrically equivalent. Twin contact wires are also commonplace on light rail systems in Europe. Other systems using three conductors called compound catenary are operating, but are more costly and are generally not considered necessary for new installations. Compound catenary utilizes three or more conductors, with a main messenger being the top conductor, the contact wire serving as the bottom conductor, and an auxiliary messenger located between the two. Other styles, which have been installed in the past, include stitched catenary, triangular catenary and ‘hanging beam’ catenary, and all continue in use today.
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Inclined catenary exists to the present day in the Northeastern United States and requires the use of the messenger, and on severe curves, an auxiliary messenger to align the contact wire around curves. This is accomplished by inclining the OCS so that the messenger wire is moved to the outside of the curve while the contact remains close to the track centerline. Sloping hangers support the contact wire at a carefully calculated angle to provide the lateral restraint. Inclined catenary has fixed terminations, which means that the contact wire moves up and down relative to the track surface as temperatures change. Thus greater clearances are required under structures and over grade crossings. Because of the special techniques needed to align inclined catenaries, the trend today is to replace them with chordal (simple) catenary, where the messenger is located directly above the contact wire. Catenary systems are designed to allow the contact wire to operate satisfactorily over the full extent of the carbon-rubbing strip of the pantograph. Careful calculations are performed to determine the extent that the wire can be staggered at the OCS registrations (supports) and to ensure that the pantograph does not dewire in a combination of adverse operating conditions, including strong winds, maximum vehicle sway and poor quality track. These calculations are then used to determine how much the contact wire can be allowed to be placed off the centerline of the track and still allow safe operations. On tangent tracks, the wire is intentionally staggered from one side of the track centerline to the other at successive poles to prevent grooves from forming in the middle of the pantograph carbons.
Figure 9-20 Contact Wire Placement in a Curve - Courtesy of LTK, Inc.
All overhead contact systems exhibit the characteristic of increased sag between supports and loss of tension when conductor temperatures rise due to solar gain and/or current heating. Although small variations to sag and tension do not adversely affect current collection, also called ‘commutation,’ large variations, say over 6 inches, can be unacceptable. In order to control conductor sag between supports, two options are available: §
Limit span length (length between poles)
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Tension compensation (described later)
Both options apply to Single Contact Wire (SCW) systems and to multiple conductor catenary systems to be described later.
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9.8 Electrification Interfaces with Other Rail Elements When an established railway is to be electrified, there can be significant engineering and operational impacts on the existing infrastructure. The more significant impacts involve: §
Right-of-Way
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Track Structure
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Civil Structures
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Signaling and Communications
9.8.1 Right-of-Way Track Layout/Realignment It is desirable that track alignment and modifications to track crossovers and turnouts be completed before route electrification occurs. Additionally, track renewals and track lowering measures, as described below, should have been finished. Future track improvements may need to be accelerated to avoid the need for later changes. Old redundant track should be removed before initiating electrification so that cranes are not impeded by the presence of high voltage catenary wires, conductor rails or cables. Substations Typically, 25kV substations require a site area of about an acre in size, with road access suitable for trucks delivering the largest piece of substation equipment. DC substations are smaller, ranging in size from 2000 to 5000 square feet, but are generally more numerous than AC substations. Supporting Structures for the Contact System On existing main line routes, particularly those with more than two tracks, there will probably not be enough room between tracks to install OCS pole foundations. Therefore, the poles will be allocated to the outside of the line. The right-of-way needs to be examined to insure that structures and any supporting back guys fall within the
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ROW without impeding drainage. Since third rail is attached to the end of the ties, ROW limits are not as critical for third rail systems as for overhead systems. Systemwide Ductbanks Ductbanks are required for power distribution cables and should be designed to accommodate new signal or communication cables, should existing aerial signal and communication cables need replacement. The location of parallel track and cross-track ductbanks will need to be coordinated with drainage pipes, foundations for signals and OCS poles, and emergency walkways.
9.8.2 Track Structure On rail lines, the area extending from track centerline in which no wayside items can be placed is known as the structure clearance envelope. On non-electrified lines, this envelope is based on the dynamic envelope of the vehicle along with passing clearances. For electrified lines, this envelope has to be increased to allow for the electrical clearance envelope. This increased envelope insures that no wayside structures come close enough to any “live” part of the vehicle to create an electrical hazard. One way to provide the requisite vertical clearance at overhead bridges is to lower the tracks. However, if significant lowering is required, the track subbase may need to be excavated first, which may be a prohibitive operating precondition.
Figure 9-23 Clearance Envelope - Courtesy of LTK, Inc.
Because the running rails will be carrying the high currents of the traction return system, it is necessary that all bolted rail joints be paralleled with traction bonding cables to carry the 1000 amps or more of traction current. Defective bonds can give rise to severe arcing between the rails and cause enough damage to curtail normal train operations. The possible effects of electrolytic corrosion due to leakage (stray) currents from the track rails, especially with DC power must be addressed. With AC systems, the effects of leakage currents is considered to be minimal, but still needs to be checked. Leakage currents can cause and/or accelerate corrosion in underground piping, steel reinforcement in concrete structures and may damage underground utilities.
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Passenger, Transit & High Speed Rail INTRODUCTION TO PASSENGER RAILWAY INFRASTRUCTURE “Form ……follows function” Louis Henri Sullivan, Architect, “Lippincott’s Magazine,” March 1896
10.1 Introduction
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he above quotation, while originally written to describe the practice of architecture, nonetheless provides useful insight into the practice of passenger railway engineering. In particular, the concept concisely describes how fundamental differences in design can arise between a railway built for passenger service and one built for freight, as their functions (and hence their forms) may be radically different. However, while a passenger line and a freight-only line may look very different, the same engineering principles apply to each -- sound railway engineering is still sound railway engineering. The applications of these basic engineering principles will vary, however, to reflect the different functions each type of infrastructure must support. This chapter presents an introduction to passenger rail infrastructure requirements. It does not dwell on basic railway engineering concepts. Instead, it expands upon the materials presented elsewhere in this Practical Guide as necessary to provide an overview of typical design principles, construction practices and maintenance considerations applied to passenger rail lines. The emphasis here is on the typical. The authors’
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acknowledge that North American passenger experience is rich with exceptions to the “typical,” and while a few exceptions have been noted herein, no attempt has been made to include them all. Instead, the intent is to provide a basic understanding of typical North American practice. Those interested in learning more are invited to review Chapter 12 (Rail Transit) and Chapter 17 (High Speed Rail Systems) of AREMA’s Manual for Railway Engineering. The reader is also referred to the Track Design Handbook for Light Rail Transit, published by the Transportation Research Board.
10.2 Passenger Rail Modes Passenger rail operations in North America serve a wide variety of functions, from long distance intercity travel to daily commuter trips to local urban transit services. These operations encompass a diversity of vehicle types, operating speeds, right-of-way requirements and service frequencies. The characteristics of each type of operation are so different from one another that it is useful to think of each as a separate rail-based transport mode. For purposes of this chapter, the various types of passenger rail operations will be divided into six categories:
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High-Speed Rail (“HSR”)
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Intercity
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Commuter Rail
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Rapid Transit (“RT”)
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Light Rail Transit (“LRT”)
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Streetcar and Vintage Trolley (“Streetcar”)
These terms will be utilized throughout the chapter in describing the various rail modes and their infrastructure characteristics. People mover operations (such as found in airport terminals) are not addressed here, as these typically use proprietary vehicle and systems technologies, and are often based on rubber tire/concrete paving guideway systems.
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10.3 Distinctions between Railway Operations and Transit Operations The types of operations noted above can be separated into two major subgroups. High Speed Rail, Intercity and Commuter Rail may be considered “railway” operations while Rapid Transit, LRT and Streetcar may be considered “transit” operations. Characteristics, which distinguish between railway operations and transit operations, are discussed in general terms below. Passenger railway operations are conducted over portions of the North American freight rail network, or on dedicated passenger lines that are contiguous to this network and which share compatible technical standards. (In the United States, Part 213.1 of the FRA regulations defines this as the “general system of railway transportation.”) These systems generally utilize AREMA (or AREMA-compatible) technical standards for trackwork and AAR (or AAR-compatible) technical standards for vehicles. As such, these systems represent passenger adaptations of North American freight railway practice, and inter-operability with the freight network is maintained. Intercity and Commuter services are generally compatible with freight infrastructure practice, while HSR will employ more stringent standards for dedicated high-speed territories while retaining compatibility with freight infrastructure for conventional speed operations. Transit operations are conducted on trackage that is dedicated to passenger service, not open to freight operations, and not part of the “general system of transportation.” Technical standards are not based on interoperability with the North American rail network, but rather the stand-alone requirements of each operator. Trackwork and vehicle standards may be AREMA- and AAR-based, but more typically reflect transit practice with use of sharper track curvature and specialized track appliances, and lightweight vehicles with narrower wheels and smaller flanges. For the “traditional” systems (those built in the late 19th and early 20th centuries), track and wheel practice may still reflect the standards in effect at the time of construction. “New start” LRT systems (those built after approximately 1975) may utilize European transit track and wheel practices. There is one hybrid type of operation that should be noted – LRT and freight services operating on shared trackage. In these systems, LRT and freight operations are typically “time separated,” with LRT running during the day and freight running at night. Each service has exclusive use of the system during its designated operating period. In these systems, LRVs utilize wheel standards compatible with standard railway trackwork. Examples of such operations include San Diego and Baltimore.
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Curve Maintenance: The sharp curves found on transit properties can create the need for significant maintenance work. This work can involve gauging, fastener tightening and rail replacement. It is typically done with small equipment adapted to working in close confines.
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Special Track Appliances: As noted previously, transit properties make use of unique turnout designs, extensive check rail installations and other track features, which require maintenance. As these appliances typically require close control of dimensions (such as guard faces and back-to-back distances), significant attention is needed to keep them in adjustment.
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Maintenance Access: Physical access to conduct maintenance can be difficult, particularly for elevated structures and tunnels. Work processes and machinery must be adapted to deal with the available access and working space.
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On some properties, alignment imperfections in small bore tunnels caused by construction tolerances translate to deliberate imperfections in track geometry necessary to keep track centered within the tunnel.
10.10 Special Topics Associated with Passenger Railway Operations 10.10.1 Passenger Railway Line Capacity Unlike highways, which measure unlinked trips over individual route segments, rail line capacity fundamentally must be considered as a network evaluation. The type of train service, where it begins, and where it is destined are equally important components, along with the infrastructure itself. Whether it is through or local operations, routine maintenance or seasonal impacts, operators must consider events that have the potential for creating cascading effects on a given route’s performance, even though they may happen many miles away. Capacity analysis begins with an evaluation of the physical route. The length of the line, terrain it operates through (curvature, gradient, etc.), number of tracks and type of train control exercised over the line all set the stage for determining some of the most basic components of line capacity. Train performance characteristics in terms of maximum speeds, acceleration (HP/ton) and deceleration rates are critical to determining throughput rates for unopposed trains. Equally as critical is the mix of
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train types, as there will be pronounced differences in end-point transit times when comparing passenger, intermodal, manifest and unit freight train types. Distance between terminals, capacities of the terminals, local switching enroute, performance variability and day-of-week variability are key factors to be considered. Where passenger trains operate over a freight route, the difference in running times becomes even sharper. Besides the criteria typically considered for freight service, the number of station stops, dwell times at each station, and distances between stations must be considered. Passenger trains typically are permitted to operate at higher maximum speeds and through curves at higher speeds by employing greater levels of cant deficiency when compared to freight trains. The effect of both is to further reduce transit times. Terminal operations must also be factored into a line capacity analysis, as trains typically follow a different route or multiple routes at slower overall speeds compared to operations on the main line. If every train operated in the same direction, at precisely the same speed and assuming a relatively sophisticated method of controlling train movements, line capacity over a single track would be very high. If this same group of trains were split evenly so one half operated in the opposite direction and uniform length passing sidings were evenly distributed, line capacity would drop proportionate to siding distance and to reflect the time required to reset routes through interlockings and for trains to accelerate and decelerate for siding entry and exit. Overall capacity would remain relatively high, however. Neither of the above situations occurs often in real life. Geography, community development, and the markets served can, and do, greatly affect the design and configuration of a rail line. Much more typical would be sidings of varying lengths, with unequal distances between them. Ruling grades frequently bring average speeds of freight trains down to very slow speeds or require adding helper locomotives to negotiate grades. Dispatchers must carefully plan meets between opposing trains of varying types around the physical infrastructure capable of accommodating them. Intermodal and passenger trains will “overtake” slower trains along the route and dispatchers must stage passes between trains running in the same direction in order to allow the faster trains to proceed without delay. Locals and work trains occupy main line tracks for extended periods of time while performing their duties. The net effect of all of these operations is to reduce rail line capacity. Rail line capacity is not easily determined. In addition to differences in the types and numbers of trains, their speeds and their overall reliability, capacity is constrained by the number of tracks, interlockings and their spacing, types of train control and signal systems in place, FRA track class, moveable bridges, permanent slow orders, grade crossings, etc. Each of these elements may contribute to, or reduce, the handling capability of a route.
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Undertaking an operations simulation of the line is one accepted method to determine line capacity. This is generally performed through the development of representative operating plans, for both existing and future scenarios, and testing them against the available fixed plant. Iterative variations of plans can lead to identification of optimal operating plans that maximize use of the line. Most simulations are now performed through use of computer software programs, the more sophisticated of which accurately emulate actual operating conditions. These programs also provide a powerful set of decision-making tools to help determine infrastructure improvements. They may be used to identify chokepoints on a line that constrain growth, to adjust fixed plant investment in response to traffic changes, or to assist in programming maintenance activities. Computer simulation technology continues to advance, reducing set up and evaluation procedures, and making its use progressively more valuable in a quickly changing environment. North American railways already operate among the most efficient rail systems in the world (in terms of ton-miles per route-mile). This status has been achieved by a variety of means to balance fixed-plant investment against operating requirements. As projected rail traffic levels continue to grow, greater use of the existing infrastructure will place ever-higher emphasis on maximizing its use. Understanding and being able to utilize each line’s capacity will be key to success.
10.10.2 The Impact of Superelevation (Or Cant Deficiency and Why It’s Important) Chapter 3 introduced the concept of unbalance or underbalance in operation through horizontal curves. In passenger rail terminology, this same concept is generally referred to as “cant deficiency.” The term is drawn from British and European practice where superelevation is referred to as “cant” and the term “cant deficiency” describes the circumstance where a vehicle operates through a curve with insufficient cant to achieve equilibrium. Superelevation (banking or track cant) is a necessary ingredient for safe and comfortable curve negotiation. Superelevation is used to counteract the effects of centripetal acceleration (centrifugal force) on the vehicle and the occupants. The amount the outer rail is elevated is determined by the sharpness of the curve and the speed the vehicles operate through it. Some definitions are in order: §
Balance Speed: The speed at which the combination of curvature and superelevation exactly balance the centripetal acceleration and the resultant force vector is normal to the track plane.
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orders have followed, for example, the Clean Water Act, Pollution Control Standards Act, etc.36
11.2.1
Wetlands Regulations
Jurisdictional wetlands are part of a classification recognized by government agencies known as “waters of the United States.” The term “waters of the United States” is:
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All waters which are currently used, or were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide;
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All interstate waters including interstate wetlands;
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All other waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes or natural ponds; the use, degradation or destruction of which could affect interstate or foreign commerce including any such waters: i.
Which are or could be used by interstate or foreign travelers for recreational or other purposes; or
ii. From which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or iii. Which are used or could be used for industrial purpose by industries in interstate commerce;
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All impoundments of waters otherwise defined as waters of the United States under the definition;
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Tributaries of waters;
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The territorial seas;
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Wetlands adjacent to waters (as discussed later in this chapter). “adjacent” means bordering, contiguous or neighboring.
The term
The traditional definition of a wetland is the transitional land between the terrestrial and aquatic environment where the water table is usually at or near the surface, or the land is covered by shallow water. Wetlands must have the following attributes: 1) At least periodically, the land supports predominantly hydrophytic vegetation; 36
Jain, R.K., L.V. Urban, G.S. Stacey and H.E. Balbach, 2002, Environmental Assessment, McGraw-Hill, Inc.
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2) The substrate is predominantly undrained hydric soil; and 3) The substrate is nonsoil and is saturated with water or covered by shallow water at some time of the growing season each year.37 Since European settlement began in the United States, millions of acres of wetlands were drained, dredged or filled so that by the mid-1980’s, almost 53% of the lower 48 states’ wetlands had been eliminated. At that time, an estimated 104 million acres of wetlands remained, which amounts to approximately 5% of the country’s land surface.38 Traditionally, wetlands have been viewed as wild places, teeming with mosquitoes, venomous snakes and disease, while in reality they provide a number of valuable benefits. Some of these include: 1) 2) 3) 4) 5) 6)
Flood storage and conveyance, Groundwater recharge, Erosion reduction and sediment control, Pollution control, Wildlife habitat, Recreation and education.
This listing only highlights a few of the many functions wetlands provide. The Illinois Department of Natural Resources (IDNR) Wetlands Program considers the full range of wetland functions and values when administering its wetland protection responsibilities.39 The United States Army Corps of Engineers (USACE) has been involved in regulating activities in navigable waterways through the granting of permits since the passage of the Rivers and Harbors Act of 1899. This program was meant to prevent obstructions to navigation. By the early 20th century, the USACE had regulatory authority over the dumping of trash and sewage. Passage of the Clean Water Act in 1972 greatly broadened the USACE’s role by giving them authority over dredging and filling in the “waters of the United States,” including many wetlands.40
Chinn, R., 1998, Wetland Delineation and Management Training Manual and References, Richard Chinn Environmental Training, Inc., Pompano Beach, FL. 38 Dahl, T.E., 1990, Wetland losses in the United States 1780s to 1980s, United States Department of the Interior, Fish and Wildlife Service, Washington, DC. 39 Illinois Department of Natural Resources, 2000, A Field Guide to the Wetlands of Illinois, Second Edition, Illinois Department of Natural Resources. 40 U.S. Army Corps of Engineers, Undated, Services for the Public-US Army Corps of Engineers, http://www.usace.army.mil/public.html. 37
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Permit Number 1, Category II, impacts 0.25 to 2 acres of waters of the United States or impacts high-quality aquatic resources. Individual Permits may be required for impacts over 2 acres. Mitigation is required for impacts over 0.25 acres at a minimum of 1.5:1 replacement. In addition, some local regulations may apply. For example, in DuPage County, Illinois, the County regulates all activities in wetlands, and mitigation is required for all impacts. The County’s jurisdiction supercedes the USACE’s jurisdiction. While a USACE permit is still required, if the County’s permit is approved, the USACE’s permit will be approved. USACE Non-Jurisdiction Over Isolated Wetlands On January 9, 2001, the U.S. Supreme Court issued its opinion in the Solid Waste Agency of Northern Cook County (SWANCC) v. U.S. Army Corps of Engineers (USACE). The Court ruled 5-4 against the USACE and EPA and in favor of SWANCC, overturning the USACE’s requirement for a Clean Water Act Section 404 permit for the construction of a landfill involving the fill of isolated wetlands at a former gravel mining site.46 As a result, the primary effect of the decision is that the Migratory Bird Rule, under which the USACE asserted jurisdiction over isolated wetland areas, non-navigable and completely intrastate waters based solely on the presence or potential presence of migratory birds, is no longer valid. Therefore, isolated wetlands are no longer jurisdictional to the USACE. All tributaries to Waters of the United States (such as interstate waters, tidal waters, etc.) as well as wetlands contiguous to and adjacent to those tributaries are still regulated. To be contiguous or tributary, there must be a continuous surface water connection between the two aquatic areas. This surface water connection can be either surface flowing water at regular intervals of time, or a continuum of wetlands between the two areas. Groundwater, surface overflow of extreme precipitation events, or tiling do not constitute surface water connections. A culvert under a road fill connecting two aquatic areas would constitute a surface water connection, provided the culvert is not excessively long. Excessively long piping between two aquatic areas would not constitute a surface water connection. The term “excessively long” is defined on a case-by-case basis by the USACE reviewer. In addition, any natural stream that is placed in a culvert for extended lengths, with waters on each end, would continue to be considered a tributary. States are moving fast to regulate isolated wetlands (non-jurisdictional to the USACE). For example, recently Lake County, Illinois has adopted an ordinance, which regulates all wetland areas that are not regulated by the USACE. If a wetland is identified on the site and is considered isolated, a permit by the USACE is not required, however, a Lake County Watershed Development Permit is required.
Miller, Z.C. and C. Kamper, 2001, Memorandum, Regarding Supreme Court Decision in SWANCC, http//www.dgslaw.com/articles/347951.html.
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11.2.4 Best Management Practices Best Management Practices (BMPs) are policies, practices, procedures or structures implemented to mitigate the direct and indirect degradation of surface water quality from an activity. BMP’s are required for all permits, to the extent possible. BMPs include non-structural elements, such as the preservation of existing natural areas (floodplains, streams, wetlands, prairies, woodlands and native soils) and drainageways, and structural elements. Structural elements include vegetated swales, filter strips and infiltration trenches, which are designed to remove pollutants, reduce runoff rates and velocity, and protect aquatic resources. Another BMP is to limit the amount of impervious surface area through practices such as reducing road widths and clustering developments designed around open space. In addition, a project should use the following structural BMPs, if appropriate, both individual lots and the overall site to the maximum extent practicable: 1) Lot controls: grassed swales, underground sand filter, infiltration trenches, vegetated filter strips, vegetated natural buffers, level spreaders, dry wells or roof downspout systems, rubber rooftops. 2) Site controls: wetland detention, wet bottom detention, grass swales, infiltration basins, vegetated swales, vegetated natural buffers, level spreaders, curb cuts, leaky berms. Applicants who protect water quality and minimize run-off by designing and implementing a comprehensive and coordinated use of BMPs throughout the project site may receive partial compensatory wetland mitigation credit. For additional BMP’s, please refer to the Illinois Urban Manual.47
11.2.5 Endangered Species Section 10 of the Endangered Species Act is designated to regulate a wide range of activities affecting plants and animals designated as endangered or threatened, and the habitats upon which they depend. The Act prohibits many activities affecting these protected species unless authorized by a permit from the United States Fish and Wildlife Service or the National Marine Fisheries Service. Parts of the Act make it unlawful to take (which includes harm, harass, pursue, hunt, shoot, wound, kill, trap, capture or collect any wildlife within the United States); remove and reduce to possession any plant from areas under Federal jurisdiction; maliciously damage or
U.S. Department of Agriculture, Natural Resource Conservation Service, 1995, Illinois Urban Manual, A Technical Manual Designed for Urban Ecosystem Protection and Enhancement, Illinois Environmental Protection Agency, Springfield, IL.
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destroy an endangered plant on areas under Federal jurisdiction; and remove, cut, dig up, or damage or destroy any endangered plant in knowing violation of any state law or regulation or in the course of a violation of a state criminal trespass law. These prohibitions apply equally to live or dead animals or plants, their progeny (seeds in the case of plants), and parts or products derived from them. An “endangered species” is any animal or plant that is in danger of extinction. A “threatened species” is any animal or plant that is likely to become endangered in the near future. “Critical habitat” is a geographic area which maintains biological/physical features essential to conservation of the species and which may require special management, consideration or protection. A take permit allows for the taking of listed species that may result from a lawful development activity. Take permits are issued by the United States Fish and Wildlife Service and/or the National Marine Fisheries Service. Applying for a take permit requires a completed application form, any necessary supporting materials and an application fee.48 Coordination should occur as early as possible and usually occurs in conjunction with other project permits or authorizations such as Corps of Engineers or Coast Guard Permits, Bureau of Land Management Easements and NPDES (construction) Permits.49 In addition, no activity is authorized under any NWP, which is likely to jeopardize the continued existence of a state or federally listed threatened or endangered species or a species proposed for such designation, as identified under the Federal Endangered Species Act, or which will destroy or adversely modify the critical habitat of such species.
U.S. Fish and Wildlife Service, Undated, Permits for Native Species, Under the Endangered Species Act, U.S. Department of the Interior and the U.S. Fish and Wildlife Service. 49 AREMA Committee 13, 2001, Environmental Permitting Issues on Railroad Construction Projects, Conference Notes, Overland Parks, KS, AREMA, 8201 Corporate Drive, Suite 1125, Landover, MD 207851420. 48
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Native American Graves Protection and Repatriation Act
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Archaeological Resource Protection Act.
In addition, check with local authorities in your area. For example, Illinois has several other acts to protect cultural resources: the Illinois Archaeological and Paleontological Resources Protection Act; the Human Skeletal Remains Protection Act; and the Revised Illinois State Agency Historic Resources Preservation Act. As of 1990, the State Agency Historic Resources Preservation Act requires the same for all private or public undertakings. Some examples of cultural resources are: historic buildings/districts, burial sites, campsites, spiritual sites, churches/cemeteries, trails, tunnels, towers, bridges and miscellaneous structures.
11.2.7 Phase I Environmental Assessment The Phase I Environmental Assessment is an essential first step in determining whether contamination exists on a property. It is important that a Phase I environmental assessment is completed before proceeding with additional site investigation activities. A Phase I Environmental Assessment is a report that includes record reviews, interviews and physical property inspections to identify areas of potential hazardous substance contamination. The following is an example of details that may be included in a Phase I environmental assessment: 1) Property overview: Property information, geographic features and potential receptors/environmentally sensitive areas. 2) Property history: Site specific conditions (past and present): Products (for example, abandoned drums of pesticides, etc.), waste inventory, waste disposal processes and recycling or reuse, bulk storage tanks, chemical and waste storage areas, disposal sites. 3) Regulatory history: Present activities of owner/operator, permits, inspections, hazardous substance/hazardous chemical inventory and regulatory compliance history. 4) Environmental investigations and cleanups: environmental assessments.
Environmental cleanups,
5) Physical reconnaissance: Investigators investigate by conducting interviews and a field reconnaissance, and evaluating current and past site activities.
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European Curve and Turnout Mechanics Railroading is railroading, although the methods that we use to get to the end product may vary significantly. An in-depth understanding of the geometrical relationships that are common to all railway configurations is essential, whether designing, building or maintaining a high-speed passenger line or a 40 mph drag coal line.
12.1 Introduction
T
he purpose of this chapter is to examine mathematically some key components of the track structure, curves and turnouts, but from a European perspective. The European railway, in many ways, is significantly different than the typical railway of North America. High-speed rail plays a very significant role in not only Western Europe, but also in Eastern Europe as well. In Europe, curves are built broad and long, favoring high-speed operations. The approach in North America is entirely different. Privatized North American railways were built to keep construction costs down and to bridge great distances as quickly as possible. This translates into sharp curvature and heavy grades, even for heavy haul activities. The need to move bulk commodities over great distances favored the loading and design approach used by North American railways. The excellent road system developed over the vast majority of the populated segments of North America has relegated the majority of passenger rail travel to a limited few heavily populated corridors. In Europe, the exorbitant cost of fuel, a very high population density within countries the size of states or provinces, along with a nationalized system of railways, has necessitated and enabled the development of an extensive passenger rail based system. Naturally, the European and North American rail networks evolved in two very different directions. The one system is based solely on the reliable movement of heavy
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tonnage at the lowest cost. The other on pure speed. Vehicle and truck/suspension development also took diverging paths between the two continents. European trucks are set much further in than their North American counterparts. Truck (bogey) suspensions handle track anomalies much differently in Europe. Europeans do not stagger joints as is done in North America. Rock-off is unheard of in jointed territory. On the other hand, vehicle bounce can be accentuated. Today though, the North American engineer may need to take a new look at how our counterparts "across the pond" have surmounted the problems of dealing with operating at high speeds within existing alignments. North American railways are looking for ways to operate faster at lower costs. European tangential turnouts have been successfully installed in a number of heavy-haul territories. There is renewed interest in high-speed inter-city passenger trains with a number of feasibility studies underway. A new 110-mph Amtrak/IDOT service between Chicago and Springfield, Illinois will soon initiate service. This chapter does not pretend to cover all the significant design approaches used by European railways in the handling of curvature and turnouts, particularly at high speed. Nor does it present itself as being totally inclusive of European practices. There is wide variance between systems in Western and Eastern Europe. But the reader hopefully will get an appreciation of why Europeans have taken the approach they have to these two topics. In addition, the commonality will also be apparent and hopefully, the reader will secure a better appreciation of why we in North America have developed the standards that we have.
12.2 Curves 12.2.1 Curve Definition Prior to discussing curve engineering, one must have a common method of defining a curve. There are two ways of describing curvature in common practice. In North America, a railway curve is described by the angle in degrees subtended by two radii, whose end points on the curve form a chord of 100 feet in length. In other parts of the railway world, the length of the radius described above, measured in meters, describes the curve. The circumference of a complete circle is 2 ⋅ R ⋅ Π . Since the full body of a curve is theoretically circular in construction, each degree of curvature will describe 100 feet of chord (at relatively small degrees of curvature, the arc distance is approximately equal to the chord distance). Thus, the circumference for such a circle made up of 100 foot chords, each describing 1° of curvature, would for practical purposes, be 3600 feet and the radius would be:
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The maximum permissible rate of elevation increase will vary with different railway companies. The SNCF network permits up to 70mm/sec on the DB (Deutche Bahn) network up to 35mm/sec and on the JNR (Japanese National Railroad) up to 42mm/sec. According to Prof. A. Prud’homme, a rate of elevation increase of 100mm/sec. is theoretically possible for high-speed trains, but is not the practice of the European railways.56 If the rate of elevation increase on the ramp is 28mm/sec, we can get the horizontal component length of the ramp by: l = 10 ⋅ V ⋅ h
The value determined is generally rounded to the nearest 5m or so. For heavy curvature or gradients, the permissible rate of elevation of increase is increased to 35mm/sec. or: l = 8 ⋅V ⋅ h
For high-speed rides, Deutche-Bahn AG recommends: l = 12 ⋅ V ⋅ h
Shock (Jerk) In Europe, a parameter called shock (jerk) is utilized to determine the configuration of the ramp. The magnitude of the vertical jerk is defined as a change in the vertical acceleration within a given time span: Ψ=
da æ m ö ç ÷ dt è s 3 ø
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Professor A. Prud’homme, “General Revue for French Railroad,” November 1976, Paris, France.
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The curved ramp is the second type of ramp configuration used in Europe to transition in superelevation and is shown in Figure 12.7. The slope of this ramp varies along the curve and the greatest slope is located in the middle of the ramp, at point S in Figure 12.6. It follows: 1 : ns =
2h 1000 ⋅ l
Figure 12-6 JZ (Yugoslavian) Superstructure Regulations
The curved ramp (spiral) is longer than the linear ramp and thus, it is more suitable for higher speeds. The curved ramp is used for speeds up to V=180 km/h (112 mph) and its length is defined by: Lcurve = 1.41 ⋅ Lstraight
where Lstraight is the length of the associated linear ramp (i.e., about 41% longer) The greater the rate in acceleration change, the longer the required ramp must be. In the sinusoidal ramps (utilized in the Tokaido Railroad), the length of ramp is calculated by: Lsin = 1.60 ⋅ Lstraight
In the case of the curved ramps, the resultant curve and the slope increase in the form of two squared parabolas touching, but whose slope constantly changes. In the case of sinusoidal ramp, the largest curve is at the beginning and at the end of the ramp, while the vertical velocity is continual. Sinusoidal Ramp Sinusoidal ramps are longer in length than the other forms of transition ramps and allow higher speeds. For V ≤ 180km / h
max .n s = 4V and n s = 400
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12.4.2 Turnout Calculations Conventional European turnout calculations are based on a geometric projection of the length and the relative direction at the points where the connections are made. This method assumes that kinematic forces rather than dynamic forces determine vehicle response.57 To determine the essential equations, one uses one of the projection methods. The open polygon method option is shown on Figure 12-23 and the closed polygon method is shown on Figure 12-24. Elements of the turnout are projected on a convenient coordinate system. From the geometric length relations, the equation can be written as: The equation representing the open polygon of Figure 12-23 is: A ′E ′ = a ⋅ cos α + b ⋅ cos β + c ⋅ cos γ − d ⋅ cos δ
Figure 12-23 – Courtesy of University of Zagreb
Figure 12-24 – Courtesy of University of Zagreb
The equations representing the closed polygon in Figure 12-24 are: a ⋅ cos α − b ⋅ cos β − c ⋅ cos γ = 0 a ⋅ sin α + b ⋅ sin β − c ⋅ sin γ = 0
On the European Railway network, the tangent of an angle rounded off to the nearest degree expresses the diverging angle.
Mejgyeri, J., Geometric Movement in Turnout Development, Austrian Railway Archive Volume 40, Pages 59–65, 1985.
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For example:
(
)
(
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1 : n = 1 : 10 ∴ α = 50 42'38" or 1 : n = 1 : 14 ∴ α = 4005'08"
The maximum permissible lateral acceleration is 0.8m/sec2. Thus, one could develop a curve in the closure rail with a radius that, for a desired diverging speed, generated a lateral acceleration of a = V2/R, not exceeding 0.8m/sec2. This curve would be independent of the frog number utilized. In effect, Europeans will utilize a variety of turnout closure rail curves with the same movable point frog in order to secure different diverging speeds. The resultant turnout, obviously lengthens significantly as the radius of the curve grows. This is in direct opposition to the turnout practices of North American railways, that utilize one given closure rail curve for a given turnout number. The effective radius is performed by calculating the offset at the switch heel, based on a chord (12.2m or 40’) centered about the switch heel. The calculated offset will provide the effective radius ( R ) at the switch heel by using:
C2 R= 8 ⋅V On the JZ (Jugoslavian Railroad), the chord length of 12.2m is the shortest distance between wheel set centers (truck centers currently in service). Thus, for example, in high-speed operations, the diverging angle can be:
α = 2°29'22"∴ (tan α = 1 : 23.5) and the permissible diverging radius is R=1390m (4,560 ft.). This permits a diverging speed of 80 km/h in 120 km/H territory. For 100km/h in a diverging route, we need a curve with a radius of 1500m. As determined by the following equation: Vmax = 2.91 R1/2 This radius is coupled with a tan α = 1:18.5 or diverging angle α = 3º05’38.4”. For Turnout Model EW (1:40.154) (DB Railroad), α=1º12’ 7.5” (tan α=1:40.154) with a radius of 6100m (20,013 ft), which allows a diverging speed of 200 km/h.
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#1 – Casky, KY – Project Survey
Project Summary
Location • Casky, Christian County, Kentucky Description • Construct new mainline in order to create new 5,600 TF stub ended industrial lead track. Railroad(s) involved • CSX Transportation, Inc. Construction Cost • $1.47 Million
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Construction Duration • Proposed - Spring 2001 to Fall 2001 • Actual – Summer 2001 to Spring 2002 Statement of Need
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The traffic flow along this corridor is high density and high speed. Switching industries off the main track has caused transportation delays for through trains and impacted switching operations for five industries. In addition, future industrial growth in this area is suspended. This location is the fastest growing industrial area for the CSXT. Five industries were installed in the last five years. The benefits gained from the new construction will allow CSX to increase velocity of trains operating in this corridor and increase the opportunity for future growth in the Hopkinsville Industrial Park.
Project Understanding (Definition)
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A new main track, west of the existing line, will be constructed. The old main track will be used as an industrial lead with access on the south end only. Industrial Development gains the opportunity to grow the business on the north side by future extension of the industrial lead. When fully developed, this industrial lead will connect to the south end of “Casky Siding,” providing CSX with a 20,000 foot siding when the industrial lead is not in use. The rate of return is 18% for $1.47 Million
• Identify Stakeholders Railroad
Train Operations •
CSX Transportation, Inc.
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Train Operations, Design & Construction, Industrial Development, M/W, Train Control, Real Property, Inc. and Outside Railroad Contractors (Design, Grading and Track) were main players from the railroads approach to the project.
Planning Department
(Critical Dependencies)
Train Operations/Industrial Development Dept. •
Defined project scope and provided funding for construction.
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Design and Construction performed preliminary design, prepared estimate for the track, performed project inspections, managed budget expenditures, employed track and grading contractors, monitored construction progress, ordered track materials, coordinated curfews & track time and coordinated with the County for local road closing.
Design & Construction
Engineering Department • •
MOW – performed track inspections, scheduled work trains and provided track protection for the project. Train Control – performed all work associated with signals.
Real Estate Department •
Real estate group researched property issues and negotiated price sales with local landowners. In addition, handled deed records for new acquisitions.
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Design Contractor •
Provided detailed design engineering and construction quantities.
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Constructed roadbed in accordance with CSX specifications.
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Constructed all track and performed track shifts in accordance with CSX specifications.
Identify Stakeholders
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Non-Railroad
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(Critical Dependencies)
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Christian County – the county transportation officials reviewed road crossing approach design and helped coordinate road crossing closing. Advance warning signal protection remained flashing lights only. WorldCom – fiber optic company relocated fiber optic cable outside project limits to allow the start of construction. 5 Industries – Sun Chemical Corp., Budd Talent Co., Seimer Milling, Continental Mills, and Free Flow Pkg. gain better switching operations. Coordination with Sun Chemical to relocate switch out of mainline and install in new industrial lead. Track was out of service for 1 week.
Grading Contractor Track Contractor
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Feasibility Assessment
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Construct new main line on west side of existing main track and realign existing main track, at each end, into the new main. Will need to purchase property from adjoining property owners in order obtain enough area to build roadbed in accordance to CSX specifications.
Alternative Analysis
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Build new industrial lead track on east side and relocate all industrial switches out of the main and into the new lead track. Will need to construct roadbed and realign all industrial tracks for 5 industries. No new property needed, right of way is sufficient to support roadbed according to CSX specifications. Rejected this alternative because all 5 industrial tracks would require substandard curvature.
Design
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All construction according to CSX specifications. Roadway materials to be built in accordance with KYTC specifications. Maximum degree of curvature for industrial tracks is 12 degrees. (Should never exceed 17 degrees) All railroad construction is to not interfere with the wetland area. All track work and grading work to be performed by outside contractors.
Operating Criteria
• • •
Time table speed to remain at 60 mph for this segment of track with temporary slow orders as the work was in process. Curfew times would only be available on Mondays and not to exceed 8 hours. Maximum allowable track time for any other day would not exceed 4 hours. Road crossing could be closed for a period of 1 week.
Project Management
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Key Project Elements
Overall project management falls with the Project Engineer from Design & Construction. The Roadmaster will schedule track protection during the work and schedule work trains to dump ballast. In addition, the Roadmaster will provide final inspection of the track construction. Train Control will be responsible with progressing along with the track construction and manage all signal-related issues.
Operating Parameters
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The railroad operates approximately 40-45 trains per 24-hour period. Mondays generally have one scheduled critical train, UPS, which runs during morning hours.
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Schedule
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Critical Design Considerations
Project to start early Spring 2001 and be completed prior to Thanksgiving, due to UPS peak season. In addition, asphalt plants close in early November.
Property Acquisition
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Need to acquire two adjoining parcels of land in order to construct roadbed according to CSX specifications.
Utility Service Availability
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Utility service for crossing protection and industrial switch is not an issue. The 5 industrial switches are dispatch controlled and already have electrical service. Industrial lead switch required one pole drop and power was fed by a nearby electrical line.
Grade-Crossing Considerations
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Asphalt approaches for new road crossing shall fall off at a minimum of 1%, for a distance of 28 feet from the outside edge of rail. Extending further away, approaches can fall off no greater than 8% until it ties into the existing road.
Construction Phasing
Project Challenges
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Grading construction will start after fiber optic cable has been relocated. Train Control will install buried signal wire in roadbed prior to subballast installation. Track contractor will start track work after subballast is installed and all material delivered. Train Control will work along with track contractor schedule in order to keep signal protection for the railroad. Track and Grading contractors will coordinate road crossing installation in order to minimize road crossing closure time.
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Complete project prior to CSX-UPS peak season, which begins November 23rd and ends December 25th. Start grading work prior to having all property acquisitions under contract. In addition, Fiber Optic company was waiting on final property lines to determine which side of track to relocate fiber optic cable. Completing grading work within 45 days was not attainable. Contractor experienced 20 days of weather related delays. Redirect waterway for pipe outlet after grading contractor built pond for local property owner. Waterway originally exited into wetland/tree line area. Local property owner, as part of his construction contract with grading contractor, instructed the contractor to build a pond near the CSX property line and direct all ditch lines to the north to empty into pond. The pond elevation was higher than outlet end of pipe, causing water to pond up in water channel and soak into roadbed. CSX had grading contractor to close south water channel to pond and redirect waterway for the pipe in opposite
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direction. Providing a location to spot 8 ribbons of rail prior to grading work being completed. Finding a staging area to receive and distribute track material onto roadbed. Track contractor did not have same construction easement with local property owner. Dump ballast on the new main and surfacing the track prior to the track shifts. Project had limited access and trucking in ballast was not an option. Our original proposal was to construct the industrial lead up to the first track shift location on the south end, then shift the main on to the industrial lead and run trains through the industrial lead switch for 3 days. This meant that this section of corridor would operate without signals for 3 days. A week prior to cutover, Transportation rescinded their original plan of approval. We then decided to install a temporary turnout on the north end in order to dump ballast and surface track. Track shifts on the north and south ends would both occur during the same curfew.
Need property acquisition to occur prior to construction season starting. Property acquisitions for project caused 2 months delay, preventing the Grading Contractor from starting in April. Provide language in construction contract where Contractor will be penalized for not meeting the construction schedule. Granted, 20 days of delay was attributed to weather delays but other outside interferences caused additional delays.
Be firm with outside contractors. Remember that contractors are working for you. In addition, cover the general conditions during the pre-bid meetings and after the contract has been awarded. Contractors sometimes forget their responsibilities and play stupid when told of them. Instruct Contractors to complete a daily progress report and provide this to you on a daily/weekly basis. This will allow you to keep up with days worked, activities performed on each day and can be used as a tool for future references. Preach the importance of Safety from the pre-bid meeting up until the contractor completes the job. Watch the finances from the beginning and complete budget forecasting every few weeks to determine if project is on budget.
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STRINGLINING OF RAILROAD CURVES 1995 ROADMASTERS & MAINTENANCE OF WAY ASSOCIATION COMMITTEE REPORT Chairman: A.M. Charrow, Asst. Dir. - Mtce., Santa Fe Co-chairman: B. Jamison, Tech. Instr., Norfolk Southern
In this age of automatic tampers, computers, geometry cars and, of course, reduced forces, why bother teaching the traditional methods of stringlining? The answer to that question is that the traditional methods of stringlining will allow the practitioner to rapidly field determine curvature and, if necessary, line track with low-tech hardware. Railroad track is a dynamic structure, and there are many causes of its movement from design alignment to one of irregular alignment, particularly on curves. Train operations impart forces to the track structure, which, over time, tend to change the alignment. Our predecessors who discovered that as speeds increased, the alignment entering and leaving simple curves became distorted recognized this early, which in turn lead to the development of transition curves between the tangents and simple curves and spirals. However, even with perfectly designed curves with the correct superelevation and spiral length for the associated curvature and track speed, lateral forces will still occur as not every train will be operating at design speed. Running traffic at an unbalanced condition is a compensation for this, but lateral forces will still be imparted to the track related to directional tonnage, grades and current of traffic operation. Therefore, alignment should be expected to change or deteriorate as time goes by through normal operations, eventually requiring surfacing and lining. Compounding the above, there exist locations not blessed with perfectly designed or constructed subgrades, which for various reasons, poor original location, poorly constructed fill, slides or high water, the alignment changes. Another type of track instability relates to thermal expansion and contraction, primarily the dreaded sun-kink, which can make the alignment most irregular, possibly leading to catastrophic results. Less dramatic changes in alignment will occur also, as I am sure most of you have seen curves gradually shift in and out during the different seasons, especially where insufficient ballast exists. Another cause of irregular curve alignment, or at least alignment different from what was originally designed, is previous lining. Years of smoothing and surfacing without staking will result in a curve that while perhaps not particularly bad looking or poor riding might be off alignment. Likewise, normal maintenance operations, such as tie
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GLOSSARY GENERAL RAILWAY DEFINITIONS AND COMMON RAILWAY TERMS “A” End: In a railway freight car, the end that does not have the brake handle; opposite to the “B” end – SEE “B” End.
A
AAR: See Association of American Railroads Adjacent Track: In relation to excepted track and for the purposes of the Track Safety Standards, any track or tracks next to a track that is designated as an excepted track. Any tracks or tracks with centerlines that are 30 feet or closer to the excepted track in question are considered as adjacent and speeds on those tracks must not exceed 10 m.p.h. Adjustment, Rail: A process whereby the neutral temperature of continuous welded rail (CWR) is raised or lowered through the removing or adding of rail. Administrator: The chief officer of the Federal Railroad Administration. That person has the authority to issue safety regulations and other emergency directives. Advanced Signal: A fixed signal used in connection with one or more signals to govern the approach of a train or engine to such signal. Advanced Train Control System: (ATCS) Term referring to the next generation of train control. Aspects of control include accurate train location, train and locomotive monitoring and reporting, computerized analysis and track orders, and automatic order enforcement. Adzing Machine: Portable power-operated machine designed to adz (smooth) the rail seat on ties to provide proper bearing for rail or tie plates. AEI: See Automatic Equipment Identification System
Air Dump Car: Hopper Car with air dumping capabilities. Alinement [or alignment]: The position of the track or rail in the horizontal plane expressed as tangent or curve. Angle Cock: An appliance used for the purpose of opening or closing brake pipe on ends of cars, rear ends of tenders, and front ends of switch engines so equipped. Provision is made for the supporting hose at proper angle. Antisplitting Iron: A piece of steel strip, beveled on both sides at one edge, and bent to a desired shape, for application by driving into the end (cross section) of a tie or timber to control its splitting. Approach Track: In signaling, the section of track on the approach side of a signal which is equipped with a circuit to detect the arrival of a train and transmit its presence to the controlling circuits of the signal and its associated route. Used to lock a route and prevent it from being altered once a train has approached within a safe braking distance, known as approach control. This prevents the route being changed at a time when the train could run onto it and be derailed. Also use to clear signals normally maintained at danger until a train has approached within a given distance. This distance is calculated to ensure the locomotive engineer sees a red signal as he approaches. This has the effect of causing the locomotive engineer to reduce train speed to a required level, at which point the signal will clear.
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Unbalanced: The superelevation in a curve that is less than a calculated value that will otherwise equally distribute onto both rails the dynamic force of trains that are traveling at the maximum authorized speed.
territorial seas, and (6) wetlands adjacent to waters. Warp: See Difference-in-cross-level Welded Rail: Two or more rails welded together.
Unbalance Speed: Traveling through a curve faster than balance speed. This may also be expressed as the curve being under elevated for the speed. The amount of reduction in elevation from balanced can be as much as 3 inches for conventional equipment.
Wetlands: The transitional land between the terrestrial and aquatic environment where the water table is usually at or near the surface, or the land is covered by shallow water.
Undercutter: Production machine that removes the ballast from the track in one continuous operation.
Wheel Impact Load Detector (Wild): A device found in some Hot Box Detectors or as stand alones, which measure excessive wheel impact on rail.
Under balanced: See unbalanced. Uniform Code of Operating Rules: An operating rules book formerly used in the U.S.A. Unit Train: A freight train consisting of carloads of the same commodity moving from origin to one destination, on one day from one shipper to one consignee on one bill of lading. V
V-max: The maximum speed, based on a mathematical formula, permitted on a curve based on the average curvature and average superelevation. Variation (Crosslevel): The change in crosslevel between two points exactly 31 feet apart in a “short spiral.” [see definition of short spiral] W
Waivers: See exemption. Waters of the U.S.: Regulated by the U.S. Army Corps of Engineers and sometimes state and local authorities they include: (1) Waters used for interstate or foreign commerce, (2) all other waters including lakes, rivers, streams, mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa takes, or natural ponds, (3) impoundments, (4) tributaries of waters of the U.S., (5) the
Wig Wag: A reference to the motion of lights on railway, vehicle-crossing signals. Willful Violation: To intentionally circumvent or ignore a regulatory safety requirement. Wing Rail: See “Frog: Wing Rail.” Wing Wheel Riser: See “Frog: Wing Wheel Riser.” Wood Trestle: A wood structure composed of bents supporting stringers, the whole forming a support for loads applied to the stringers through the deck. Work Train: A train engaged in railway maintenance or repair work. Written Authorization: The formal procedure where a person is designated in a document generated by a railroad to conduct certain safety related functions such as track inspection or maintenance of track under traffic conditions. Wye Track: See “Track: Wye.” Y
Yard: A system of tracks within defined limits provided for making up trains, storing cars, and other purposes, over which movements not authorized by time table or by train-order may be made,
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