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1-i Chapter 1âGeneral Introduction Table of Contents CHAPTER 1âGENERAL INTRODUCTION 1-1 1.1 Introduction 1-1 1.1.1 Background 1-1 1.1.2 Purpose and Goals of the Handbook 1-1 1.1.3 The Handbook User 1-2 1.2 What Is Light Rail? 1-4 1.2.1 Background 1-4 1.2.2 Light Rail Defined 1-4 1.2.3 Light Rail as a Spectrum 1-5 1.2.4 Where the Rails and Wheels Meet the Road 1-6 1.2.5 The Regulatory Environment 1-6 1.3 Handbook Organization 1-7 1.4 Units of Measurement 1-8 1.5 The Endmark 1-9
1-1 CHAPTER 1âGENERAL INTRODUCTION 1.1 INTRODUCTION The purpose of this Handbook is to provide those responsible for the design, procurement, construction, maintenance, and operation of light rail transit (LRT) systems an up-to-date guide for the design of light rail track, based on an understanding of the relationship of light rail track and other transit system components. While this Handbookâs title implies that it pertains only to light rail transit, individual principles discussed herein are applicable to a wide spectrum of railway operations ranging from low-speed streetcars operating in city streets up through metro rail and heavy rail transit lines in exclusive grade separated guideways. Some basic principles are universal, and designers of freight and passenger railroad systems will, upon perusal of the Handbook, likely also find chapters and articles of universal interest. The contents of the Handbook were compiled as a result of an investigation of light rail transit systems, a review of literature pertaining to transit and railroad standards and methods, and personal hands-on experience of the authors. Current research also has been a source of valuable data. 1.1.1 Background This second edition of the Track Design Handbook for Light Rail Transit builds upon the first edition, which is also known as TCRP Report 57. TCRP Report 57, published in 2000, was the culmination of the TCRP Project D-6, which was initiated in 1995. TCRP Project D-6 came about because there was seemingly no consistency in the track design used on those North American light rail transit projects that had been initiated in the 1980s and early 1990s. While much research had been conducted in an effort to understand the mechanisms involved in track-rail vehicle interaction and its impact on track design, no widely accepted guidelines existed to specifically aid in the design and maintenance of light rail transit track. Other than the recommended practices of what was then called the American Railway Engineering Association (AREA), there was no up-to-date and commonly accepted resource of track design information to which a North American light rail transit designer could refer. Since AREA was primarily focused on freight railroads and since information on possibly more applicable design practices overseas was difficult to obtain and often unavailable in the English language, many light rail transit projects were designed using a hodgepodge of criteria, drawn from widely disparate sources. Light rail transit designers had little choice other than to rely on practices developed primarily for heavy rail transit and railroad freight operations that are not necessarily well suited for light rail systems. The result was design criteria that were often internally inconsistent. Moreover, many of those projects, once they had been built, had appreciable maintenance issues due to fundamental inconsistencies between their track designs and the vehicles that were using them. TCRP Report 57 altered the field by providing a single source of information, and it was immediately accepted as an authoritative resource. It is upon that foundation that this Second Edition is built. 1.1.2 Purpose and Goals of the Handbook The purpose of this Handbook is to offer a range of design guidelines, not to set a universal standard for an industry that operates in a wide range of environments. The Handbook furnishes
Track Design Handbook for Light Rail Transit, Second Edition 1-2 the reader with current practical guidelines and procedures for the design of the various types of light rail trackâincluding ballasted, direct fixation, and embedded track systemsâand offers choices concerning the many issues that must be resolved during the design process. It discusses the interrelationships among the various disciplines associated with light rail transit engineeringâstructures, traction power, stray current control, noise and vibration control, signaling, and electric traction power. It also describes the impacts of these other disciplines on trackwork and offers the track designer insights into the requisite coordination efforts between all disciplines. A key focus of the Handbook is to differentiate between light rail transit track and those similar, but subtly different, track systems used for freight, commuter, and heavy rail transit operations. These differences present challenges both to light rail track designers and to the designers and manufacturers of light rail vehicles. There will always be some indeterminacy in the engineering mechanics of light rail transit trackwork because the system is dynamic and functions in the real world. LRT track is subject not only to the vagaries of wear and tear but also to the realities of funding for maintenance in a highly politicized environment. Therefore, while perfection can and should be strived forâ particularly during initial construction, when funding is easier to obtainâit can never be achieved. It should also be noted that trackwork for all types of railways traces its heritage back to animal- powered colliery tramways of the late 18th century. The fundamental design principles that were then selected for those then-new ârail roadsâ constrain what is practical to achieve now. Some problems of the rail/wheel interface will likely be forever intractable because of decisions made over two centuries ago. Hence, maintenance-free track for a light rail system is not plausible. 1.1.3 The Handbook User The user of the Handbook assumes all risks and responsibilities for selection, design, and construction to the guidelines recommended herein. No warranties are provided to the user, either expressed or implied. The data and discussions presented herein are for informational purposes only. The reader is assumed to be a degreed civil engineer or similarly qualified individual who is generally familiar with trackwork terminology and experienced in the application of guideline information to design. For that reason, a glossary of terms that would be familiar to a trackwork engineer has not been included herein. Definitions of common trackwork terms are included in the Manual for Railway Engineering, published by the American Railway Engineering & Maintenance- of-Way Association (AREMA). Terms that are unique to light rail transit are defined within the text of the Handbook as they are introduced. Design and construction of light rail transit projects is a multidisciplinary effort. The reader is presumed to be the person on the project who is responsible not only for the design and specification of trackwork hardware, but also for the design of the track alignment. However, LRT projects are not only multidisciplinary, they are interdisciplinary. It is not possible for any one individual to work separately from the other disciplines.
General Introduction 1-3 In the case of the track alignment engineer, he or she will obviously need to work closely with other civil engineers on the project who are responsible for earthworks, drainage, and roadway work and the structural engineers responsible for bridges, walls, and other guideway structures. Less obvious, but just as important, is the need to coordinate with the following other team partners: â¢ The operations planners, so the track alignment is supportive of the operating plan. This is not only with respect to where the tracks go, but also meeting the operating speed objectives and providing crossover tracks and turnback/pocket tracks at requisite locations. â¢ The designers of the overhead contact system (OCS), so as to be certain that a suitable OCS alignment can be created above the track alignment. â¢ The train control system designers, so the track speeds are synchronized with the maximum speeds the signal system can permit. â¢ The vehicle engineers for vital information about the all-critical rail-to-wheel interface as well as any other restrictions, such as minimum possible curve radius or maximum gradient that the vehicle might impose on the design. â¢ The station architects and site planners when setting the locations of the station platforms. â¢ The traffic engineers, so that interface locations between the LRT tracks and public roadways are configured in a manner that facilitates the smooth and safe operation of rail, rubber-tired, and pedestrian traffic. â¢ The yard and shop design team so that a siteâs typically constrained real estate is used in an efficient manner with due recognition of the fact that track geometry is usually the least flexible component of the overall yard design. In the userâs role as trackwork designer, interfaces will again be required with multiple other disciplines, including most of the list above. Trackwork interfaces will include the traction power engineers for negative return connections to the track, structural engineer for interaction between the track and the bridges that support it, signal engineers for train control attachments to the track such as switch machines and insulated joints, highway engineers for the configuration of roads that are either crossed or occupied by the light rail tracks, vehicle engineers for coordination of the crucially important rail/wheel interface, and a host of others. The track engineer needs to understand the role each of those other parties has in the project, the basic principles associated with the facilities or systems that they design, how those details relate to the track, and be able to ask intelligent questions when appropriate. This Handbook is designed to give the track designer the background necessary to do just that. From the above, clearly the track alignment/trackwork engineer occupies a central position on a light rail transit project. Indeed, the track engineer probably interfaces with more people on the project team than anybody except project management! Itâs a crucial and exciting role! Enjoy it!
Track Design Handbook for Light Rail Transit, Second Edition 1-4 1.2 WHAT IS LIGHT RAIL? 1.2.1 Background Light rail transit evolved from streetcar technology. Electric streetcars dominated urban transit in just about every significant American city up through World War II. But once the war was over, âold-fashionedâ trolley lines were converted to bus operation in droves, all in the name of âmodernization.â By 1965, only a handful of legacy streetcar systems still survived. The genesis of the terminology âlight rail transitâ in the United States dates to the late 1960s when planning efforts were underway at what was then called the Urban Mass Transit Administration (todayâs Federal Transit Administration) to procure new vehicles for legacy trolley lines in Boston and San Francisco. The principals working on that program recognized that, because of the wholesale abandonment of streetcar lines in the previous two decades, the words âstreetcarâ and âtrolleyâ had stigmas with likely negative political consequences for the program. Therefore, the term âlight rail vehicleâ was coined, borrowing from British vernacular. 1.2.2 Light Rail Defined Tracks for light rail transit are generally constructed with the same types of materials used to construct âheavy rail,â âcommuter rail,â and railroad freight systems. Also, light rail vehicles may be as massive as transit cars on heavy rail systems. Consequently, the term âlight railâ is somewhat of an oxymoron and often misunderstood. Therefore, for the purposes of this book, it is appropriate to define light rail transit. The American Public Transportation Association (APTA) defines light rail transit as An electric railway system characterized by its ability to operate single or multiple car consists along exclusive rights-of-way at ground level, on aerial structures, in subways or in streets, able to board and discharge passengers at station platforms or at street, track, or car-floor level and normally powered by overhead electrical wires. To expand that definition: â¢ Light rail is a system of electrically propelled passenger vehicles with steel wheels that are propelled along a track constructed with steel rails. â¢ Propulsion power is drawn from an overhead distribution wire by means of a pantograph or other current collector and returned to the electrical substations through the rails. â¢ The tracks and vehicles must be capable of sharing the streets with rubber-tired vehicular traffic and pedestrians. The track system may also be constructed within exclusive rights-of- way. â¢ Vehicles are capable of negotiating curves as sharp as 25 meters [82 feet] and sometimes even sharper, in order to traverse city streets. â¢ Vehicles are not constructed to structural criteria (primarily crashworthiness or âbuff strengthâ) needed to share the track with much heavier railroad commuter and freight equipment.
General Introduction 1-5 1.2.3 Light Rail as a Spectrum While, as noted above, the Handbook is applicable to railway track engineering for a wide spectrum of railway systems, its principal focus is light rail transit. LRT itself is a broad spectrum and ranges from single unit streetcars running in mixed traffic within city streets at speeds as slow as 25 mph [40 km/h] and even lower up through multiple car trains running on a totally exclusive guideway at speeds of 60 mph [100 km/h] or faster. The streetcar lines in New Orleans are representative of the lower end of this spectrum while the Metrolink system in St. Louis is a good example of the upper end. In much of Europe, these two extremes are often called âtramsâ and âmetros.â In Germany, the terms âstrassenbahnâ (âstreet railwayâ) and âstadtbahnâ (âcity railwayâ) are commonly used. The focus of the first edition of this Handbook was more toward the stadtbahn end of the LRT continuum, since they were the prototype for nearly all North American LRT projects during the 1980s and 1990s. However, because of the resurgence of North American streetcar operations during the first decade of the 21st century, it is appropriate for this second edition of the Handbook to provide additional information on the track alignment and trackwork for strassenbahn-type operations. It is important to note how, along any given light rail transit line, one might reasonably include guideway and track elements that are very much like a strassenbahn while a short distance away the routeâs character might radically change into that of a stadtbahn. LRT is a continuum and, within the framework of the operating requirements of a given project, the LRT track designer can incorporate appropriate elements from each of the modeâs extreme characteristics plus just about anything in between. Light rail lines are fairly distinct from metro rail systems (often called âheavy railâ). The latter are always entirely in exclusive rights-of-way, are usually designed to handle long trains of vehicles (6 to 10 cars per train is common) and have a relatively high absolute minimum operating speed along the revenue route (usually 45 mph [72 km/h] or higher). By contrast, LRT trains can operate in shared rights-of-way, very seldom exceed three cars per train, and speeds as low as 10 mph [16 km/h] are tolerated in revenue service track. These differences usually mean that LRT can be constructed at far lower cost than metro rail transit, although the passenger throughput capacity of the latter is also much higher. If there is any one single characteristic that defines âlight rail,â it is likely the ability of the vehicle to operate in mixed traffic in the street when necessary. This draws a line between the St. Louis example above and a light metro rail operation such as SEPTAâs Norristown high speed line. The operational characteristics of each route are virtually the same, but only the St. Louis vehicle could actually operate in the street if necessary. It is a very fine distinction, and, while purists may quibble with some of the finer points of this definition, it will suffice for the purposes of this Handbook. Several rail transit projects have utilized diesel-powered light railcars (also known as âdiesel mechanical unitsâ or âDMUsâ), which do not meet FRA buff strength criteria. Except for the propulsion system, many of these vehicles and the guideways they run upon closely resemble the
Track Design Handbook for Light Rail Transit, Second Edition 1-6 stadtbahn end of the LRT spectrum. The second edition of the Handbook will not attempt to cover all of the nuances of the DMU mode; however much of the information contained in the Handbook will be directly applicable to professionals working on a DMU project. Throughout this volume, the words ârailroadâ and ârailwayâ will appear. By ârailroadâ the authors mean standard gauge rail operations that are part of the general system of railroad transportation. This includes freight railroads and passenger railroads (such as Amtrak and the commuter rail operations in many cities). The word ârailway,â on the other hand, is intended as a broader term that includes all transportation operations that utilize a vehicle guidance system based on the use of flanged steel wheels riding upon steel rails. 1.2.4 Where the Rails and Wheels Meet the Road Arguably, the two most important defining elements of trackwork for light rail systems are the construction of track in streets and the interface between the wheel of the light rail vehicles and the rails. Track in streets requires special consideration, especially with regard to the control of stray electrical current that could cause corrosion. These embedded tracks also need to provide a flangeway that is large enough for the wheels but does not pose a hazard to other users of the street. Light rail vehicle wheels do not necessarily match those used in freight railroad service. Wheel diameters are usually much smaller, and the wheel tread is often much narrower. Light rail wheel flanges are often shorter and have a radically different contour than railroad wheels. These variations require special care in track design, especially in the design of special trackwork such as switches and frogs. The compatibility of the vehicle and track designs is a central issue in the development of a light rail system if both components are to perform to acceptable standards. These issues are discussed at length in this Handbook. While light rail may need to share right-of-way (R/W) with pedestrians and vehicles, the designer should create an exclusive R/W for light rail tracks wherever possible. This will make operation more reliable and maintenance less expensive. Exclusive R/W can also simplify compliance with the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and similar requirements in other countries. 1.2.5 The Regulatory Environment Virtually every aspect of the operation and maintenance of railroads in the United States is closely regulated by the Federal Railroad Administration (FRA) of the U.S. Department of Transportation. However, very few rail transit operations are subject to any level of FRA oversight and regulation. In fact, as of 2010, the U.S. federal government does not exercise any direct oversight of rail transit operations. Instead, through 49 CFR, Part 659, Rail Fixed Guideway Systems: State Safety Oversight, the U.S. government delegates that responsibility to the states. Therefore, Handbook users must familiarize themselves with any applicable regulations in the state where the light rail transit line will be constructed and operate.
General Introduction 1-7 1.3 HANDBOOK ORGANIZATION Chapter 1 (this chapter) provides general introductory information. Chapter 2 elaborates on vehicle design and critical issues pertaining to track and vehicle interface. These topics include wheel/rail profiles, truck steering within restricted curves and primary and secondary suspension systems, and the effect of these parameters on track and operations. Chapter 3 details issues related to light rail track geometry with particular attention to restrictions imposed by alignment characteristics, such as tight radius curvature, severe vertical curves, and steep profile grade lines. Chapter 4 elaborates on the three basic types of track structures: ballasted, direct fixation, and embedded track. The chapter takes the designer through a series of selections pertaining to the track design. The chapter discusses track and wheel gauges, flangeways, rail types, guarded track (restraining rail), and track modulus and provides references to discussions on stray current, noise and vibration, and signal system and traction power requirements in other chapters. Chapter 5 discusses various trackwork components and details. Chapter 6 provides guidelines for the design and selection of various types and sizes of special trackwork. Included are details pertaining to switches, frogs, guard rails, crossings (diamonds), and associated items. Chapter 7 recognizes that virtually all light rail transit systems require bridges or similar structures. Aerial structures are not uncommon. Chapter 7 provides a framework for determining the magnitude of forces generated due to differential thermal expansion between the rail (especially stationary continuous welded rail) and the structure. The analysis elaborates on structural restrictions, fastener elastomer displacement, fastening toe loads, friction and longitudinal restraint, and probable conditions at a rail break on the structure. The analysis includes the conditional forces generated by locating special trackwork on an aerial structure and methods of contending with them. The chapter also addresses the design issues of track slabs constructed on grade, particularly embedded track, since the design principles are distinctly different than ordinary roadway pavement. Chapter 8 stems from the fact that light rail transit uses the running rail as a negative return in the traction power system and highlights the issues pertaining to stray current and discusses the need to electrically insulate the rail and thereby retard the potential for electrical leakage. Methodologies for establishing magnitude, identifying sources, and developing corrective measures are part of this chapter. Chapter 9 introduces the designer to another environmental issue pertaining to light rail transitâ noise and vibration. It explains wheel/rail noise and vibration and the fundamentals of acoustics. It also discusses mitigation procedures and treatments for tangent, curved, and special trackwork.
Track Design Handbook for Light Rail Transit, Second Edition 1-8 Chapter 10 highlights issues related to signals and related train control systems for light rail transit and discusses some of the interfacing issues and components that must be considered by a track designer. Chapter 11 presents elements pertinent to traction power, including supply system and substations, the catenary distribution system, and the power return through the running rails. The chapter also discusses corrosion control measures to mitigate the effects of DC current to adjacent services. Chapter 12 discusses issues related to the application of LRT into a street environment, particularly mixed traffic streetcar-style configurations. Chapter 13 describes considerations the track designer should understand about how the project will actually be built. These include the âmeans and methodsâ of how the track constructor will actually perform the work and how the track construction activity will interact with the construction of other infrastructure and systems. Chapter 14 describes the activities that will be necessary to maintain the track system in a state of good repair so that it can continue to meet the operational goals of the project. Emphasis is given to avoidance of details that either have high maintenance requirements or are difficult or impossible to routinely inspect and maintain. An overall table of contents lists only the 14 chapter topics. Each chapter contains its own detailed table of contents; list of figures and tables; and, in some cases, a reference list. Pages are numbered by chapter (for example, 4-24 is page 24 in Chapter 4). Exhibits within each chapter are assigned a three-digit number indicating the chapter and article in which it appears. For example, Figure 7.3.4 would be the fourth exhibit in Article 7.3 of Chapter 7. 1.4 UNITS OF MEASUREMENT The first edition of the Track Design Handbook (TCRP Report 57), published in 2000, utilized metric (SI) units as the primary system of measurement, with U.S. traditional units following [in brackets]. This was in keeping with federally mandated standards at the time TCRP Project D-6 was being performed. Since then, the legal mandate to transition to SI units of measurement has been repealed. The TCRP Project D-14 scope therefore required reversal of the pattern used in TCRP Report 57, i.e., this report uses U.S. traditional units first and SI units second [in brackets]. However, this revised protocol is reversed when the dimension being discussed is metric in origin, particularly in the case of products which are manufactured to SI dimensions. For example, all contemporary light rail vehicles are designed and constructed using SI units. In such cases, the metric version will be listed first, followed by a soft conversion into U.S. traditional units, e.g., 180 mm [7 inches]. In the rare event that an exact translation into U.S. traditional units is required, decimal inches or decimal feet may be employed, e.g., 180 mm [7.087 inches] instead of fractions. Most unit conversions used in the Handbook are âsoftâ and therefore respect the practical tolerances implied by the primary dimension. For example, if a dimension is stated as
General Introduction 1-9 âapproximately one foot,â the conversion to SI is given as 300 millimeters or 30 centimeters rather than an inappropriately exact conversion to 304.8 millimeters. Where formulae are used in the text, versions in both U.S. traditional units and SI units are provided. The authors have attempted to make the two versions of the formulae as consistent as possible so as to illustrate the process while also deriving answers that are generally consistent. In practice, there will be some divergence due to both the coarseness of the dimensional units in each system and the construction tolerances that are practical. For example, while a constructor might strive to place cross ties to 30-inch [762-mm] spacing, it is probable that as-built dimensions will vary plus or minus a half-inch [13 mm] from that dimension. This in no way invalidates the design because actual in-service loadings will always vary from the theoretical. In addition, it would be irrational for a constructor to attempt to place the cross ties precisely 762 millimeters apart or even 762 mm plus or minus 13 mm. If the project was being designed and constructed in SI units, it is likely that the actual specified cross tie spacing would be a value expressed in a unit that is both consistent with reasonably achievable tolerances and practical for field useâsuch as 75 cm plus or minus a centimeter. 1.5 THE ENDMARK A common style feature in publishing is what is known as an âendmark.â An endmark is a symbol, often with some relationship to the text that precedes it, that is placed at the end of an essay, chapter, or article. As its name implies, it means the reader has reached the end of the discussion. For this second edition of the Track Design Handbook for Light Rail Transit, the authors have selected as their endmark a simplified image of 140ER7B girder guard rail. That rail was a standard of the former American Transit Engineering Association (ATEA) and commonly used on North American streetcar lines up until circa-1960 when it became no longer available. The ATEA itself disbanded in the decade following World War II as very nearly all cities in North America abandoned their trolley lines. Regrettably, streetcar trackwork professionals and their knowledge became widely dispersed. Fortunately, they left behind a notable comprehensive library of information on the design of trackwork for electric street railwaysâthe ATEAâs Engineering Manual. This endmark is a silent tribute to the now long-deceased authors of that volume, who in many ways knew far more about these topics than we can even hope to learn.