Chapter “Track Structure Design

Table of Contents

4.1 INTRODUCTION 4-l 4.2 TRACK AND WHEEL GAUGES AND FLANGEWAYS 4-1 4.2 1 Vehicle Truck Factors 4-l 4.2.2 Standard Track and Wheel Gauges 4-2 4.2.2.1 Railroad Gauge Practice 4-2 4.2.2.2 Transit Gauge Practice 4-3 4.2.2.3 Gauge Issues for Joint LRT and Railroad and Mixed Fleet Operations 4-4 4.2.2 4 Gauge Issues for Embedded Track 4-5 4.2.2.5 Non-Standard Track Gauges 4-6 4.2.3 Gauge Measurement Location 4-7 4.2.4 Rail Cant and Wheel Taper-Implications for Track Gauge 4-7 4.2.4.1 Tapered Wheel Tread Rationale 4-7 4 2.4.2 Asymmetrical Rail Grinding 4-8 4.2.4.3 Variation of Rail Cant as a Tool for Enhancing Truck Steering 4-9 4.25 Track Gauge Variation 4-10 4.2.6 Considerations for Determination of Appropriate Gauge 4-l 0 4.2.6.1 Gauge for Tangent Track 4-10 4.2.6.2 Gauge for Curved Track 4-l 0 4.2.7 Fiangeways 4-11 4.2.8 Guarded Curves and Restraining Rails 4-12 4.2.8.1 Curve Double Guarding 4-13 4.2.8.2 Restraining Rail Design 4-13 4.2.9 Gauge Determination Analysis 4-l 3 4.2.9.1 Nytram Plot-Truck-Axle-Wheel Positioning on Track 4-14 4.2.9.2 Filkins-Wharton Flangeway Analysis 4-19 4.2.10 Gauge Implications of Track Construction and Maintenance Tolerances 4-24

4.3 TRACK SUPPORT MODULUS 4-26 4.3.1 Modulus of Elasticity 4-26 4.3.2 Track Modulus of Various Track Types 4-27 4.3.2.1 Ballasted Track 4-27 4.3.2.2 Direct Fixation Track 4-28 4.3.2.3 Embedded Track 4-29 4.3.3 Transition Zone Modulus 4-30 4.3.3.1 Interface Between Track Types 4-30 4.3.3.2 Transition Zone Design Details 4-31 4 3.3.3 Transition Zone Improvements 4-31 4.3.3.3.1 Transition from Direct Fixation Track to Ballasted Track 4-31

4-i Light Rail Track Design Handbook

4.3.3.3.2 Transition from Embedded Track to Ballasted Track 4-31 4.3.3.3.3 Design Recommendation 4-33

4.4 BALLASTED TRACK 4-33 4.4.1 Ballasted Track Defined 4-33 4.4.2 Ballasted Track Criteria 4-34 4 4.2.1 Ballasted Track Rail Section and Track Gauge 4-34 4.4.2.2 Ballasted Track with Restraining Rail 4-34 4.4.2.3 Ballasted Track Fastening 4-34 4.4.3 Ballasted Track Structure Types 4-34 4.4 3.1 Ballasted Track Resilience 4-35 4.4.3.2 Timber Crosstie Ballasted Track 4-35 4.4.3.2.1 Timber Crosstie Fastening 4-36 4.4.3.2 2 Timber Crossties 4-37 4.4.3.3 Concrete Crosstie Ballasted Track 4-37 4.4.3.3 1 Concrete Crosstie Fastening 4-37 4.4.3 3.2 Concrete Crossties 4-39 4.4 4 Crosstie Spacing 4-39 4.4.4.1 Crosstie Spacing-Tangent/ Curved Track 440 4.4.5 Special Trackwork Switch Ties 4-41 4.451 Timber Switch Ties 4-41 4.4.5.2 Concrete Switch Ties 4-42 4.4.6 Ballast and Subballast 4-42 4.4.6.1 Ballast Depth 4-43 4.4.6.2 Ballast Width 4-43 4.4.6.3 Subballast Depth and Width 4-43 4.4.6.4 Subgrade 4-44 4.4.7 Ballasted Track Drainage 4-44 ’ 4.4.8 Stray Current Protection Requirements 4-44 4.4.9 Ballasted Special Trackwork 4-45 4.4.10 Noise and Vibration 4-45 4.4.11 Transit Signal Work 4-45 4.4.12 Traction Power 4-46 4.4.13 Grade Crossings 4-46

4.5 DIRECT FIXATION TRACK (BALLASTLESS OPEN TRACK) 446 4.5.1 Direct Fixation Track Defined 4-46 4.5.2 Direct Fixation Track Criteria 4-47 4.5.2.1 Direct Fixation Track Rail Section and Track Gauge 4-47 4.5.2.2 Direct Fixation Track with Restraining Rail 4-47 4.5.2.3 Direct Fixation Track Fastener 4-47 4.5.2.4 Track Modulus 4-47 4.5.3 Direct Fixation Track Structure Types 4-47 4.5.3.1 Cementitious Grout Pads 4-48 453.1 .I Cementitious Grout Pad on Concrete Surface 4-48

4-ii Track Structure Design

4.5.3.1.2 Cementitious Grout Pad in Concrete Recess 4-49 4.5.3 1.3 Cementitious Grout Material 4-49 4 5.3.2 Reinforced Concrete Plinth 4-50 4.5.3.2.1 Concrete Plinth in Tangent Track 4-50 4.5.3.2.2 Concrete Plinth on Curved Track 4-51 4.5.3.2.3 Concrete Plinth in Guarded Track with Restraining Rail or Safety Guard Rail 4-51 4.5.3.2.4 Concrete Plinth Lengths 4-52 4.5.3.2.5 Concrete Plinth Height 4-54 4.5.3.2.6 Direct Fixation Vertical Tolerances 4-54 4.5.3.2.7 Concrete Plinth Reinforcing Bar Design 4-54 4.5 3.3 Direct Fixation Fastener Details at the Rail 4-56 4.5.3.4 Direct Fixation “Ballastless” Concrete Tie Block Track 4-57 4.5.4 Direct Fixation Track Drainage 4-59 4.5.5 Stray Current Protection Requirements 4-60 4 5.6 Direct Fixation Special Trackwork 4-60 4.5.7 Noise and Vibration 4-60 4.5.8 Transit Signal Work 4-61 4 5.9 Traction Power 4-61

4.6 EMBEDDED TRACK DESIGN 4-61 4 6.1 Embedded Track Defined 4-61 4.6.2 Embedded Rail and Flangeway Standards 4-62 4.6.2.1 Embedded Details at the Rail Head 4-62 4.6.2.2 Wheel/Rail Embedment Interference 4-63 4.6.3 Embedded Track Types 4-64 4.6.3.1 Non-Resilient Embedded Track 4-64 4.6.3.2 Resilient Embedded Track 4-65 4.6.3.3 Super Resilient Embedded Track (Floating Slab) 4-66 4.6.3.4 A Special Resilient Rail Installation for Vibration Sensitive Zones 4-67 4.6.4 Embedded Track Structure Types 4-67 4.6.4.1 Concrete Slab Track Structure 4-67 4.6.4.1 .I Rail Installation 4-68 4.6.4.1.2 Stray Current Protection Requirements 4-70 4.6.4.1.3 Rail Embedment Materials 4-72 4.6.4.1.4 Embedded Track Drainage 4-75 4.6.4.2 Ballasted Track Structure With Embedment 4-76 4.6.5 Embedded Special Trackwork 4-78 4.6.6 Noise and Vibration 4-79 4.6 7 Transit Signal Work 4-80 4.6.8 Traction Power 4-80 4.6.9 Typical Embedded Concrete Slab Track Design Guideline 4-80 4.6.10 Turf Track: Another Type of Embedded Track 4-84

4.7 REFERENCES 4-86

4-iii Light Rail Track Design Handbook

List of Figures

Figure 4.2.1 Standard Wheel Gauge-AAR (Railroad) 4-3 Figure 4.2.2 (Recommended) Standard Wheel Gaug-Transit System 4-4 Figure 4.2.3 Gauge Line Locations on 115 RE Rail Head 4-7 Figure 4.2.4 Rail Cant Design and Wheel Contact 4-9 Figure 4.2.5 Nytram Plot-Modified AAR-IB Transit Wheel 4-15 Figure 4.2.6 Nytram P/of-l428 Transit Wheel Gauge, 1828 Ax/e Spacing, 25-Meter Curve 4-16 Figure 4.2.7 Nytram Plot-1428 Transit Wheel Gauge, 2300 Axle Spacing, 25-Meter Curve 4-I 7 Figure 4.2.8 Nytram Plot-1415 AAR Wheel Gauge, 1828 Axle Spacing, 25-Meter Curve 4-I 7 Figure 4.2.9 Nytram Plot-1415 AAR Wheel Gauge, 2300 Axle Spacing, 25-Meter Curve 4-l 9 Figure 4.2.10 Nytram Plot-Rotated Truck Position on Track, Transit Wheel Gauge 4-20 * Figure 4.2.11 Nytram Plots-Rotated Truck Position on Track, AAR Wheel Gauge 4-21 Figure 4.2. I2 Filkins- Wharton Diagram for Determining Flangeway Widths 4-23 Figure 4.2.13 Filkins- Wharton Plot to Establish Flangeways 4-24 Figure 4.3.1 Track Transition Slab 4-32 Figure 4.4.1 Ballasted Single Track, Tangent Track (Timber Crosstie) 4-36 Figure 4.4.2 Ballasted Double Track, Tangent Track (Timber Crosstie) 4-36 Figure 4.4.3 Ballasted Single Track, Curved Track (Timber Crosstie) 438 Figure 4.4.4 Ballasted Double Track, Curved Track (Timber Crosstie) 4-38 Figure 4.5.1 Cementitious Grout Pad Design-Direct Fixation Track 4-48 Figure 4.5.2 Concrete Plinth Design-Tangent Direct Fixation Track 4-50 Figure 4.5.3 Concrete Plinth Design-Curved Superelevated Direct Fixation Track 4-52 Figure 4.5.4 Concrete Plinth Design-Curved Superelevated Guarded Direct Fixation Track with Restraining Rail 4-52 Figure 4.5.5 Concrete Plinth Lengths 4-53 Figure 4.5.6 Concrete Plinth Reinforcing Bar Design 4-55

4-iv Track Structure Design

Figure 4.5.7 Rail Cant and Base of Rail Positioning 4-58

Figure 4.5.8 Encased Concrete Crosstie 4-59

Figure 4.5.9 Standard LVT System 4-59

Figure 4.6.1 Embedded Rail Head Details 4-63

Figure 4.6.2 Special Resilient Rail Installation for Vibration Sensitive Zones 4-67 Figure 4.6.3 Concrete Slab with Two Individual Rail Troughs 4-68

Figure 4.6.4 Two-Pour Concrete Slab with Two Individual Rail Troughs 4-68

Figure 4.6.5 Three-Pour Concrete ‘Bathtub” Installation 4-68

Figure 4.6.6 Initial Rail Installations-Base Material 4-69

Figure 4.6.7 Rail Fastening Installations 4-70

Figure 4.6.8 Insulating Surface Barrier at Trough Edges 4-71

Figure 4.6.9 Extruded Elastomer Trough Components 4-72

Figure 4.6.10 Polyurethane Trough Filler with Web Blocks 4-73 Figure 4.6.11 Direct Fixation Fastener with Internal Drain System 4-74

Figure 4.6.12 Cut Away Section Embedded Track Drainage Chase 4-77 Figure 4.6.13 Ballasted Track Structure with Embedment 4-77

Figure 4.6.14 Special Trackwork-Embedded “Bathtub” Design 4-79 Figure 4.6.15 Typical Embedded Track Design 4-81

Figure 4.6.16 Turf Track-Another Type of Embedded Track 4-85

List of Tables

Table 4.2.1 Track Construction Tolerances 4-25

Table 4.4.1 Ballasted Track Design Parameters 4-41

4-v CHAPTER ATRACK STRUCTURE DESIGN

4.1 INTRODUCTION diameter wheels, short stub single wheel axles, and a wide variety of truck axle The design standards for contemporary light spacings and truck centers-all of which rail transit (LRT) track structures, whether in affect the vehicle’s interface with the track an aerial, at-grade, or tunnel environment, structure. In some cases, multiple variations differ considerably from the principles for of these factors can occur on a single car. A either “heavy” rail transit or railroad service. common situation involves smaller diameter The varied guideway environments in which wheels and a shorter truck wheelbase on the an LRT system can be constructed result in center truck of a partial low-floor light rail horizontal and vertical track geometry that vehicle. If these parameters are not carefully often affects light rail vehicle (LRV) design considered in track design, the vehicle’s and performance. Consequently, the light rail tracking pattern can be susceptible to hunting, track designer must consider not only the truck skewing in curves, and unpredictability track geometry, but also the characteristics of at special trackwork. The track gauge-to- the LRV and how it responds to the guideway wheel gauge relationship is especially geometry This is particularly true in important in controlling these operational embedded track located in streets. Embedded performance features. track construction constitutes the greatest challenge to the light rail track designer. In general, reducing the lateral clearance between the wheel flange and rail head, either through increasing the wheel gauge or 4.2 TRACK AND WHEEL GAUGES AND decreasing the track gauge, improves wheel FLANGEWAYS tracking of the rail by keeping the truck square to the rails. This reduces hunting, skewing, The determination of the correct dimensions and flange attack and results in improved to be used for track and wheel gauges and for performance through curved track and special the widths of the flangeways through special trackwork. Vehicle wheel gauge will generally trackwork and other guarded portions of the not vary within a given LRV fleet although track structure is the most critical activity to be cases have occurred where the wheel gauge undertaken during track design. If these and wheel contour of a new vehicle dimensions are not carefully selected to be procurement have not matched that of the compatible with the rail vehicle(s) that will transit agency’s existing fleet. The track unsatisfactory operate over the track, designer should take steps to ensure that the performance and excessive wear of both the vehicle designer does not select wheel track structure and the vehicle wheels will parameters independent of track design. occur. If, as is common, there are several series of vehicles in use on a rail transit line, each with 4.2.1 Vehicle Truck Factors a different combination of truck New, state-of-the-art LRV designs, particularly characteristics, the track designers must “low-floor” LRVs, incorporate many features consider the worst-case requirements of each radically different from heavy rail metros and car series and optimize the track gauge railroads. These may include smaller parameters accordingly.

4-l Light Rail Track Design Handbook

4.2.2 Standard Track and Wheel Gauges 4.2.2.1 Railroad Gauge Practice North American railroads set track and wheel The majority of contemporary rail transit mounting gauges in accordance with criteria systems nominally utilize “standard” track established by the Mechanical Division of the gauge of 1435 mm (56-l/2 inches). This track Association of American Railroads (AAR) and gauge stems from 18th century horse drawn the American Railway Engineering and railways used by English collieries, where Maintenance-of-Way Association (AREMA). track gauge was dictated by the common AAR standard wheel gauge is defined as 55 wheel-to-wheel “gauge” of the wagons used to 1 l/16 inches (equivalent to 1,414 millimeters) haul the coal. This wagon gauge can be and is measured 518 of an inch (15.9 traced back to ancient times, where it was millimeters) below the wheel tread surface. used on Roman chariots because it The AREMA definition of track gauge is approximately matched the center-to-center measured at the same distance below the top distance of a pair of war horses. This made it of rail. These gauge standards have been easier for the horses to follow the wagon ruts incorporated in many contemporary LRT track in the roads. While many different track designs to accommodate possible joint gauges were adopted over the years, none railroad and LRT operations. have proven to be either as popular or practical as standard gauge. If wheels using the current AAR-IB wheel profile are mounted at standard AAR wheel Track that is nominally constructed to gauge, and the wheel and axle assembly is standard gauge can actually be tighter or centered between the rails at standard track wider than 1435 mm depending on a variety of gauge, the horizontal clearance between the circumstances. The track gauge can be wheel and the rail at the gauge line elevation adjusted along the route so as to optimize is 13/32 inch or 10.3 millimeters as shown in vehicle-to-track interaction. Conditions that Figure 4.2.1. This results in total freeplay can require gauge adjustments include track between correctly mounted and unworn curvature, the presence or lack of curve guard wheelsets and exactly gauged rails of 13116 rails, rail cant, and several vehicle design inch or almost 21 millimeters. factors. Vehicle factors include wheel diameter; wheel tread taper and width; wheel It is important to recognize that railroad gauge flange shape including both height and practices generally evolved in a different thickness; the distance between axles; and environment than transit operations. the wheel gauge or distance between wheels Particularly in curved tracks, railroad criteria is mounted on a common axle. predicated on the use of equipment that generally has much larger diameter wheels While nominal standard gauge is nearly than those used on transit vehicles. In universal for both electric rail transit and addition, both the maximum wheelbase and “steam” railroads, different requirements of the number of axles that might be mounted on these modes resulted in appreciably different a rigid truck frame are usually much greater. details, such as where the track gauge is Steam locomotives in particular could have measured, under what conditions it is varied, wheels over 1800 millimeters (6 feet) in and the amount of freeplay that is required diameter, with up to five such sets of wheels between the wheel flanges and the sides of on a rigid frame. Even contemporary diesel the rails

4-2 Track Structure Design

The metric equivalents of the ATEA standard track and wheel gauges were 1,435 and 1,428 millimeters (56-l/2 inches and 56-114 inches), respectively, and were measured 6 millimeters (l/4 inch) below tread height. In addition, some transit systems tightened the track gauge in tangent track, taking advantage of a compound curve gauge corner radius that was rolled into the head of some ATEA girder rails ATEA standards are generally followed by those North American light rail systems that predate the renaissance of light rail transit Figure 4.2, f Standard Wheel Gaug-AAR that began in the late 1970s. European (Railroad) tramways developed similar standards although it is important to note that, in general, locomotives can have wheels that are over 1 European street railways use wheel flanges meter (3.2 feet) in diameter, with three wheel that are even smaller than those promulgated and axle sets on trucks that can have an by ATEA. overall wheelbase of nearly 4 meters (13 feet). By contrast, contemporary rail transit vehicles The transit type standards for wheel gauge rarely have wheels over 711 mm (28 inches) have several advantages: in diameter, never have more than two axles With a tighter gauge relationship, truck per truck, and generally have maximum “hunting”-the lateral oscillation of a truck wheelbase distances no longer than about from one rail to the other as it seeks a 2200 millimeters (7 feet). (Refer to Table 2.1.) consistent rolling radius on all wheels-is The much larger truck features associated more easily controlled. Hunting typically with railroad equipment dictate wheel gauge- is a tangent track phenomenon and is to-track gauge relationships that are far less more prevalent at higher vehicle speeds. stringent than those required for transit The threshold for vehicle hunting is equipment. Hence, railroad gauge and controlled by the stiffness of the primary flangeway criteria should not be adopted suspension. unless both transit and freight railroad Trucks cannot become as greatly skewed equipment will operate jointly on a common to the track, thereby reducing flange bite track. in curving.

4.2.2.2 Transit Gauge Practice Flangeways can be appreciably narrower; Traditional street railway/tramway systems a significant consideration for embedded developed guidelines for wheel gauge that tracks areas with significant pedestrian differ considerably from those used by activity. railroads. In the United States, the most common standards for track and wheel Generally tight wheel gauge-to-track gauge mounting gauges were those promulgated by relationships can only be employed when the the American Electric Railway Engineering transit operator does not have to share its Association (later renamed the American tracks with a railroad Many contemporary Transit Engineering Association or ATEA) LRT systems fall into that category and, as a result, feature a wide variety of vehicle wheel

4-3 Light Rail Track Design Handbook gauges while all generally employing standard shares any portion of its route with a freight track gauge of 1,435 millimeters (56-l/2 railroad, or if future extensions either will or inches). Table 2.1 in this handbook provides might share freight railroad tracks, then selected track and wheel gauge standards of conformance with freight railroad gauge and 17 light rail transit systems currently operating other freight geometry constraints will control in North America. the track design.

As a guideline, Figure 4.2.2 illustrates a When a new light rail system shares track with recommended wheel gauge of 1421 a freight railroad, freight operations normally millimeters (56 inches) for transit use with occur only along ballasted track segments. It standard track gauge. The free play between is unusual for freight trains to share aerial one wheel and rail is 7 millimeters (0.3 inch). structure or embedded track segments of a system. Nevertheless, the mixing of rail freight and LRT operations on any portion of a system will govern track and wheel gauge design decisions for the entire system. Even if the system’s “starter line” does not include joint operation areas, consideration should be given to whether future extensions of the system might share tracks with a freight railroad.

The key issues to consider in accommodating mixed operations are the setting of the back- to-back wheel dimension, guard check gauge, Figure 4.2.2 (Recommended) Standard and guard face gauge criteria that result from Wheel Gauge-Transit System a particular wheel setting. Track design parameters that will be most affected by these decisions include: 4.2.2.3 Gauge Issues for Joint LRT and l The practicality of using available girder Railroad and Mixed Fleet groove and guard rails that are rolled with Operations a specific flangeway width. For a system with a mixed fleet, compromises may be required to accommodate a variety of l The flangeway width and track gauge truck and wheel parameters. This problem is required for effective restraining rail or not new-early 20th century electric street guard rail applications. railway track designers frequently had to l Details for guarding of frog points in adapt their systems to handle not only city special trackwork locations. streetcars with short wheel base trucks and relatively small diameter wheels, but also Transit systems that do not share tracks with “interurban” trolleys that typically had longer a freight railroad may still have a track wheel base trucks and larger diameter connection at the maintenance facility yard for wheels. Some trolley companies even offered delivery of freight cars loaded with track freight service and routinely handled ‘steam” materials or the system’s new light rail railroad engines and freight cars over portions vehicles. If the system’s maintenance of their lines. Today, if the light rail system program contemplates movement of railroad

4-4 Track Structure Design

roiling stock (such as hopper cars full of maintenance-of-way equipment. It is ballast) over portions of the system, it may be imperative that specific notification be given necessary to compromise the track design to that the transit system’s gauge standards accommodate the railroad equipment. This differ from AAR and AREMA standards so that does not mean wholesale adoption of railroad construction and maintenance equipment do standards. Provided that the guard check not damage the track. gauge at turnout frogs allows sufficient space for AAR back-to-back wheel gauge, freight cars can usually be moved over open track 4.2.2.4 Gauge issues for Embedded Track portions of an LRT system at low speeds. It The appropriate track gauge to use in may be necessary to prohibit any railroad embedded track is highly dependent on the equipment whose wheels are not precisely rail section (either tee rail or girder groove rail) mounted, as AAR has tolerances for wheel and the vehicle wheel gauge. In this regard it settings that are considerably more liberal is very important to note that standard railroad than those applied to rail transit fleets. wheel contours (e.g. AAR-IB) and railroad wheel mounting gauges are not compatible Embedded track areas that utilize narrow with narrow flangeway girder rails presently flangeway girder rails typically cannot available from European mills if the track is accommodate movements of railroad rolling built to 1435millimeter (56-112 inch) gauge. stock through curves with radii less than about The backs of the wheels will bind with the 100 meters, regardless of rail section. Other tram or guarding lip of the girder rail causing restrictions on railroad equipment movements one flange to ride up out of the flangeway. If involve the structural capacity of bridges narrow flangeway girder rails are selected, designed for LRT loads and clearances to such as Ri 59N or Ri 60N, it will be necessary trackside obstructions such as catenary poles to adopt either a wide wheel gauge or an and station platforms. equivalent narrow track gauge.

Another category of joint operations is where it If railroad standard wheel gauge must be is proposed to extend an existing “heavy” rail employed on an LRV because some portion of transit operation using light rail technology. the route shares track with a freight railroad, The existing system will already have track wheel clearance to the embedded girder rail gauge, wheel gauge, and wheel contour track can alternatively be achieved by standards in place that must be considered in reducing the track gauge only in those areas the design of the light rail tracks and vehicles where the girder rail is installed. This will for the new system. If the truck parameters of reduce the wheel-rail clearance at the gauge the existing rolling stock, such as truck line and may result in unsatisfactory wheelbase or wheel diameter, are appreciably interaction with railroad equipment. different from typical LRV designs, Embedded track is typically separated from compromises will be necessary to achieve joint use track. Railroad equipment compatible operations. movements, limited to occasional maintenance work trains at low speed, may be Even if neither railroad rolling stock nor mixed acceptable. transit car fleets are a consideration, the trackwork designer should consider the If routine joint operation with railroad freight ramifications that track and wheel gauge equipment along an embedded track area is variations might have for on-track expected, use of narrow flangeway girder rails

4-5 Light Rail Track Design Handbook will not be possible. Wide flangeway girder Toronto to 1,581 millimeters (62-l/4 inches) rails for freight railroad use are provided by on the Philadelphia City system to 1,588 some European rolling mills, but presently millimeters (62-l/2 inches) on the Pittsburgh, available designs of this type are so wide that New Orleans, and Philadelphia Suburban the tram does not provide any guarding action systems. Such gauges were typically for curves or special trackwork. Freight dictated by the municipal ordinances that railroad girder rail flangeways are also granted the streetcar companies their generally wider than desirable for pedestrian “franchise” to operate within the city streets. areas. Such was not the case with girder rails In such legislation it was typically specified made in North America until the mid-1980s; that the rails should be laid at a distance apart however they can no longer be obtained A that conformed with local wagon gauge, near match of the head and flangeway thereby providing horse drawn wagons and contours of North American designs can be carriages with a smoother running surface achieved by milling the head of the lOW80 than the primitive pavements of the era. The structural section available from European only new start transit operation in North mills; however this is an expensive solution America to adopt a non-standard gauge in that requires careful investigation and recent years was San Francisco’s BART justification. “heavy” rail system at 1,676 millimeters (66 inches). This gauge was intended to provide More latitude for joint operations in embedded increased vehicle stability against crosswinds track can be achieved using tee rails rather for a proposed bridge crossing. than girder rails; however a separate flangeway must be constructed and Those systems that employ unusual gauges maintained in the pavement surface. Refer to typically rue the fact because it complicates Section 5.2.2.3 of this handbook for additional many facets of track design, construction, and discussion concerning the possible application maintenance. Contracting for services such of tee rails to embedded track. as track surfacing and rail grinding becomes more difficult and expensive since contractors do not have broad gauge equipment and 4.2.2.5 Non-Standard Track Gauges converting and subsequently reverting In addition to standard 1,435millimeter standard gauge equipment for a short-term (56-112 inch) track gauge, several other assignment is time consuming and expensive. gauges have been used on light rail transit Vehicle procurement is also complicated since systems in North America and overseas. off-the-shelf truck designs must be modified Narrow gauge systems, typically 1,000 and potential savings from joint vehicle millimeters (39-l/3 inches), are relatively procurements cannot be realized. Wide common in Europe, particularly in older cities gauges also preclude joint operation of a rail where narrow streets restrict vehicle sizes. transit line on a railroad route since dual There were once many narrow gauge street gauge special trackwork and train control railways in North America; however the only systems necessary to operate it are both known survivors are the Detroit street car and extremely complex and expensive. the San Francisco cable car system. Broad Accordingly, non-standard gauges are not gauge trolley systems were more common recommended for new start projects. Four traditional trolley operations in North Systems that presently have broad gauge America use broad gauges. These range tracks most likely need to perpetuate that from 1,496 millimeters (58-718 inches) in

4-6 Track Structure Design practice for future extensions so as to head is difficult at best and misleading at maintain internal compatibility in both track worst, it is recommended that gauge elevation and rolling stock design. be defined consistent with railroad practice. For a transit system that is being designed in metric dimensions, designation of gauge 4.2.3 Gauge Measurement Location elevation at 15.9 millimeters (0.625 inches) below top of rail is awkward. Track gauge is measured a specific distance below top of rail because of the gauge corner As a guideline for metric transit track design, it radii of the rail and the flange-to-tread fillet is recommended that track gauge be defined radius of the wheel. The location where at 15 millimeters (0.591 inches) below top of gauge is measured frequently differs between rail. Wheel gauge will be measured at a railroad and transit systems. The customary location to suit the height of wheel flange. gauge elevation point on North American railroads is 15.9 millimeters (0.625 inches) below top of rail. Track gauge on traditional 4.2.4 Rail Cant and Wheel Taper- street railways systems was, and in some Implications for Track Gauge instances still is, measured at either 6.4 millimeters (0.25 inches) or 9.5 millimeters Rail cant is a significant factor in wheel-to-rail (0.375 inches) below top of rail. interface. Cant describes the rotation of the rail head toward the track centerline. It is intended to complement conical wheel treads in promoting self-steering of wheelsets through curves. The cant also moves the vertical wheel loading away from the gauge corner of the rail and toward the center of the ball of the rail. Rails are generally installed at I:40 cant in both tangent and curved track. Figure 4.2.3 Gauge Line Locations on 175 Zero cant is usually specified through special RE Rail Head trackwork so as to simplify the design and fabrication of trackwork components. Canted Rail sections with compound gauge corner special trackwork is now often specified for radii, such as 115 RE section (Figure 4.2.3), high-speed operations over 140 krn/hr (90 do not have a nominally vertical tangent mph). section for gauge measurement at the 6.4- (0.25-inch) or 9.5-millimeter (0.375inch) height, hence the designation of a lower 4.2.4.1 Tapered Wheel Tread Rationale elevation. Older rail sections that were Railway wheel treads are typically tapered to prevalent when the ATEA promulgated its be shaped like a truncated cone. A cone that standards, such as ASCE and ARA rails, had is lying on a flat surface will not roll straight gauge corner radii that were smaller and thus forward but one that is supported on a single more conducive to gauge measurement closer edge-such as a rail-can be made to follow to top of rail. Except for the 100 ARA-B a straight path if its axis is held rigidly at right section, such rail is no longer commonly rolled angles (i.e., by an axle) to the direction of in North America. Since measurement of travel. Railway design takes advantage of this gauge within the curved portion of the rail geometric relationship to facilitate self- Light Rail Track Design Handbook steering of railway trucks through gentle standard transit wheel gauge and tapered at curves without requiring interaction between 1:20, theoretically will begin flanging on the side of the rail head and the wheel curves of radii less than 1350 meters (4,429 flanges. feet).

The usual conicity of the wheel tread is a ratio Wheel profiles that have either a cylindrical of 1:20. This results in a wheel that has a tread surface or only a slight taper, such as greater circumference close to the flange than 1:40, do not self-steer through curves; hence it has on the outer edge of the wheel tread. In flanging is the primary steering mechanism. curved track, this differential moderately Conical wheels that are not re-trued regularly compensates for the fact that the outer rail of also lose their steering characteristics a curve is longer than the inner rail over the because the contact patch becomes same central angle. The wheel flange on the excessively wide as a significant portion of the outer wheel of the axle shifts toward the outer wheel tread matches the contour of the rail rail when negotiating a curve and hence rolls head. Hollow worn wheels develop a “false on a greater circumference while the inner flange” on the outer portion of the tread and wheel flange shifts away from that rail and can actually attempt to steer the wrong way as rolls on a smaller circumference. Thus, the the rolling radius on the tip of the false flange outer wheel will travel forward a greater can be equal or greater than on the flange to distance than the wheel on the inner rail even tread fillet. The importance of a regular wheel though they are both rigidly attached to a truing program cannot be overstated and track common axle and hence have the same designers should insist vehicle maintenance angular velocity. As a result, the axle manuals require wheel truing on a frequent assembly steers itself around the curve just as basis. a cone rolls in a circle on a table top. Note that rolling radius differential is Railroad wheelsets, mounted at AAR standard maximized when the wheel and axle set is wheel gauge and tapered at 1:20, theoretically free to shift laterally an appreciable amount. eliminate flanging on curves with radii over An actual cone has a fixed slope ratio; hence 580 meters (1900 feet). Below that radius, it can smoothly follow only one horizontal contact between the wheel flange and the radius. A wheel and axle set with tapered gauge side of the rail provides a portion of the wheels, on the other hand, can assume the steering action. Nevertheless, tapered wheels form of a cone with a variable side slope by still provide a significant degree of truck self- shifting the free play left and right between the steering that reduces flanging on curves with wheel flanges and the rails. Hence larger radii as small as 100 meters (328 feet) For values of track gauge-to-wheel gauge freeplay sharper curves, flanging is the primary can be beneficial in that regard. steering mechanism. Transit wheels self- steer only on relatively large radii curves, due to the fact that the minimal 6 millimeters (0.2 4.2.4.2 Asymmetrical Rail Grinding inches) of freeplay between wheel gauge and Rail grinding to remove surface imperfections track gauge allows only very limited has been performed for decades, but a recent differential rolling radii on a conical wheel trend has been rail grinding designed to alter before the wheel begins flange contact with the location of the rail contact patch. By the rail. A transit wheelset, mounted at grinding an asymmetrical profile on the rail head, and having distinctly different contact

4-8 Track Structure Design patch locations on the high and low rails of a at 1.20 while the high rail remains at 1:40, given curve, the location of the contact patch then the threshold radius for flanging drops to on the tapered wheel tread can be optimized, about 750 meters (29.5 feet). thereby changing the rolling radius. In theory, a special grinding pattern could be created for $ RAIL j E CONTACT PATCH each curve radius, thereby optimizing the I i 11.89 (0.46W) FOR IO‘ RADIUS ability of a truck to steer through that curve. 7 ! 8 38 (03300') FOR 8' RADIUS

424.3 Variation of Rail Cant as a Tool for Enhancing Truck Steering POTENTIALLATERAL Rail cant variation can improve the rolling WHEELSHIFT 4 (01575') radius differential on standard rail head NO CANT profiles in a manner similar to that achieved by asymmetrical rail grinding. Aside from the 1:40 ( RAIL structural implications of loading the rail closer RAiL cANT-+fCONTACT PATOl ! ; 6.32 (0.2490-) FOR IO- RADIUS to or further from its vertical axis, greater or f ! 509 (OjW2") FOR 8' RADIUS lesser amounts of cant can be beneficial by altering the point on the tapered wheel tread that contacts the rail. Rails installed with no cant create a contact zone or wear strip that is POTENTIALLATERAL WHEELSHIFT 4 (01575') close to the gauge corner of the rail. In rails installed with 1:40 or I:20 cant, the contact I / I patch progresses further from the gauge 1:40 CANT corner of the rail. Note that the greater the rail . ^^ 6 RAIL k C CONTACTPATCH cant, the smaller the rolling radius of a tapered wheel, which reduces the self-steering effect.

Figure 4.2.4 illustrates the theoretical contact patch locations measured from the vertical centerline of the rail. The lateral distance POTENTIALLATERAL between the contact patches for 1:40 and 1:20 WHEEL SHIFT 4 (01575') cants is 6.32 millimeters (0.249 inch) for a rail head radius of 245 millimeters (10 inches). 1:20 CANT This results in a decrease in circumference at Figure 4.2.4 Rail Cant Design and Wheel the contact point of 2.0 millimeters (0.8 Contact inches) for a wheel with a 1:20 taper and a nominal diameter of 711 millimeters (28 Cant differential, in effect, mimics inches). While this may appear to be asymmetrical rail profile grinding. However, insignificant, if the steeper cant is applied to the application of I:20 low rail cant in curved the inside rail, it will increase the amount of track can be considered even if asymmetrical curvature the wheelset can negotiate without rail grinding is practiced. flanging by a significant amount. For example, a trolley wheelset will flange at a The drawback of differential cant is that it 1,350-meter (4,429-foot) curve radius if both requires that curved track employ different rails are at 1:40 cant. If the low rail is canted concrete ties than tangent track. Further, the

4-9 Light Rail Track Design Handbook curve ties would have right and left hand 4.2.6.1 Gauge for Tangent Track orientations that would have to be carefully Light rail transit tracks that are constructed monitored during track construction In direct with conventional tee rails can use standard fixation and timber tie ballasted track at least 1,435millimeter (56l/2-inch) track gauge in two types of rail fasteners-l:40 cant and both tangent track and through moderate I:20 cant-would be required. radius curves without regard to whether railroad (I,41 5millimeters or 55.7087 inches) The benefits of differential cant, like those of or transit design standards are used for wheel asymmetric rail grinding, decline as the gauge. As noted in Section 4.2.2, transit wheels and rail wear. As wheel treads wear wheel gauge varies considerably between toward a flat or hollow profile and rails wear to different LRT operations although 1,421 conform with the wheel profile, self-steering millimeters (55.9449 inches) is recommended. capabilities decline. Once the rail has worn, the contact patch must be restored to its as- Operations that use the tighter freeplay designed location by asymmetric rail profile standard generally have fewer problems with grinding, as it is not practical to modify rail truck hunting. This can be achieved either cant after installation. through widening the wheel gauge or narrowing the track gauge. The former approach is generally recommended. Non- 4.2.5 Track Gauge Variation standard track gauge impacts several aspects of trackwork design and maintenance On an ideal light rail system, there would be including concrete crosstie design, as well as no need for any variations of the track gauge, maintenance operations (such as tamping and thereby producing a completely uniform grinding) undertaken by on-track vehicles. environment for the wheel-rail interface. This is seldom practical, particularly on systems that have tight radius curves or employ narrow 4.2.6.2 Gauge for Curved Track flangeway girder rails. When mixed track The threshold radius at which it may be gauges are employed, the designer should appropriate to alter the gauge in curved tracks consider rail grinding operations and the will vary based on a number of factors related adjustment capabilities of state-of-the-art rail to the vehicles that operate over the track. grinding machines as a means of maintaining Track gauge on moderately curved track can a reasonably consistent wheel-rail interface normally be set at the standard 1,435 pattern. millimeters (56-112 inches) to accommodate common wheel gauges. As curves become sharper, more consideration should be given 4.2.6 Considerations for Determination of to ensure that sufftcient freeplay is provided to Appropriate Gauge prevent wheelset binding. Factors involved in this analysis are the radius of curve under Determination of appropriate track gauge is consideration and wheel diameter, shape of the heart of this section. The sections that the wheel flange, wheel gauge, and wheel set follow detail some of the design conditions (axle) spacing on the light rail vehicle truck. that must be accounted for in gauge design. Systems with mixed fleets and a variety of A recommended analytical procedure for this wheel and axle configurations must consider work is defined in Section 4.2 9 herein. the ramifications associated with each and

4-10 Track Structure Design

develop a compromise among the various generally discouraged, sharp curves cannot requirements. always be avoided.

Conventional wisdom suggests that track Even small gauge increases are usually not gauge must be widened in curved track; possible if railroad contour flanges are used in however this axiom is largely based on combination with narrow flangeway girder rails railroad experience with large diameter because the gauge widening exacerbates the wheels and long wheelbases. By contrast, problem of back-to-back wheel binding. transit vehicles with small diameter wheels, short and narrow flanges, and short The appropriate gauge to be used through wheelbase trucks will often require no track curved track must be determined through an gauge widening in moderately to sharply analytical process. One such method is the curved track. Transit equipment may, development of “Filkens-Wharton Diagrams,” therefore, require track gauge widening on a graphical method developed about 100 any severely curved track segments. For years ago by Wm. Wharton, Jr. & Co., Inc. of trucks with wheel diameters less than 711 Philadelphia. Details of this method are millimeters (28 inches) and axle spacings less described in Section 4.2.9. than 1980 millimeters (6.5 feet), gauge increase will rarely exceed 3 to 6 millimeters Reduction rather than widening of track gauge (l/8 to l/4 inches) even if AAR wheel flanges in curved track has been considered on are used. Conversely, large diameter wheels, several systems in Europe and at one agency large flanges, and long wheelbases will in North America as a way to improve vehicle- require gauge widening at appreciably greater tracking performance when passing through curve radii than for smaller trucks which may reduced radius curves. It is thought that this be incompatible with satisfactory operation on could also reduce wheel squeal by limiting extremely sharp radius curves. As an lateral wheel slip, which is believed to be a example, light rail vehicles with axle spacings main source of such noise. This is an of 1828 millimeters (72 inches), wheel interesting concept that requires further diameters around 650 millimeters (25.5 research and development to generate actual inches) and wheel flange heights less than 20 performance values. Designers should refer millimeters (0.8 inches) typically do not to current professional journals and papers for require any gauge widening for curves with information on this topic that may have been radii greater than above 35 meters. They can published subsequent to printing of this also negotiate extremely small radius curves handbook. as low as 11 meters (36 feet). Vehicles with larger trucks are typically limited to curve radii 4.27 Flangeways of at least 25 meters (82 feet} and may require gauge widening on curves with radii less than Once track gauge and wheel gauge have 60 meters (197 feet). been selected, flangeway widths must be designed that permit free passage of the As a guideline, it is recommended that wheel flange at both special trackwork (e g., systems that have numerous sharp curves frog and frog guard rail flangeways) and on select vehicles with smaller trucks. While restraining rails in sharply curved track curves with radii less than 25 meters are not sections that require track guarding. recommended and less than 50 meters are

4-11 Light Rail Track Design Handbook

The following method of checking track gauge restraining rail bears against the back side of with vehicle truck and wheel profile and the inside wheel, guiding it toward the curve’s determining the minimum flangeway widths is center and reducing the lateral contact force derived from a 1909 report by the Committee of the opposite outside wheel’s flange against on Way Matters of the American Electric the high rail of the curve This essentially Railway Engineering Association (AEREA). divides the lateral force between two contact surfaces and greatly reduces the rate of The primary concern was to establish lateral wear on the high rail. It also reduces Rangeway widths to suit the wheel flange on the tendency of the truck to assume the shape various curves due to the extensive use of of a parallelogram, thereby reducing the angle girder rails on the street railways. The method of attack between the wheel flange and the used was a series of wheel-axle-track gauge rail. In all cases, the use of restraining rail in plots. Similar procedures utilizing computer- a curve will reduce the tendency of the leading aided drafting will be used in contemporary outside wheel to climb the high rail, thereby design considering the various tight radius preventing possible derailments. curves and the various wheel gauges and wheel profiles available. The radius threshold for employing guarded track varies between light rail transit agencies. In addition to track gauge, flangeway widths in Some transit agencies guard any track curves guarded curves must be considered. Where with radii less than 365 meters (1,200 feet), adjustable restraining rail is employed, this is while others do not guard track in curves with dealt with fairly easily. However, girder radii larger than 91 meters (300 feet). Other groove or girder guard rails cannot be readily operations relate the need for guard rails to adjusted and will require special vehicle speed and the amount of unbalanced consideration. superelevation, hence considering the lateral portion of the W ratio before deciding that the expense of guarding is warranted. A system 42.8 Guarded Curves and Restraining with short tramway type wheel flanges will Rails have a greater need for guarding than one that uses railroad type wheels, since the It is customary in light rail track design to lateral wheel loading will be distributed over a provide a continuous guard rail or restraining narrower contact band along the side of the rail through sharp radius curves. The rail head thereby increasing contact stresses. restraining rail provides additional steering In theory, a system whose vehicles are action using the flange of the wheel that is equipped with a self-steering radial truck riding on the inside rail of the curve. By doing design will not need guarded track. so, the lateral over vertical (L/V) ratio at the outer wheel can be reduced, which will both Curve guarding does not usually terminate at reduce wheel and rail wear and deter possible the point of tangency of a curve; it extends derailment. some distance into the adjacent tangent track. This distance depends on a number of factors In a typical LRT installation, the restraining rail including the resistance to yaw of the vehicle’s is installed inside the gauge line of the curve’s suspension system. The conservative low rail to provide a uniform flangeway, designer will extend the restraining rail a typically 35 to 50 millimeters (l-3/8 to 2 distance equivalent to one truck center into inches) wide. The working face of the

4-12 Track Structure Design the tangent track, typically about 10 meters and climb the low rail. The outer restraining (33 feet). When the curve is spiraled, the rail reduces this derailment potential. need for guarding typically ends long before the spiral-to-tangent location In such cases, As a guideline, a typical threshold for curve guarding can usually be terminated a consideration of double guarded track is for distance equivalent to one truck center curves with radii of 30 to 38 meters (100 to beyond the point on the spiral where the 125 feet). instantaneous radius matches the curve guarding threshold. 4.2.8.2 Restraining Rail Design The criteria for beginning curve guarding on Curve guarding on traditional street railway the entry end of the curve is typically the same systems was most frequently achieved using as for the exit end, accounting for the a girder guard rail section similar to that possibility of occasional reverse running train illustrated in Figure 52.1 of this Handbook, operation. As a guideline, the minimum particularly for track embedded in pavement. guarding should begin at the tangent-to-spiral For open track design, such as ballasted or location of a spiraled curve so that the vehicle direct fixation track, a separate restraining rail trucks are straight prior to entering the mounted alongside the running rail is guarding threshold spiral curve. commonly used. The restraining rail itself can be a machined section of standard tee rail, For additional information on curve guarding which can be mounted either vertically or and vehicle steering, refer to Section 429.1. horizontally, or a specially rolled steel shape.

For additional information on various types of 4.2.8.1 Curve Double Guarding restraining rail designs, refer to Section 5.3 of Some transit agencies “double guard” this Handbook. extremely sharp curves, placing a guard or restraining rail adjacent to the high rail as well as the low rail. These installations are 4.2.9 Gauge Determination Analysis designed to counter the tendency of the Requisite track gauge and flangeway second axle on a truck to drift toward the dimensions in curved track must be center of the curve, exacerbating the angle of determined analytically for each combination attack of the outside wheel on the leading of vehicle truck factors. To visualize the axle. In a double restraining rail installation, positions that the wheel flanges assume with the restraining rail alongside the inner fail the rail, a simple and effective graphical shifts the leading axle of the truck toward the technique was developed known as the center of the curve. The outer restraining rail Filkins-Wharton diagram. then guides the trailing axle away from center, helping to ensure that the truck is reasonably A modified version of the Filkins-Wharton square to the track, that both axles are in a diagram, referred to herein as the Nytram nearly radial orientation, and that the truck Plot, has been developed for this Handbook frame is rectilinear rather than taking advantage of the power of computer parallelogrammed. In superelevated, sharp aided design and drafting as an analytical tool. radius track curves where the vehicle speed is The Nytram Plot illustrations, beginning with reduced, the vehicle truck may tend to hug Figure 4.2.5, show horizontal sections of a

4-13 Light Rail Track Design Handbook selected wheel profile that have been derived Wheel Profile Modified 133-millimeter at the gauge line elevation, at the top of rail, (5.2-inch) AAR-1 B* width and, where appropriate, at a restraining rail Wheel Diameter 711 millimeters (28 height 19 millimeters (0.75 inches) above the inches) top of rail. Figure 4.25 illustrates the method Wheel Gauge Transit: 1428 millimeters of establishing the Nytram Plot. (56.25 inches) AAR: 1415 millimeters The plot is derived by sectionalizing both the (55.7087 inches) side view of a wheel of specific diameter with Axle Spacings 1828 millimeters (72.00 designated flange height and the wheel profile inches) in the flange area. Projecting points 0 to 9 2300 millimeters (90.55 from both sections as shown, a horizontal inches) section or “footprint” of the wheel can be Curve Radii 25 meters (82.0 feet) developed at various heights above or below 150 meters (492.1 feet) the top of rail elevation. Using these wheel 228 meters (748.0 feet) sections, the actual vehicle truck axle and * The AAR-1 B wheel profile has been used in wheel positions can be superimposed on a the example for convenience. Transit profile section of curved track to simulate the truck in wheels with alternate flanges may be a radial and skewed position to determine the considered. “attack angle” and wheel clearances. Figure 4.2.6 illustrates a vehicle truck with transit wheel gauge, 1828-millimeter (72-inch) 4.2.9.1 Nytram Plot-Truck-Axle-Wheel axle spacing on a 25-meter (82-foot) radius Positioning on Track track curve positioned on the centerline of Filkins-Wharton diagrams produced manually track perpendicular to the radius line. The were forced to graphically shrink track gauge vehicle wheel plots are taken from Figure and wheelbase in order to depict an entire 4.2.5. To establish the gauge lines of the truck assembly on a reasonably sized drafting track a circle is drawn with a 1435 millimeter sheet. CADD provides the track designer with (56.5inch) diameter centered at the midpoint the ability to develop a full-sized picture of the of the axle. The track gauge lines (inside and entire vehicle truck positioned on a curved outside) are drawn tangent to the diameter of track. These can then either be plotted at the circle. The clearance distances from the reduced scale or selected portions of the wheels to the gauge line of the rails have diagram can be printed at full size. been derived using CADD software and represent the closest point of the wheel plot to To illustrate the methods involved, a series of the gauge face of the rail. Note that these figures have been developed that illustrate the clearances differ (are less than) from the fundamentals of adapting track gauge to calculated wheel gauge-to-track gauge and wheel contour and wheel gauge differences of 10 and 3.5 millimeters (0.4 and positioning of a truck on a segment of curved 0.1 inches) for AAR and transit conditions, track. To understand the impacts of tight respectively. curvature, and the ramifications of different wheel gauge standards and axle spacings, the figures include the following parameters:

4-14 Track Structure Design

19 (3/4") ABOVE TOP OF RAIL RESTRAINING RAIL HEIGHT

711 (28 00') WHEEL OIAMETER-

DESIGN NOTES: 1 TRACK AND WHEEL RELATED DIMENSIONS PERTAIN TO RAILWAY WHEEL GAUGE FOR (56.50’) TRANSIT AND RAILWAY JOINT USE TRACK

2 ALTERNATE WHEEL GAUGE FOR RANSIT USE ONLY TRACK REDUCING THE TRACK GAUGE TO WHEEL GAUGE CLEARANCE IS AN ACCEPTABLE ALTERNATIVE.

3 REFER TO TABLE 2.1 FOR OTHER NA TRANSlT SYSTEM STANDARDS

4. ALTERNATE WHEEL PROFILE IMPLEMENTING LlO (0.39373') FLAT WHEEL FLANGE FOR FLANGE BEARING SECTIONA CLEARANCE SPECIAL TRACKWORK IS AN ACCEPTABLE ALTERNATIVE

5. WHEEL PROFILE SHOWN DERIVED FROM AAR DWG AAR-13 NF3.

figure 4.2.5 Nytram Plot--Modified AAR-1B Transit Wheel

4-15 Light Rail Track Design Handbook

hi1Nl~Ut.d CLEARANCE POINT 25m CURVE - 0.51 (00201”) 150m CURVE - 3 56 (0 1402”) 228~1 CURVE - 379 (0.1492”)

WHEEL GAUGE

------.-.-______._.__ __._____-.-.-.---- _._ -.--.-

SEE FIGURE 42.12 FOR FLANGEWAY MINIMUM CLEARANCE POINT DETAILS BY 25m CURVE - 0.19 (0 0075”) FILKINS-WHARTON 150m CURVE - 347 (01366’) 228m CURVE - 3.73 (0 1469’)

Figure 4.2.6 Nytram Plot-1428 Transit Wheel Gauge, 1828 Axle Spacing, 25-Meter Curve

Similar plots were undertaken with the same similar scenario to the above illustration was truck parameters for track curves with 150- undertaken to establish the clearance and 228-meter (492- and 748-foot) radii. The distances for the three specific track curve clearance results have been entered on this radii. figure The intersection angles between the perpendicular truck and the tangent point to Figure 4.2.8 illustrates a vehicle truck with the track arc have been calculated and are AAR wheel gauge, 1828 millimeter (72-inch) shown for the three curve radii for axle spacing on a 25-meter (82-foot) radius comparison. To determine flangeway widths track curve positioned on the centerline of and wheel attack angle, truck skewing must track perpendicular to the radius line. The be considered as described later in this vehicle wheel plots are taken from Figure section. 4.2.5. A similar scenario to that in Figure 4.2.6 was undertaken to establish the Figure 4.2.7 illustrates a vehicle truck with clearance distances at the wheels and the transit wheel gauge, 2300-millimeter (90.55 intersection angle of the truck wheel to the inch) axle spacing on a 2%meter (82-foot) track arc for the three specific track curve radius track curve positioned on the center of radii. track perpendicular to the radius line. A

4-16 Track Structure Design

MINIMUM CLEARANCE POINT 25m CURVE - -0 34 (-O-0134-) WHEEL PLOT 150m CURVE - 3.38 (0 1331”) 228m CURVE r 3 66 (0 1441) FROM FIGURE 4.2 5 , 1 I -7!-! DIAMETER= STANDARD TRACK mi C GAUGE 2i si -1 -1428 (56 22”) WHEEL GAUGE --.______CENTERLINE OF iTRUCK _ ___ _ - c -.-- -.- .-.-._.___._._.__.______._,-.-_-_-._.~.-.-.- * I “2 2" 'X DIRECTION OF -+wiz TRAVEL 20’ 25m CURVE - t

2300 (90.55”) AXLE SPACING SEE FIGURE 4 2 12 FOR FLANGEWAY MiNlMUM CLEARANCE POINT DETAILS BY 25m CURVE - -0 64 (-0 0252”) FILKINS-WHARTON 15th CURVE - 3 29 (0 1295”) DIAGRAM 228m CURVE - 3 61 (0 1421”)

Figure 4.2.7 Nytram Plot-1428 Transit Wheel Gauge, 2300 Axle Spacing, PSMeter Curve

MINIMUM UEARANCE POINT 25m CURVE - 7.02 (0.2764’) 150m CURVE - 10.05 (0.3957”) 228m CURVE - 10.28 (0.4047”)~ 7 HIFFI. --- PIOT_- r FROM FIGURE 4.2.5

BACK TO BACK zi \ u” 90 I \ I OF WHEELS \.: ei

SEE FIGURE 4.2 12 FOR FLANGEWAY DETAILS BY - MINIMUM CLEARANCE POINT 2% CURVE - 6.67 (0 2626”) 150m CURM - 9.98 (0.3929’) 228m CURVE - 10.23 (0.4028’ Figure 4.2.8 Nytram Plot-1415 AAR Wheel Gauge, 1828 Axle Spacing, 25Meter Curve

4-17 Light Rail Track Design Handbook

Figure 4.2.9 illustrates a vehicle truck with wide gauge at 1435 millimeters (56.5 inches) AAR wheel gauge, 2300-millimeter (90.55 and 1438 millimeters (56.625 inches), inch) axle spacing on a 25meter (82-foot) respectively. Track gauge was widened radius track curve positioned on the center of based on potential wheel binding with 2300- track perpendicular to the radius line. A millimeter (90.55-inch) axle spacing. The similar scenario to that in Figure 4.2.6 was drawing indicates: undertaken to establish the clearance l The sequence of maneuvers required to distances at the wheels and the intersection position the traversing truck in the curving angle of the truck wheel to the track arc for the position. three specific track curve radii. l The angle of attack of the lead wheel to the outside running rail. The above illustrations show the relationships between the various wheel gauges, axles l The measured inside flangeway width to centers, curve radii and the standard track allow outside wheels to touch or barely gauge. Had the wheel to rail clearances touch the outside running rail if a indicated binding or potential binding as in restraining rail is considered. Figure 4.2.7, the track gauge would have to l The wheel positions once the truck has be widened. completed the skew and second wheel contact is made. The above illustrations depict a truck superimposed on a track curve perpendicular For comparison, Figure 4.2.11 has been to the radius line. To simulate the steering developed using AAR wheel gauge with 1828- action of the vehicle truck traversing through and 2300-millimeter (72- and 90.55-inch) axle the various track curves, a set of drawings spacings. with the same truck parameters as above has been developed. The drawings do not account for either potential axle swivel that might be permitted The simulation represents the steering action by a flexible primary suspension system at the of the truck wherein the lead outside wheel on journal box or any possible twisting or racking the truck encounters the curved outside rail of the vehicle truck into a parallelogram resulting in steering or deflecting of the lead configuration. These are conditions that may axle and the truck. Once the outside wheel be inherent in each agency’s vehicle. initially contacts the rail, the wheel action causes the lead axle and the truck to rotate This type of interface study should be about the contact point seeking a second undertaken with the joint involvement of the wheel flange to rail contact point if the curve projects vehicle and track designers. The radius is short and/or the primary suspension drawings do not consider restraining rail; of the truck is relatively stiff. Trucks with however, a measured inside rail flangeway moderate self-steering capability may not width has been stated on the drawings as a encounter the second contact point. reference. If restraining rail is required on a system due to restricted sharp radius track Figure 4.2.10 illustrates two vehicle trucks curves, then a similar scenario should be with transit wheel gauge, 1828-millimeter (72- undertaken using the parameters of the inch) and 2300-millimeter (90.55-inch) axle vehicle truck and track system to establish the spacings on a 25-meter (82-foot) radius track curve. The track gauge is both standard and

4-18 Track Structure Design

MINIMUM CLEARANCE POINT 25m CURVE - 584 (02299”) 150m CURVE - 987 (03886”) r 228m CURE

WHEEL GAUGE

-.- - - - -______._I_____.-- -.-.- -

DIRECTION OF

LSEE FIGURE 4212 AXLE SPACING FOR FLANGEWAY DETAILS BY MINIMUM CLEARANCE POINT FILKINS-WHARTON ic 25m CURVE -2300 6 15 (0 2421’) DIAGRAM 15&n CURVE - 9 79 (0 3854”) 228x CURVE - 10.11 (03980’)

Figure 4.2.9 Nytram Plot-1415 AAR Wheel Gauge, 2300 Axle Spacing, 25-Meter Curve flangeway. For extremely sharp radius curves corner of the outside rail. This will divide the requiring double restraining rails, the same lateral steering force between both wheels procedures are required to establish both and rails. In practice, this condition may not flangeway widths. Truck rotation about an be immediately obtained, however, rail wear initial contact of the inside lead axle wheel on at either the outside running rail or inside the restraining rail face is possible if the restraining rail will eventually balance the designer elects to provide clearance at the curving action. outside lead axle wheel. From the illustrations it is apparent that the AAR wheel gauge requires a wider flangeway than the transit 4.2.9.2 Filkins-Wharton Flangeway wheel gauge due to basic clearances between Analysis the wheel and the rail. Under these same Flangeway widths are a primary concern conditions, it may be necessary to increase when girder rail is to be used in the track track gauge so as to provide either wheel system. contact on both the restraining rail and the outside running rail or to provide clearance Victor Angerer, in a paper before the between the outside wheel and its running rail. Keystone Railway Club (1913), said that “...theoretically for track laid to true ga[u]ge As a guideline, it is recommended that the every combinafion of radius of curve and inside restraining rail flangeway width be set wheel base of truck, with a given wheel to provide dual wheel contact so that the f7ange, calls for a specific width of groove to inside back face of wheel makes contact with make fhe inside of the flange of fhe inside the restraining rail face while the outside wheel bear against the guard and keep fhe wheel is simultaneously contacting the gauge flange of the outside wheel from grinding

4-l 9 Light Rail Track Design Handbook

RESTRAINING FACE 25m CURM - 39.53 (1 5563’) 15Om CURVE - 37.92 (1 4929’) 22&n CURVE - 3778 (1 4874”)

BACK TO BACK

INITIAL POlNi OF CONTACT 1428 TRANSIT WHEEL GAUGE - 1828 AXLE SPACING - 25m CURVE

RESTRAINING FACE 25m CURVE - 43 36 (1 7071:) Dl 15Om CURM - 41.01 (1.6146 ) SECOND POINT 228m CURVE - 40.94 (1 6118’) -r OF CONTACT - 1

BACK TO BACK WHEEL GAUGE -----______.__-.-.- -.-.-.

ATTACK ANGLE DIRECTION OF 25m CURVE - 2.8889’ 150m CURVE - 0 7343’ 228m CURVE - 05852

1428 TRANSIT WHEEL GAUGE - ;N;T~AL POINT 2300 AXLE SPACING - 25m CURM OF CONTACT

TRUCK ROTATION SCENARIO

A LEAD AXLE ROTATED ABOUT CENTER OF TRUCK D CLEARANCES EXISTED BETWEEN ALL OTHER (POINT -A’) TO DETERMINE WHEEL CONTACT WITH WHEELS AND RAIL HEADS RUNNING RAIL (INITIAL CONTACT POINT 61). E USING THIS ROTATED TRUCK POSITION AND 8 HOLDING OUTSIDE VMEEL PowoN (POINT 61) MiEEL NYTRAM PLOT. THE ATTACK ANGLE & ENTIRE TRUCK ROTATED ABOUT LEAD AXLE RESTRAINING RAIL CLEARANCES AS NOTED OuTSlDE WnEEL UNTIL CONTACT WAS MADE WERE DETERMINED AT A SECOND MiEEL LOCATION F. OTHER WHEEL CLEARANCES MAY BE DETERMINED c SECOND CONTACT POiNT WAS ESTABLISHED ON BY A SIMILAR METHOD INSIDE REAR AXLE ~-IEEL (POINT DI AGAINST INSIDE RUNNING RAIL) G TOLERANCES HAVE NOT BEEN INCORPORATED

Figure 4.2.10 Nytram Plot-Rotated Truck Position on Track, Transit Wheel Gauge

4-20 Track Structure Design

SECOND POINT RESTRAINING FACE OF CONTACT FOR 150m CURVi 2% CUR’.‘? - 53 10 (2 0906”) FOR 228m CURVE 15Om CURVE - 51 09 (20114”) 228m CURVE - 50 69 (1 9957”)

WHEEL GAUGE ______-.-- - -.- _.______.-.- - -.-

DIRECTION OF TRAVEL 228m CURVE - 08680

1415 AAR WHEEL GAUGE - OF CONTACT 1828 AXLE SPACING - 25m CURVE

OF CONTACT FOR 150m CURVE RESTRAINING FACE FOR 228m CURVE 2% CURVE - 53.74 (2 1156”) 150m CURVE - 51 15 (20138-) 228m CURVE - 51 07 (2 0106-)

WHEEL GAUGE - -.- - ___ .- i- -.- - ______.-.-----

ATTACK ANGLE DIRECTION OF 25m CURVE - 31325’ 150m CURM - 09768’ 228m CURVE - 0.8144’

1415 AAR WHEEL GAUGE - INITIAL POINT 2300 AXLE SPACING - 25m CURVE OF CONTACT

TRUCK ROTATION SCENARIO A LEAD AXLE ROTATED ABOUT CENTER 0; TRUCK 0. CLEARANCES EXISTED BETWEEN ALL OTHER (POINT ‘A’) TO DETERMINE WHEEL CONTACT WITH WHEELS AND RAIL HEADS RUNNING RAIL (INITIAL CONTACT POINT 81) E USING THIS ROTATED TRUCK POSITION AND B HOLDING OUTSIDE WHEEL POSlnON (POINT 81) WEEL NYTRAM PLOT, THE ATTACK ANGLE & ENTIRE TRUCK ROTATED ABOUT LEAD AXLE RESTRAINING RAIL CLEARANCES AS NOTED OUTSIDE WHEEL UNTIL CONTACT WAS MADE WRE DETERMINED AT A SECOND WHEEL LOCATION F. OTHER WHEEL CLEARANCES MAY BE DETERMINED C SECOND CONTACT POINT WAS ESTABUSHED ON BY A SIMILAR METHOD INSIDE REAR AXLE &EEL (POINT Dl & D2 AGAINST INSIDE RUNNING RAIL) G. TOLERANCES HAM NOT BEEN INCORPORATED

Figure 4.2.11 Nytram Plots-Rotated Truck Position on Track, AA R Wheel Gauge

4-21 Light Rail Track Design Handbook against the ga[u]ge-line and possibly service. Hence girder rails that were rolled for mounting it. It is manifestly impracticable to streetcar systems had much smaller provide guard rails with such a variety of flangeways than those for steam railroads grooves or to change the grooves of the rolled running on paved track in warehouse and rail. The usual minimum of l-9/16 inch is wide wharf districts. These smaller flangeways are enough to pass the AREA standard t7anges on more conducive in areas with pedestrian a 6-foot wheel base down to about a 45foot traffic although it should be noted that AREMA radius, and the maximum width of l-l l/l6 standards for flangeways through grade inches down to about a 35foot radius. On crossings comply with American with curves of larger radius the excess width Disabilities Act (ADA) requirements. should be compensated for by a corresponding widening of the ga[u]ge. If the The Filkins-Wharton diagram analysis was a groove in the rolled rail is too narrow for given simple and effective technique to establish the conditions, it must be widened by planing on flangeway openings required to suit wheel the head side of the inside rail, to preserve the flange profiles, track curve radii and axle full thickness of the guard, and on the guard spacings. The following describes the Filkins- side of the outside rail to preserve the full Wharton diagram procedures.[‘l head. Unusual wheel bases such as 8 feet or 9 feet may require widening of the gage on Figure 42.12 represents an AAR-IB wheel some curves. This widening of gage is placed on 115 RE rail on a 25meter (82-foot) necessary on/y to bring the guard into play radius curve. In the illustration, the wheel is when the groove is too wide for some one adjacent to the rail gauge line. The combination of wheel and flange. In T-rail wheelbase or distance between axles is 1828 curves the guard is formed of a rolled shaped millimeters (72 inches). In the illustration, A-B guard, or a flat steel bar, bolted to the rail. In is the horizontal cut plane passing through the special work and curves in high T-rail track a AAR-1 B wheel profile (W) resting on the 115 girder guardrail is often used. This is RE rail head (R). desirable, as it gives the solid guard in one C-D-E represents the plan view of the section piece with the running rail. The idea that a produced by plane A-B similar to the Nytram separate guard can be renewed when it is worn out does not work out in practice, as it is plot at top of rail. The line C-D-E is perpendicular to the axle. usually the case that when the guard is worn the running rail is also worn to such an extent The length of rail head with a 25-meter that it will soon have to come out a/so.“[‘l (82-foot) centerline radius adjacent to section This excerpt provides still timely guidance in C-D-E is short enough to be considered a straight line. determining flangeway requirements, particularly for design of restraining rail The line F-G represents a perpendicular line systems and evaluating the possible use of to the radius line and forms an intersecting presently available girder rails. angle of 2.0368” to the wheel axis C-D-E. All The tight wheel-to-track gauge freeplay and four wheels will approximately produce a similar angle for line F-G using the small wheel flange profiles that were common combination of curve radius and wheelbase. on traditional street railways required smaller flangeways than those needed for railroad

4-22 Track Structure Design

radial to the track curve. Projecting the points !! of the wheel in plan along the track arc to line !!ii H-J produces the outline K-L-M. !!ii I,ii ii Outline K-L-M represents the absolute iF I, minimum groove section required to permit iI the vehicle truck AAR-IB wheel profile and ii jj OF INSIDE RAIL stated wheelbase to negotiate through the r stated track curvature. Additional flangeway clearances will be required to allow relatively free movement and to compensate for tolerances in the wheel mountings, wheel profiles and track gauge tolerances, which results in a wider flangeway width. Flangeway depth must consider wheel tread wear and special trackwork design features as flange bearing flangeways.

Figure 4.2.13 illustrates the flangeway requirements using outline K-L-M considering both flangeways using Ri 59N rail and

ii I standard track gauge and AAR wheel gauge. ii t ii I L,k-2.0368°i Comparing these results with the Nytram plots and CADD system, similar flangeway requirements are established. The Nytram plot CADD method appears to be a more comprehensive method of establishing flangeway widths and also provides the angle of attack and potential clearances.

PARAMETERS: The above interface issues are basic in . AAR-1EI MODIFIED NARROW FLANGE WHEEL establishing clearances. Research in wheel l 25 METER TRACK CURVE l 1828 (72") Wi-IEEL BASE rail interface has introduced sophisticated rail l 711 (28") WHEEL DIAMETER . 1415 (557087) WHEEL GAUGE head grinding procedures to improve the tracking patterns of wheels as discussed in Figure 4.2.12 Filkins- Wharton Diagram for Section 5.2 of this Handbook. Determining Flangeway Widths

Geometric construction is applied to project the resulting flange profile on the plane H-J. Plane H-J is perpendicular to the rail head and

4-23 Light Rail Track Design Handbook

PROJECTED WHEEL PROFILE (K-C-M) FROM FIGURE 4210 133 (5 l/4') NOMINAL 43 (1 69") MINIMUM FLANGEWAY WlDTH MODIFIED AAR-18 WHEEL 3 l/8' FLANGEWAY CLEARANCE TO COMPENSATE MODIFIED *'-FOk TRA)CK & MEEL GAUGE TOLERANCES AAR-1E VMEEL L-- / 1435 (56.5') TRACK GAUGE RI-59N

TYPICAL WHEEL RAIL INTERFERENCE I IXING TRANSlT & RAllROAD STANDARDS

Figure 4.2.13 Filkins- Wharton Plot to Establish Flangeways

4.2.10 Gauge Implications of Track employed, then construction tolerances Construction and Maintenance may have to be less restrictive. Tolerances l Maintenance Tolerances: These represent the acceptable limits of wear for The most precisely calculated standards for track systems components. After track gauge and flangeways will be of no components are worn to this level, value if the track is not constructed and performance is considered to be maintained in a manner that ensures that the sufficiently degraded such that wear is design intent is achieved in practice. likely to occur at an accelerated rate. At Obviously, perfectly constructed and that time, maintenance should be maintained tracks are not possible, and the performed to restore the system to a cost of achieving such would probably exceed condition as close as possible to its new, the value of benefits that would ensue. as-constructed state. Accordingly, tolerances must be specified that both protect the design objective as closely as l Safety Tolerances: These represent the possible and are practical and achievable with levels beyond which the system is unsafe the materials and equipment available. for operation at a given speed. The FRA Track Safety Standards are a well-known Tolerances fall into three categories: example. If track systems are permitted l Construction Tolerances: These will be to degrade to an unsafe condition, the strictest. Track construction performance will be unsatisfactory, wear tolerances are most often specified with will be excessive, and the cost of the use of new materials in mind. If used restoration to a satisfactory state will be materials, such as relay grade rail, are high.

4-24 Track Structure Design

The reduced differential distance between tolerance limits is important in both the track gauge and wheel gauge in transit longitudinal track surface (vertical) and systems governs the gauge tolerances for alignment (horizontal) planes. both. The practice is to have a plus tolerance for track gauge and a minus tolerance for Table 4.2.1 lists recommended track wheel gauge. construction tolerances for the three general types of track construction. Track Transit track construction tolerances are more maintenance limits that define allowable wear restrictive than conventional railroad and surface conditions are not included, as standards The tolerances apply to the they should be developed with the needs of a following track standards-track gauge, guard particular transit operating agency in mind. rail gauge, cross level and superelevation, Future updates of this Handbook should vertical track alignment and horizontal track include guidance on the development of alignment. The rate of change within the maintenance tolerances.

Table 4.2.1 Track Construction Tolerances Construction Tolerances Location Tolerances Type of Track and Cross Horizontal Vertical Horizontal Vertical Track Guard Rail Level w Alignment Alignment Alignment Alignment Gaugeo DeviatiorW) DeviatiorWs) Variable(@ Variable@ Ballast (Main +3 +(0.1250") 3 (0.125on) 6" (0 25""') 6'2' (0 25"(2)) 15 (0.3937") 15 (0.3937") Line) -0 -(0.0000")

Direct Fixation +3 (+O 1250") 3 (0.1250") 6"' (0.25"'") 6" (0 25"") 10 (0 3937") 10 (0.3937") -1 (-0.0625")

Embedded +3 (+0.1250") 3 (0.1250") 6s (0.25"") 3""W (0~,250"'3"4') 6 (0.2500") 6 (0.2500") -1 (-0.0625")

Ballast (Yard) +4 (+0.3125") 4 (0 3125") 9 (0 3750") 9 (0.3750") 15 (0.5906") 15 (0.5906") -1 (-0.0625")

NOTES: (1) Deviation is the allowable construction discrepancy between the standard theoretical designed track and the actual constructed track. (2) Deviation (horizontal) in station platform areas shall be: 0 millimeters (inches) toward platform, 3 millimeters (0.125 inches) away from platform. Refer to Figure 2.8.1. (3) Deviation (vertical) in station platform areas shall be: plus 0, minus 6 millimeters (0.2500 inches), or in conformity with latest American with Disabilities Act requirements. Refer to Figure 2.8.1. (4) Deviation at top of rail to adjacent embedment surface shall be plus 6 millimeters (0.2500 inches) minus 0. (5) Rate of change variations in gauge, horizontal alignment, vertical alignment, cross level and track surface shall be limited to 3 millimeters per 5 meters (0.1250 inches per 16 feet) of track. (6) Variable is the allowable construction discrepancy between the overall location of track and the actual final location of the constructed track. (not to be confused with tolerances pertaining to track standards). Tracks adjacent to fixed structures shall resort to deviation limits.

4-25 Light Rail Track Design Handbook

4.3 TRACK SUPPORT MODULUS simply as the amount of deflection in these springs from a given wheel load. The greater Railway track acts as a structural element that the deflection, the lower the modulus. undergoes stress and strain as a vehicle Conversely, a track with little deflection has a passes over the track. The rail, fastener, tie, high modulus, which is generally considered ballast, subballast, and subgrade are each a important for ride quality and good component of the track structure. Each serviceability. Most of the deflection of the undergoes some deflection as the wheel track structure occurs in the ballast and passes. The analysis of how the track subgrade, with only small deflections at the structure reacts to wheel loads has been rail and tie. In order to minimize deflections, studied analytically since Professor Talbot the track designer must focus on a thick and his committee wrote the first definitive section of well-compacted ballast and work on this subject in 1918 for AREMA. This subballast with a sound dry compacted Handbook provides sufficient information to subgrade. This is crucial if total deflections for design track; for additional reference, the ballasted track are to be kept under the 6- designer is advised to study either the Talbot millimeter (0.2-inch) limit suggested by Reports of 1920 or Dr. Hay’s Railroad AREMA. Engineering, which both provide a more detailed explanation. g51 In direct fixation track, the track modulus is much higher because the rail fasteners are Track modulus is an important subject, with made of neoprene and/or rubber which have a complex mathematical calculations, to allow controlled restricted deflection. for track analysis as a structure to determine appropriate rail weights, tie size and spacing, When rails are embedded directly into ballast depth, the need for subballast, and the concrete pavement, the modulus becomes need for special subgrade preparation for very high since there is almost no deflection ballasted track. Similar mathematical by rigid pavements. calculations are undertaken for direct fixation track. The following explanation deals with ballasted track modulus, which can be determined using The track modulus factor value (p) established the following equation?] in this section is a requirement of track design P = -UY (1) and one of the variables used in the calculations for ballasted track structural where: p is the upward pressure per unit design (Section 4.4.3) and direct fixation track on the ballast or sub-ballast structure design (Section 4.5.3). In addition, U is a factor determining the the track modulus is a parameter found in track stiffness or “modulus of many of the calculations used by noise and track” vibration engineers when considering wheel Y is the vertical deflection impacts, contact separation and velocities. measured at the base of rail

4.3.1 Modulus of Elasticity[21 The modulus of track is defined as the vehicle load per unit length of rail required to deflect Ballasted track is often characterized as a the rail one unit. An example follows. beam supported on a continuous series of springs. Track modulus can be defined

4-26 Track Structure Design

Assume a wheel load of 9,090 kilograms 4.3.2 Track Modulus of Various Track (20,000 pounds), converted to an 88,960-N Types force, results in a track vertical deflection of IO millimeters (0.394 inches) The force The stiffness of rail, fastenings and supporting required to deflect the track 25.4 millimeters (1 structure determines the stiffness of track. inch) is: The types of track encountered on an LRT system-ballasted, direct fixation and embedded-have a wide range of stiffness because the components of each track P = 225,960 N LP = 50,761 Ibs. 1 substructure are dramatically different. Ballast provides the most flexible track Expressed (in metric) for a deflection of 1 structure support, while embedded track is millimeter, force per unit deflection is thus: usually the stiffest. P 225,960 Pu c-z = 8,896N/mm 25.4 25.4 4.3.2.1 Ballasted Track Determination of track modulus for ballasted 50,761 P= - = 50,761 lb./in track can be made by strictly following the lin L _I Talbot formula shown in Section 4.3.1

In many cases for ballasted track, the The force required to deflect the track per unit; maximum rail deflection is not known, or the i.e., 1 millimeter (1 inch), with track tie spacing maximum rail deflection is to be estimated at 760 millimeters (30 inches) is: from a given track structure. The latter PU 8,896 or- = 1 I.7 N/mm/mm or N/mm* condition is frequently encountered in Tie Spacing 760 ballasted trackwork design. 50,761 The track modulus can be estimated - 30 = 1,692 Ibs./in./in. or psi 1 considering the crosstie size, structure depth The above calculated force required to deflect of subballast and ballast, type of ballast rock one rail on one tie 1 millimeter with a tie or stone, and the crosstie spacing. As a spacing of 760 millimeters is known as the guideline, track modulus using 115 RE rail modulus of track elasticity. section can be expected to be in the following ranges:

The above analysis assumes that the rail l S-17 N/mm2 (1500 - 2500 psi): 450 deflection is either known, or that maximum millimeters (17.7 inches) depth of sub- rail deflection is the primary criteria for the ballast and limestone ballast, timber ties track design. Developing a high track spaced at 550 millimeters (22 inches) modulus without increasing the weight of rail . 17-24 N/mm2 (2500 - 3500 psi): 550 will dramatically reduce the bending moments millimeters (21.7 inches) depth of well- in the rail. compacted subballast and heavy stone ballast, timber ties spaced at 550 millimeters (22 inches)

l 24-34 N/mm* (3500 - 5000 psi): 600 millimeters (23.6 inches) depth of well-

4-27 Light Rail Track Design Handbook

compacted subballast and heavy granite spring rates vary widely. Two popular spring ballast, timber ties spaced at 520 rate ranges are: millimeters (20.5 inches) 15,780 to 24,540 N/mm (90,000 to 140,000 lb./in) Track modulus has been known to vary and and lose stiffness with a change in applied load; 42,060 to 56,080 N/mm (240,000 to that is, modulus under a 63,500-kilogram (70- 320,000 lb./in) ton) car may have a lesser value when measured under a 90,700-kilogram (loo-ton) Fastener spacing, like the spacing of ties in car: A modulus of 13.8 to 17.3 N/mm* (2000- ballasted track, is a factor in the stiffness of 2500 psi) represents good timber tie ballasted direct fixation track; a common spacing for track. The value can, and most likely will, rise fasteners is 760 millimeters (30 inches). The to 34.6 to 55.3 N/mm* (5000-8000 psi) for spring rate in direct fixation fasteners is often track with concrete cross ties spaced at adjusted to mitigate ground borne vibrations. 610 millimeters (24 inches). This adjustment then affects the track modulus. 4.3.2.2 Direct Fixation Track The following is an example on establishing As stated above, the track stiffness or the the modulus of track elasticity for direct amount of vertical deflection of the track fixation track: structure under vehicle load is the basis for P determining the track support modulus. -= P Unlike ballasted track, however, the track S where component deflections and elastic properties of direct fixation track are generally known. In p is the upward pressure per unit length on the fastener direct fixation track, the vertical deflection s is the fastener spacing occurs in the: u is a factor determining the track stiffness also known Bending of the rail as the “modulus of track” Elastomer portion of the direct fixation p is a pre- determined value based on the spring rate of fastener the direct fixation fastener elastomer as stated above Intermittent seating of the direct fixation s is a set value based on the desired direct fixation fastener to the concrete or at the layers of fastener spacings - 760 millimeter (30 inch) spacing vertical shims below the fastener P 17,530 Intermittent seating of the rail at the rail -=-= 23,1N/mm/mm seat S 760 100,000 Flexure of the direct fixation slab at the = 3,333 Ibs/in./in. supporting subbase materials for at-grade 30 1 installations. P 52.,580 -=- = 69.2Nlmmlmm S 760 The track modulus of direct fixation track is 300,000 determined by establishing the nominal spring = 10,000 Ibs/in/in rate of the elastomer component of the direct 30 1 fixation fastener. Elastomer vertical static

4-28 Track Structure Desian

The above calculated force required to deflect structural support, or where only elastomeric one rail on one fastener 1 millimeter with a side pieces are used, the track modulus is fastener spacing of 760 millimeters is known identical to the direct fixation track analysis as the modulus of track elasticity. indicated in Section 4.3.2.2.

The track moduli calculated above are It is more difficult to determine the track somewhat understated. The dynamic spring modulus for most embedded trackwork rate of most elastomeric direct fixation rail designs for the following reasons: fasteners are 10 to 50% higher than the static l The rail is continuously supported. The spring rate. Dynamic spring rate can be most Talbot premise of beam supports on an easily visualized by considering that the elastic foundation does not apply elastomer has not fully recovered, or is in l Rail deflections can be extremely small. various stages of resonance, when the next wheel load is applied. l The spring rate for the rail support material is not known or easily The net effect of the dynamic spring rate is to determined. increase the effective spring rate and thus the track modulus. Most direct fixation rail Track modulus values have very little meaning fasteners show an increase of 30% in spring for designs where the rail is completely rate during dynamic qualification testing. The encased in concrete. Rail deflections, if any, static track moduli calculated above should be are in the range of 0.025 millimeters (0.001 multiplied by 1.30, unless rail fastener test inches). The corresponding track modulus is results indicate that another value is more extremely large, and may even be dependent appropriate. on the deflection of the underlying track slab. The slab deflection is also a minor value.

4.3.2.3 Embedded Track An embedded track design with limited The track modulus for embedded track is very resiliency, such as the rail trough liner design dependent upon the design of the rail support used in Baltimore and Seattle, is known from and underlying base slab. field measurements. In Baltimore, the embedded rail trough features a 2.3-millimeter For embedded ballasted tie track with (90-mil) thick polyethylene lining at its pavement overlay, the track modulus is in the perimeter for stray current mitigation and range of ballasted track, 10.4 to 31.1 N/mm2 limited resiliency. Track measurements taken (1,500 to 4,500 psi). See Section 4.3.2 1 for under a 53.375-N (12,000-pound) wheel load ballasted track modulus values. If the indicated that the rail deflected from 0.050 to pavement extends down into the ties, and 0.25 millimeters (0.002 in to 0.010 inches). especially if the pavement is constructed This corresponds to an average force per unit underneath the ties, the track structure deflection of approximately 356,000 N/mm behaves more like a slab. Ballasted track (2,000,OOO lb./in). As the force per unit equations are not valid for the latter case. deflection and track modulus are identical for continuously supported track, the track Some recent embedded track designs are modulus is thus seen to be 356,000 N/mm2 essentially direct fixation trackwork installed in (2,000,OOO psi). Similar track moduli would be troughs formed in an underlying concrete slab. expected from a fully encased high grade Where the infill material provides little or no polyurethane fill.

4-29 Light Rail Track Design Handbook

A more complex evaluation would be needed where the transit vehicles operate at speeds for a design that uses rigid fastener plate greater than typical yard operation, the supports. For concrete infill, the track ballasted track will invariably settle and the modulus would be extremely large. For an stiffer track will incur structural damage. The elastomeric or asphalt infill, the track modulus passengers will experience an abrupt would be calculated from the rail deflection transition in the form of vertical acceleration, between rigid supports using conventional similar to hitting a bump in the road with a car. structural continuous beam formulas. Track modulus can vary dramatically among Finally, a rail boot or similar continuous various track types. Well-maintained elastomeric pad under the rail may be ballasted track, where timber or concrete incorporated in the embedded trackwork crossties are supported by a stipulated depth design. of ballast and sub-ballast, can have a track modulus as low as 17.2 N/mm* (2,500 psi) or Representative track moduli may be estimated as high as 48.3 N/mm* (7,000 psi). Concrete from values for data from one manufacturer crosstie and timber crosstie track with elastic It uses a 50 Durometer elastomer with an 8- rail fastenings tend toward the higher end of millimeter (0.3-inch) thickness at the rail base. the scale. Embedded or direct fixation track, The elastomer is ridged for additional where a concrete base slab supports the rail, resiliency. The track modulus from this typically have a higher modulus value and design is approximately 1037 N/mm2 (150,000 greater stability as do non-ballasted “open” psi). An additional elastomer layer is optional deck bridge structures where the rail is with this design, increasing pad thickness to supported on rigid structural abutments and 19 millimeters (0.75 inches). The track spans. modulus is decreased to 207 N/mm* (30,000 psi).L31 Note that the track modulus change is Locations where the track modulus changes not a linear function of elastomer thickness in abruptly are prone to vertical alignment this case, but varies in accordance with problems, particularly when the predominant elastomer pad shape. traffic moves from the stiffer to the more flexible track. A typical example is the Where the assumption of a linear elastomeric interface between an open deck bridge and pad deflection is reasonable, a rough estimate adjoining ballasted track. Railroads have long of track modulus can be obtained by using a been aware of track alignment problems in rail deflection of 15% of the elastomer pad these areas and have attempted to thickness.r41 compensate by installing transition or approach ties similar to those shown on AREMA Plan No. 913-52. Various 4.3.3 Transition Zone Modulus arrangements of long-tie installations are used on different railroads, sometimes with an 4.3.3.1 interface Between Track Types incremental decrease in the crosstie spacing. The interface points between embedded and The objective of these designs is to gradually ballasted track segments and between direct stiffen the ballasted track structure over an fixation and ballasted track are typically extended distance, thereby reducing the locations of sudden changes in track modulus. abrupt change in track stiffness at the bridge If special design consideration is not given to abutment. Transition tie arrangements have such areas, particularly in line segments

4-30 Track Structure Design also been placed at the ends of concrete tie wheel load leaving the stiffer track section. installations where the track modulus The rail shows a downward deflection differential between the concrete and timber approximately 1 meter (3 feet) from the crossties often results in additional surface transition point or end of direct fixation or maintenance requirements. Similar conditions embedded concrete slab, with a resulting repeatedly occur on transit track installations upward force approximately 1 meter (3 feet) between ballasted track and both embedded into the direct fixation or embedded track and direct fixation track. Special transition portion. The rail sine wave disturbs the track design must be considered to maintain ballasted track and attacks the direct fixation an acceptable ride quality at these locations or embedment track installations, leading to without incurring excessive maintenance deterioration of components and track costs. conditions.

4.3.3.2 Transition Zone Design Details 4.3.3.3.1 Transition from Direct Fixation In North America, the current standard to Track to Ballasted Track compensate for the track modulus differential The ballasted track side of the transition zone, is to use a reinforced concrete transition slab even with a transition slab, cannot (also called an approach slab) to support the consistently produce a uniformly varying track ballasted track. These transition slabs modulus due to the tendency of ballast to (Figure 4.3.1) extend from the end of the compact, pulverize, and become fouled. Such abutment or the embedded track slab, a deterioration leads to settlement voids, hard minimum of approximately 6 meters (20 feet) spots, and pumping track. Regular into the ballasted section. The top of the slab maintenance of the ballast is needed to typically is located 300 millimeters (12 inches) protect the rails and maintain ride quality. below the bottom of the ties immediately adjacent to the stiffer track, gradually Fortunately, direct fixation fastener design increasing to 350 millimeters (14 inches) at continues to evolve and a greater range of the far end of the slab. This design replaces fastener spring rates is now available. A direct compressible subballast materials with a fixation track modulus of 23.1 MPa (3,333 lb/in stiffer base, while also gradually decreasing per inch of rail), which compares favorably the thickness and compressibility of the with standard concrete crosstie installation, is ballast layer. Center-to-center distances now possible. Softer direct fixation fasteners between track crossties are generally reduced in the zone immediately adjacent to the in the transition slab section to provide ballasted track transition zone can alleviate additional stability and increase the track some of the transition problems that are not modulus. However, even a well-designed addressed by conventional transition slabs. transition zone will experience some track surface degradation during operation, 4.3.3.3.2 Transition from Embedded Track requiring periodic inspection and resurfacing to Ballasted Track to avoid pumping track conditions. Embedded track design continues to evolve and improve; however, the rail deflections that would be required to match typical ballasted 4.3.3.3 Transition Zone improvements track modulus values are difficult to achieve in The action of the rail at a transition zone embedded track. The track sine wave represents a sine curve produced by the

4-31 Light Rail Track Design Handbook

PROYlDE CLEATS OR GAUGE LINE OF RAIL COURSE SURFACE -65 (2 l/2") FLARE TO LOCK IN BALLAST-, 45 (I 314-j FLANGEWAY 50 (2' MIN.) WHEEL I If CLEARANCE DE:PRESSiON 1 / / rTD? OF EMBEDDED IN CONCRETE II I I SECTION

1 BALLAST 115 RE RAIL Top OF BALLAST EMN WITH BOTTOM OF EMBEDDED TROUGH

DETAIL OF BALLASTED SECTION SUPERIMPOSED TYPICAL TRACK & SLAB INSTALLATION ON END SECTION OF EMBEDDED TRACK 115 RE RAIL FLANGEWAY FLARE

OUTLINE OF TRANSInDN

BALLASTED / EMBEDDED TRACK PLAN \nEW

BALLASTED TRACK INSTALLATION ., EYBEDDED TRACK INSTALLATION FIRST POUR CONCRETE e OF flRST TIE-+ 1 TIE SPACING PER_,. 10 CONCRETE TIES SPACED AT 610 (24') CENTERS I I --- I__..

406- -305 TOP OF SUBGRAD+ (16-l' (12’) SUBBALLAST BASE PAD TRANSITION SLAB il 6100 (20'-0') m L

==-@ TRANSITION BEMEN BALLASTED TRACK AND EMBEDDED TRACK INSTALLATIONS

Figure 4.3.1 Track Transition Slab

4-32 Track Structure Design phenomenon in the rail places extremely high section of the transition rail could also be bending forces in the contained rail within the continuously varied to provide a stiffness embedded track immediately adjacent to the gradient suitable for the purpose. The ballasted-to-embedded track transition point. transition rail of sufficient length (IO The differential in track modulus between meters (32 feet)) would straddle the embedded and ballasted track may be too interface point. large to overcome by introducing a flexible rail support in the area adjacent to the interface. Whatever design is developed, it should be compatible with conventional concrete or timber crosstie fastenings, direct fixation 4.3.3.3.3 Design Recommendation fasteners, and installation within the selected The track designer must eliminate the embedded track design. pronounced sine curve action in the rail at the transition zone. Eliminating or reducing the sine curve is more achievable in direct fixation 4.4 BALLASTED TRACK track than in embedded track using conventional track components. The following Ballasted track is the most prevalent track recommendation applies to both types of track type used in light rail transit. While ballasted transition interfaces. track for light rail transit resembles conventional railroad track in appearance, its The sine curve may be reduced to a functional design may have to contend with issues such level by stiffening the rail in the vertical axis. as electrical isolation and acoustic A stiffer rail will act as a beam to bridge the attenuation. In addition, it may be required to crucial transition point. The beam or stiffer rail accommodate continuous welded rail on an section should project a minimum of 5 meters alignment that includes curves far sharper and (16.4 feet) in each direction from the transition grades far steeper than would ever be interface point. Rail stiffening can be achieved encountered on a freight railroad or even a by several means; the following are suggested “heavy rail” transit route. procedures: l Attachment of a standard joint bar section Proper design of the roadbed and ballast to the rail with standard track bolts, spring elements of the track structure is a key issue. washers and heavy duty nuts. The It is essential in providing an adequate standard joint bar section would straddle foundation for the track so as to minimize the interface point. future maintenance requirements. Roadbed and ballast sections should be designed to l The use of an inherently stiffer rail section minimize the overall right-of-way width, while across the interface. If the standard providing a uniform, well-drained foundation running rail section is 115 RE, the use of for the track structure. thick-web 115 TW, could provide the required bridging effect. A special transition rail section could also be 4.4.1 Ballasted Track Defined machined from the European heavy blank rail section 180/105. The ends of the Ballasted track can be described as a track transition rail section could be machined structure consisting of rail, tie plates or to provide a pressure weld connection to fastenings, crossties and the the adjacent running rail. The cross ballastisubballast bed supported on a

4-33 Light Rail Track Design Handbook

prepared subgrade. The subgrade may be a l Track gauge compacted embankment, an excavation or cut l Guarding of curved track and restraining section, or a bridge structure. Ballasted track rail features is generally the standard for light rail transit l Rail fastenings and tie plates routes that are constructed on an exclusive l Type of track tie and corresponding track right-of-way outside of a central business structure to suit operations district.

Ballasted track can be constructed to various 4.4.2.1 Ballasted Track Rail Section and designs, depending on the specific Track Gauge requirements of the transit system. Refer to Section 4.2 and Chapter 5 of this Depending on the portion of the system under Handbook for guidance on determining rail design, a satisfactory ballasted track design section, track gauge, and flangeway could be anything from timber crossties with requirements. conventional tie plates, cut spikes, and rail anchors, to concrete crossties with elastic rail 4.4.2.2 Ballasted Track with Restraining fastenings that incorporate insulating Rail components. While the loadings typically are Refer to Section 4.2.8 herein for determining limited to those of the light rail vehicles only, requirements, locations and limits for guarding heavier loading standards may be required. track with restraining rail. Specific details for Ballasted track may need to accommodate various types of restraining rail designs are freight railroad loadings where the track is to included in Chapter 5. be shared with a commercial railroad. Light rail structural loading is one-quarter to one- third of that imposed on freight railroad tracks. 4.4.2.3 Ballasted Track Fastening Refer to Section 5.4 for requirements Prior to developing a ballasted track design, concerning crosstie rail fastenings. several vehicle/track related issues must be resolved, including: vehicle wheel gauge, wheel profile, and truck design; the track 4.4.3 Ballasted Track Structure Types gauge and rail section; and the ability of the vehicle to negotiate the track in a satisfactory There are generally two standard designs for operational manner. These are addressed in track structures on ballasted track. other chapters of this Handbook. If the track l Timber crosstie track is to be located in an acoustically sensitive l Concrete crosstie track area, the designer should also consider noise and vibration mitigation measures as Ballasted track design can result in a suitable discussed in Section 4.4.10. track structure using either timber or concrete crossties. The differential track support or track modulus dictates the quality of the track, 4.4.2 Ballasted Track Criteria the ride and future maintenance requirements. Concrete crosstie ballasted track provides a To develop ballasted track design, the more reliable track gauge system and tighter following track components and standards gauge construction tolerances. This results in must be specified: a smoother ride with less differential track l Rail section settlement.

4-34 Track Structure Design

Chapter 2 documents the types and crosstie/concrete crosstie) and corresponding magnitudes of loads transferred from the track structure resiliency or track support vehicle wheel to the rail. The rail must stiffness. support the vehicle and the resulting loads by absorbing some of the impact and shock and Rail supported on timber crossties and a transferring some forces back into the vehicle moderate ballast/subballast section, results in via the wheels. The initial impact absorber on a track modulus range of 14 to 17 N/mm* the vehicle is the elastomer in the resilient (2,000 to 2,500 lb /inch per inch of rail). wheels (if used) followed by the primary suspension springs and then the secondary Resilient rail base pads are placed on suspension system. The initial impact concrete crossties, both to protect the absorber on the track is the rail, specifically concrete tie seat and to impede the impact the rail head, followed by the fastening or and vibration associated with wheel passage supporting system at the rail base and then from migrating from the rail to the crosstie. the remaining track structure. A resilient rail They are a determining parameter of track seat pad is used to absorb some of the force modulus. A reduced pad height (6 millimeters on concrete crossties On timber crossties or 0.2 inches) and a very stiff elastomer or the resiliency in the wood itself acts as the polyethylene pad produce a stiff track support absorber. All components absorb and resulting in an increased rail support modulus. distribute a portion of the load. Rail supported on concrete crossties and an Many transit systems have used both timber ample ballasffsubballast section results in a and concrete crossties. In some instances, track modulus range of 31 to 45 N/mm* (4,500 the main line track on new installations was to 6,500 lb/inch per inch of rail). constructed using concrete crossties with standard rail insulation. Regardless of the 4.4.3.2 Timber Crosstie Ballasted Track type of main line crossties, yard maintenance On many light rail transit systems constructed facility tracks are generally built with timber in the early 198Os, timber crossties were crossties either with or without insulated considered to provide sufficient electrical fasteners. The track structure’s design isolation. Some projects, including those that (degree of resiliency) dictates the amount of reconstructed existing trolley systems, did not load distributed to the rail and track structure take extraordinary measures to insulate the . and the magnitude of force returned to the track because other measures were either wheels and vehicle. taken or in-place to control traction power stray current. Contemporary designs typically 4.4.3.1 Ballasted Track Resilience incorporate insulation systems within the Ballasted track design allows partially crosstie rail fastening to control stray currents controlled rail deflection in both the vertical close to their source. Typically, non-insulated and horizontal directions. This phenomenon rail fastenings are employed only in yard of rail action contributes to successful track tracks, where the yard has its own traction operation by distributing the load to the power substation and stray currents are surrounding track components and structure. unlikely to leave the site. Non-insulated, ballasted track may also be used in rights-of- Specific track design decisions must be made way where there are no parallel utilities. regarding the type of track structure (timber

4-35 Light Rail Track Design Handbook

Timber crosstie ballasted track consists of the 4.4.3.2.1 Timber Crosstie Fastening rail placed on a tie plate or rail fastening Conventional tie plates, cut spikes and rail system positioned on the crosstie which is anchors were sufficient to establish a supported by a ballast and subballast ballasted track installation using timber trackbed as shown in Figures 4.4.1 and 4.4.2 crossties for railroad and earlier contemporary for single- and double-track, respectively. transit track. However, current track design generally includes protection of the negative return rail from stray electrical currents.

SUBJECT TO SlTE SPECIFICS AND REOUIREMENTS FOR CATENARY POLES (REFER TO CHAPTER 3)

N BASE OF RAJL AND

L SUBBALLAST LBALLAST DEPTH SUBBALLAST DEPTH SUEGRADE

Figure 4.4.1 Ballasted Single Track, Tangent Track (Timber Crosstie)

2500 (98") NOM. SUBdCT TO SITE SPECIFICS AND REOUIREMENTS FOR CATENARY POLES BETWEEN TRACKS (REFERTO CHAPTER3)

RAIL AND FASTENIN TIMBEROR CONCRETECROSSTIE ASE OF RAIL AND

LSUBBALLAST LBALLAST DEPTH

Figure 4.4.2 Ballasted Double Track, Tangent Track (Timber Crosstie)

4-36 Track Structure Design

Although wood is an insulating material, the 7x9 inches) for mounting an insulated use of the timber crosstie to protect against fastening system. stray current has proven insufficient over time. Isolating the rail from the surrounding track For additional information on timber crossties structure is an important design element that refer to Chapter 5. Determining timber must be quantified to determine the extent of crosstie spacing for transit track is discussed insulation. in Section 4.4.4.

Timber crossties are generally insulated at the base of the tie plate or fastening plate. To 4.4.3.3 Concrete Crosstie Ballasted Track insulate the fastening plate, a high-density Concrete crossties are gaining popularity in polyethylene (HDP) pad (a minimum of 12 light rail transit installations. They have been millimeters (0.5 inches) projecting on all sides shown to have lower life-cycle costs, provide of the plate) is placed between the bottom of better ride quality, and incur lower track the fastening plate and the top of the tie. To surfacing maintenance costs. protect the screw spike holding the fastening The concrete crosstie is typically insulated at plate to the tie, a special insulating the base of the running rail to protect the collar/thimble is positioned in the anchor negative return running rail from potential screw spike hole to isolate the screw spike stray currents. Concrete crosstie ballasted from the fastening plate. For additional design track consists of the rail placed in the rail seat information on timber crosstie fastenings, refer area and the tie supported by a ballast and to Chapter 5. subballast trackbed as shown in Figures 4.4.3 and 4.4.4 for single- and double-track, 4.4.3.2.2 Timber Cross&s respectively. Timber crossties have been standard for light rail transit installations for years and continue 4.4.3.3.1 Concrete Crosstie Fastening to be the standard for older established transit The success of the concrete crosstie is partly agencies. Life-cycle cost comparison of due to the introduction of elastic (spring clip) timber ties and concrete ties must be fastenings at the rail hold down location. performed using a uniform baseline, including Fastening designs have evolved to meet new all fastenings and hardware needed for each requirements for electrical isolation and to type of tie. The tie spacing for timber ties is incorporate an elastic fastening to replace the generally shorter than for concrete ties, which spike, bolt and rail anchor. contributes to this comparison. Conventional rail anchors projecting into the ballast section The insulating barrier must be at the base of will create a stray current leakage path, the rail or mounting surface to provide another issue to be considered in the analysis. electrical isolation of the rail from the Also, the material cost for timber crossties can surrounding track components. The insulating vary widely over a short period of time. That barrier consists of a base rail pad and said, many transit agencies continue to use insulators for the edges of the rail base. As timber ties with satisfactory results. shown in Figure 5.4.1 of this handbook, the rail is fully insulated from the mounting Timber crossties for a transit system should surface. be hardwood (oak, maple, birch), with a cross section of 175 x 230 millimeters (generally

4-37 Light Rail Track Design Handbook

,-SUPERELEVATION 100 (4") ILLUSTRATED / 'i TRACK .Tcnn ,, ; LJVU \38”) NOM I SUBJECT TO SITE SPECIFICS AND REWREMENTS i FOR CATENARY POLES AT SUPERELEVATIONTRACK

BETkiN BASE OF RkL !iND

-SUBBALLAST t SUBBALLAST DEPTH I- SUBGRADE BALLAST DEPTH

Figure 4.4.3 Ballasted Single Track, Curved track (Timber Crosstie)

SUPERELEVATION100 (4") ILLUSTRATED

TIMBER CR CONCRETECROSSTIE (CONCRETEILLUSTRATED)

SUBBALLAST DEPTH /SUBBALLAST LBALLAST DEPTH

Figure 4.4.4 Ballasted Double Track, Curved Track (Timber Crosstie)

4-38 Track Structure Design

The concrete crosstie design includes the guidelines assume the following typical light specific type of elastic fastening system rail transit installation data: (spring clip) with insulating rail seat pad and Rail Section 115 RE rail base insulators. The elastic clip provides Vehicle Load per 5,400 kilograms sufficient toe load to the rail base to act as the Wheel (12,000 pounds) longitudinal rail anchor, eliminating the Track Modulus conventional rail anchors used with timber - Timber Tie 17.2 N/mm* (2,500 crossties. Ibs/inch per inch of rail) - Concrete Tie 34.5 N/mm* (5,000 4.4.3.3.2 Concrete Crossties Ibs/inch per inch of The standard transit concrete crosstie is rail) generally 255 millimeters (10 inches) wide Desired Load and 2515 millimeters (99 inches) long at the Transfer to base of tie. The tie is tapered, with a 190- - Ballast ~0.45 MPa (65 psi) millimeter (7.5-inch) height at the rail seat and - Sub Grade ~0.14 MPa (20 psi) a 165-millimeter (6.5-inch) height at the center Ballast Depth 255 millimeters (10 of the tie. The ties are prestressed, precast inches) concrete produced in a factory with climate Subballast Depth 200 millimeters (8 controls for the curing process. For additional inches) information on concrete crossties refer to Tie Sizes Chapter 5. - Timber 180 x 230 x 2590 millimeters (7 x 9 x 4.4.4 Crosstie Spacing 102 inches) - Concrete 190 x 250 x 2515 Ballasted track structure design is dependent (7.5 x 10 x 99 on the vehicle wheel load, a predetermined inches) track modulus target or standard, the selected Design Calculations: rail section, the type and size of tie, and the Tie Seat Load = p a. P [Timoshenk o 19291 depths of ballast and subballast. These are where : combined to meet the criteria established by a = tie spacing (variable) AREMA for both ballast pressure and P = axle load = 107 kN (24 kips) - twice the wheel load subgrade pressure. l/A P=-& Ballasted track designs can meet or exceed ( 1 the AREMA pressure requirements by altering Timber Tie: u = track modulus the variable parameters (track modulus, tie spacing and ballast depth) as needed. As a = 17.2 N/mm* (2500 lb/inch guideline the following sample calculations per inch of rail) are provided for design of ballasted track with Concrete Tie: u = track modulus timber or concrete crossties. = 34.5 N/mm* (5000 lb/ inch per inch of rail) Design computations based on Talbot, Timoshenko, Hay formulas and other E = modulus of steel = 206,800 N/mm* (30 x 1 O6 psi)

4-39 Light Rail Track Design Handbook

I = modulus of inertia 4.4.4.1 Crosstie Spacing-Tangent/ = 27.4 x IO6 mm4 (65.9 in’) Curved Track The above calculations determine the crosstie Tie Bearing Area = tie width x tie length spacing and affect the track modulus or the vertical track stiffness. Lateral track stability Timber = 230 x 2590(9” x 102”) can also affect crosstie spacing. = 595700squaremm (918 sq. in.) Concrete =250 x 2515 (IO” x 99”) The horizontal track alignment for a light rail transit system can be far more severe than for = 628750 square mm (990 sq.in) other railway systems, such as rapid transit, commuter rail, or freight railroads. Ballasted Tie Seat Load [Hay, 9821 Ballast Load = track is far more difficult to construct and 2/3Tie Bearing Area maintain in reduced tight radius curves. Subballast Load at Tie Centerline = Special consideration should be given to Seat Load increasing lateral track stability by reducing x Tie Width , .23 Tie Bearing Area the crosstie spacing. I [Talbot 19191 Ballast Depth Lateral track stability is provided by ballast Subgrade Load at the Tie Centerline is similar friction contact along the sides and bottom of to subballast load calculation except depth the tie and by the end area of tie. The end includes ballast and subballast heights. area of the tie provides a calculated degree of lateral stability. Increasing the ballast Using the above formulas, Table 4.4.1 shoulder width beyond a 450-millimeter presents the values according to the (18-inch) limit provides no increase in stability. parameters. Reducing crosstie spacing, thereby increasing the number of ties, can increase lateral track Tie spacing can be determined from this table. stability. Timber crossties have proven to Neither the AREMA recommended maximum provide greater lateral stability than concrete ballast pressure 0.45 MPa (65 psi) nor the ties based on the theory that the ballasts maximum subgrade pressure 0.14 MPa (20 sharp edges penetrate the tie surfaces psi) should be exceeded. increasing the friction and locking the tie in position. On the other hand, the concrete tie’s are The preceding computations increased weight also provides increased representative of the calculations needed to lateral stability. design the ballasted track structure. The parameters that alter the actual design are To improve the lateral stability of concrete predetermined track modulus; type of tie crossties, some tie manufacturers have (timber or concrete); depth of ballast and developed a serrated or “scalloped” side tie subballast; and tie spacing. The challenge for surface increasing the ballasts locking the engineer is to combine these parameters capabilities. to achieve the best life-cycle costs and lowest maintenance costs. Based on the above calculations, the track designer should consider reducing the conventional crosstie spacing by 75

4-40 Table 4.4.1 Ballasted Track Design Parameters Subgade Load Ballast + Subballast Tie-Ballast Load Subballast Load Tie Tie Seat Load 230 (9”) Tie 250 (lO”)Tie 255 (IO”) Ballast 455(18") Track Modulus Spacing (mm) kN (kips) MPa (Psi) MPa (Psi) MPa (Psi) MPa (psi) 17.2 N/mm2 510(20") 50.7 (11 4) 0.127 185 n.a. n a. 0 094 13.7 0096 76 (2500 lb./in/in) p=O 00093/mm 610 (24") 60.7 (13.6) 0152 221 n.a. n a. 0113 164 0.115 9 1 (0 0237lin) 685(27") 68.2 (15.3) 0.171 249 n.a. na 0127 18.5 0.130 10.3 760(30") 75.6 (17 0) 0.189 276 n.a. n a. 0.141 20.5 0.144 11.4 810 (32") 80.6 (18.1) 0.202 29.4 n.a. n.a. 0.150 21.8 0.153 12.1

34.5Nlmm2 510 (20") 60.0 (13.5) n.a n.a. 0142 204 0.115 16.8 0.115 93 (5000 lb Win) p=O.OOll /mm 610 (24") 71 8(161) n.a n.a 0.170 243 0.138 200 0138 11.1 (0.0282h) 685(27") 80.6(181) n a. n a 0.191 27.3 0155 22.5 0155 12.5 760(30") 895(201) na n.a 0212 30.3 0172 250 0172 13.9 810 (32") 95.3 (21.4) n.a. n.a. 0.226 32.3 0.183 26.6 0.183 14.8

Note: MPa=Nlmm2

millimeters (3 inches) for track curves with ties are expensive to design, fabricate and radii less than 300 meters (1000 feet). install. They have not proven to be cost- effective in light rail applications. To improve lateral stability, especially with conventional smooth concrete ties, a tie Turnout standards vary among transit anchor can be bolted to the tie. The tie agencies. Therefore various concrete tie anchor is a blade penetrating below the tie geometric layouts and designs would be into the ballast bed providing additional lateral required to meet the requirements of each stability. Tie anchors can be attached to agency. Standardization and simplicity in tie alternate ties in the track curve. design is required to allow the transit industry to develop a uniform economical standard 4.4.5 Special Trackwork Switch Ties concrete switch tie set for various turnout sizes. The current tendency of transit agencies is to use standard timber hardwood ties for special trackwork turnout, crossover and double 4.4.5.1 Timber Switch Ties crossover arrangements for both main line The present standard for timber switch ties is and maintenance facility and storage yard hardwood, predominantly oak. Tropical installations. Transit agencies using concrete hardwood ties such as Bonzai, lecki and crossties on main line and yard installations Azobe have been introduced to the North also use timber special trackwork ties in both American railway industry with mixed locations. success.

Concrete switch ties have been developed by The reader is cautioned about using tropical the railroad industry to reduce maintenance woods. Thorough research on the specific on heavy haul freight lines. Concrete switch wood selected, and the origin of the wood, is

4-41 Light Rail Track Design Handbook recommended before a procurement is tie arrangement. Tie spacings are increased undertaken. to allow for a wider than conventional tie crib opening using a special trackwork concrete tie The standard timber switch tie is generally a approximately 250 millimeters (I 0 inches) 180- x 230-millimeter (7- x g-inch) section with wide. various lengths from 2,750 to 4,880 millimeters (9 to 16 feet). The lengths of the concrete switch ties will conform to the special trackwork layout, with a Extra long timber switch ties, up to 6,710 possible specific length for each tie location in millimeters (22 feet) and longer may be lieu of groups of specific tie lengths. The required to accommodate special trackwork design will include the requirements for locations, such as crossovers and double mounting special trackwork fastenings in crossovers where the track centers remain at switches, frogs and guard rails. The designer the standard width of 3,810 to 4,420 and/or tie manufacturer will choose between millimeters (12.5 to 14.5 feet). embedded shoulders or single rail fasteners through the remaining portions of the special Similar to a main line timber crosstie trackwork layout. installation, an insulated switch plate design may be required to protect against stray Similar to timber switch tie installations, an current leakage. Insulated switch and frog insulated special trackwork fastening may be plates are similar in design to main line timber required to control stray current on concrete crossties. The concern for stray current switch ties. Insulated switch, frog and guard control has occasionally resulted in the rail fastening plates may be similar to installation of special trackwork direct fixation conventional timber crosstie installations. fasteners on timber switch ties. However, this Standard concrete tie insulated rail fastenings application is a relatively new design concept are acceptable where individual rails are for transit agencies and is proving to be installed on the switch timber. extremely expensive. For more information on special trackwork timber and concrete switch ties refer to 4.4.5.2 Concrete Switch Ties Chapter 5 of this handbook. Concrete switch tie standard designs for special trackwork installations are evolving. The railroad industry and transit, commuter 4.4.6 Ballast and Subballast and heavy metro rail systems have been experimenting and standardizing concrete Ballast is an integral material in the support of switch ties for special trackwork. The special the track structure. The quality of the ballast trackwork concrete ties used to date include material has a direct relationship to the overall the larger size turnouts, No. 15 and 20, and performance of the track structures. high-speed turnouts. Light rail transit systems generally restrict turnout size to No. 8 or 10; The quality, size and type of ballast material therefore a minimum of design layout has used can improve the performance of the occurred to accommodate these sizes. track substructure by providing an increased strength to the track system. Standard concrete switch tie designs and layouts will be different from the timber switch

4-42 Track Structure Design

Concrete crosstie installations normally shoulder resists lateral track movement and require a higher quality ballast, a larger keeps the track from buckling when the rail is gradation of ballast, and a more restrictive in compression. Continuous welded rail selection of rock aggregate. For additional requires a 300-millimeter (12-inch) ballast information on ballast material refer to shoulder measured from the end of the tie to Chapter 5. the top of ballast shoulder slope. The top slope of the ballast shoulder should be parallel to the top of the tie. The side slope of the 4.4.6.1 Ballast Depth ballast shoulder should have a maximum The variables to be considered in establishing slope of 1:2. As mentioned in Section 4.4.4.1, the track structure section are discussed the ballast shoulder may be increased in above and listed in Table 4.4.1. Additional sharp radius curved track to provide additional variables include the track gauge, depth of tie, lateral stability. The subballast and subgrade and superelevation of track curves. Figures sections must be increased to provide 4.4.1 and 4 4.2 illustrate and quantify the sufficient support width if the ballast shoulders general desired design section for ballasted are increased. track.

The depth of ballast from the bottom of the tie 4.4.6.3 Subballast Depth and Width to the top of the subballast can be determined Subballast is the lower or base portion of the by undertaking the aforementioned ballast bed located between the base of the calculations. The depth of subballast below ballast section and the top of the road bed the ballast to the top of the subgrade can be subgrade. Subballast is generally a pit run determined from these calculations. material with smaller, well-graded crushed stone. The subballast acts as a barrier filter For tangent track, the minimum depth of separating the ballast section from the ballast is generally measured from the embankment road bed materials. It provides underside of the tie to the top of subballast at both separation and support for the ballast. the centerline of each rail. For curved superelevated track, the depth of ballast is The depth of the subballast below the ballast measured below the low rail with respect for can be determined using the preceding the top of subballast at the centerline of track calculations. The ballast and subballast are as shown in Figure 4.4.2. integral parts of the track structure. Track design considers the thickness of both in the On tangent multiple track installations, the calculations to meet AREMA minimum ballast depth is measured under the recommendations of 0.14 MPa (20 psi) rail nearest to the crown of the subballast uniform pressure transmitted to the subgrade. section as shown in Figure 4.4.3. On curved multiple track installations it is measured on The width of the subballast section is each track under the inside rail closest to determined by the width of the road bed radius point as shown in Figure 4.4.4. embankment subgrade. The subballast should extend the full width of the embankment capping the top surface. 4.4.6.2 Ballast Width The width of ballast section is determined by the rail installation and tie length. The ballast

4-43 Light Rail Track Design Handbook

The subballast layer acts as a drainage layer 4.4.7 Ballasted Track Drainage for the subgrade surface allowing water to The success of any ballasted track design flow to the embankment shoulders. depends directly on the efficiency of the ballasted track to drain well and proper The end slope of the subballast generally maintenance of the drainage system This conforms to the slope of the embankment. includes the exposed ballast and subballast bed that cast off surface runoff and the To allow for an eventual ballast slope slough designed parallel drainage system, ditch and and provide walking or flat area for track culvert piping that carry the runoff. maintenance, the subballast width should project beyond the toe of the ballast slope a Drainage of the embankment or excavated minimum of 600 millimeters (24 inches). sections is of utmost importance. Ballasted track, by the nature of its design, is To support embankment materials under susceptible to contamination from both track special trackwork installations and at-grade traffic and the surrounding environment. Dirt, road crossings, a geotextile (filter fabric) may debris and fines are either dropped or blown be used at selected locations. The track onto the trackway, contaminating the ballast designer should review supplier information section. This contamination creates a non- on geotextiles and consider the application of porous or slow draining ballast bed, which can 0.54 kilogram/m2 (16 ounce/yd2) geotextiles lead to eventual deterioration and breakdown and double layers under special trackwork of the track structure. locations. Geogrid and geoweb material may be used to stabilize and strengthen the Many conventional methods are practiced to subgrade materials below turnouts and at maintain ballasted track structure. These grade crossings. These materials augment include ballast shoulder cleaning and the function of subballast. complete track undercutting to keep the ballast bed clean to ensure it drains well.

4.4.6.4 Subgrade The subgrade is the finished embankment 4.4.8 Stray Current Protection surface of the roadbed below the sub-ballast, Requirements which supports the loads transmitted through the rails, ties, and ballast. The designer Stray current corrosion protection is a subject should analyze the subgrade to determine described more fully in Chapter 8 of this whether it has both uniform stability and the handbook. The track structure design strength to carry the expected track loadings. requires an electrical barrier to insulate the AREMA recommends that, for most soils, rail. Ballasted track generally provides this pressure on subgrade be lower than 0.14 MPa electrical barrier at the rail fastenings. An (20 psi) to maintain subgrade integrity. insulating resilient material with a specified Uniformity is important because differential bulk resistivity provides the barrier at the base settlement, rather than total settlement, leads of fastening plate on timber ties and at the rail to unsatisfactory track alignment. The use of base on concrete ties. geotextiles or geogrids between the subgrade and subballast can be advantageous under For more information on electrical barriers at some conditions. fastenings refer to Chapter 5.

4-44 Track Structure Design

4.4.9 Ballasted Special Trackwork facilities to provide for special treatments Cost-effective designs consider the type of The ballasted special trackwork portion of any vehicle involved, the soft primary suspensions transit system will require specific designs to that produce ideal levels of ground vibration match the size of the components. above 30 Hz, or the stiff primary suspensions that produce levels that peak at 22 Hz. Noise Ballasted special trackwork in contemporary and vibration control is a system problem that light rail transit systems generally consists of involves the track and the vehicle wheels and turnouts paired to act as single crossovers for trucks Familiarization with the contents of alternate main line track operations. Chapter 9 herein, along with American Public Operating requirements and alignment Transit Association (APTA) and/or Federal restrictions may dictate the installation of a Transit Administration (FTA) requirements for double crossover consisting of four turnouts wayside and groundborne noise limits, is and a crossing (diamond). Turnouts are used essential to sound designs that limit noise and at the ends of transitions from double track to vibration. single track installations as well as at junction points to alternate transit routes and accesses to sidings 4.4.11 Transit Signal Work

Turnouts in the maintenance facility and Although the design of the signal control storage yard areas are generally positioned to system will not greatly impact ballasted track develop a “ladder track” arrangement that design, it can affect specific parts of the provides access to a group of parallel tracks design. The prime example of this with specific track centers For additional interrelationship is the need for the insulated information on ballasted special trackwork joints in the running rails to accommodate design, refer to Chapter 6. train control requirements. Such joints are normally required at the extremities of interlockings, each end of station platforms, 4.4.10 Noise and Vibration grade crossings, within individual turnouts and crossovers, and at other locations to be The vehicle traveling over the track produces determined by the train control requirements. noise and vibration. The impact of this noise and vibration may become significant for The light rail transit signaling system may alignments through otherwise quiet include track circuit signal systems within neighborhoods. Track design has a ballasted track zones. Impedance bond significant effect on both noise and wheel installation requirements must be coordinated squeal, however, to be effective, the control within the track structure design. Insulated system must consider the wheel and the track joints at limits of track circuits are to be as a unit. Chapter 9 provides guidelines with opposite and within 1.2 meters (4 feet) of each respect to trackwork design for low noise and other to facilitate underground ducting and vibration and introduces various concepts in traction crossbonding. noise and vibration control. For additional information on transit signal Trackwork design can have a substantial work, refer to Chapter 10 effect upon wayside noise and vibration and should be considered early in the design of

4-45 Light Rail Track Design Handbook

4.4.12 Traction Power Runoff from the street must be directed away from the track, and the track must be Traction power requirements impact the track designed with perforated pipe drains to keep design at two specific locations: the catenary the trackbed dry. Additional stabilization of pole locations in relation to centerline of track the subgrade with geo-synthetic materials and the running rail, which is used as the may be very cost-effective in reducing track negative return for the traction power system. surfacing costs Failure to provide good The catenary poles impact the track centerline drainage will result in pumping track and distance when they are located between the broken pavements. tracks. Clearance distances pertinent to the transit vehicle as well as any other potential The use of embedded track at grade users of the track (i e., freight or track crossings is proving to be a very reliable maintenance vehicles) must be considered by crossing design. Embedded track provides a the track and catenary designers. isolation of virtually maintenance-free installation with the running rail used as the negative return proper insulating properties for the rail and a conduit is essential for both timber and relatively smooth road crossing surface for concrete crosstie ballasted track. automobiles.

For additional information on traction power Coordination with the street design is also refer to Chapter 11. necessary to match the normally crowned street cross section with the level grade crossing. 4.4.13 Grade Crossings

Track designers must develop an acceptable 4.5 DIRECT FIXATION TRACK interface wherever streets cross the light rail (BALLASTLESS OPEN TRACK) tracks at grade. Grade crossings are manufactured as prefabricated units of rubber, concrete, or wood. These prefabricated units 4.5.1 Direct Fixation Track Defined are designed to resist leakage of DC current, as well as signal current. They are designed Direct fixation track is a “ballastless” track to be easily installed and replaced during structure in which the rail is mounted on direct maintenance of the track. All grade crossings fixation fasteners that are attached to a must create a flangeway between the street concrete deck, slab, or invert. Direct fixation paving and the rail. track is the standard method of construction for tracks on aerial structures and in tunnels. Some grade crossings are created by using It is also used for construction of at-grade flangeway timbers along the rails to form the track under unusual circumstances, such as flangeway and paving the remainder of the when there is a short segment of at-grade area with asphalt. Although this style is not as track between two direct fixation bridge decks. durable as the prefabricated units, it may be quite adequate in storage and maintenance Prior to designing direct fixation track, several facilities. vehicle/track related issues must be resolved. These issues relate to the vehicle’s wheel The most critical design element of all grade gauge, wheel profile, and truck design; the crossings is adequate drainage for the track. track gauge and rail section; and the

4-46 Track Structure Design compatibility of the vehicle with the guideway 4.5.2.4 Track Modulus geometry. Acoustic concerns are also very Direct fixation track is typically much stiffer important. vertically than ballasted track. This rigidity must be attenuated if transmission of noise and vibration is to be avoided. Careful 4.5.2 Direct Fixation Track Criteria selection of an appropriate track modulus and specification of direct fixation rail fasteners To develop direct fixation track design, the with an appropriate spring rate must be made following track components and standards in accordance with Section 4.3 and Chapter 9 must be specified: of this handbook. Rail Section

Track Gauge 4.5.3 Direct Fixation Track Structure Types Guarding of curved track and restraining rail Direct fixation track construction includes the The type of direct fixation track structure following designs to be used (booted tie or a direct fixation l Encased Ties This is the original form for rail fastener type) direct fixation track, dating to the late 19th century. Timber crosstie track was If direct fixation rail fastener construction constructed in skeleton form and then the is selected, the type of fastener and bottoms of the crossties were encased in supporting structure to be employed- concrete. Because the concrete held the cementitious grout pad or concrete track rigidly to gauge, typically only every reinforced plinth. fourth or fifth tie would be a full-length crosstie. Intermediate ties would be short tie blocks that support only a single rail. 4.5.2.1 Direct Fixation Track Rail Section Such designs incorporated no specific and Track Gauge measures to control stray traction power Refer to Section 4.2 and Chapter 5 of this currents or groundborne vibrations. Handbook for determination of rail section, Except in very limited circumstances for track gauge and flangeway requirements. maintenance of existing systems, encased timber tie track is no longer 4.5.2.2 Direct Fixation Track with constructed. Restraining Rail l Cemetitious Grout Pads: This form of Refer to Section 4.2.8 to determine the direct fixation track mounts each requirements, locations, and limits for individual rail fastener on an individual guarding track with restraining rail. grout pad, thereby guaranteeing the construction tolerances in the final elevation of the concrete trackbed. The 4.5.2.3 Direct Fixation Track Fastener fasteners are held in place by anchor Refer to Chapter 5, Section 5 4 to determine bolts that are cored into the concrete the requirements for specifying direct fixation base. fasteners.

4-47 Light Rail Track Design Handbook

l Concrete Plinths: This form of direct 4.5.3.1 Cementitious Grout Pads fixation track forms rectilinear concrete Cementitious grout pad track designs include:

blocks or plinths that support several l Short cementitious grout pads of sufficient direct fixation fasteners under a single rail. width to allow for installation of the direct The plinths can vary in length and fixation fastener that is formed and poured typically support between three and six directly to the concrete deck or invert. A fasteners, although longer plinths support typical configuration is as shown at the left up to twelve fasteners. Periodic rail in Figure 4.5.1. interruptions of the plinths allow cross l Short cementitious grout pads mounted track drainage into a trough that is within a recessed opening in the concrete typically located along the track deck or invert, as shown at the right rail in centerline. Figure 4.51. l Ballastless Booted Tie Blocks: This form of direct fixation track is an updated Grout pads typically support only a single version of the encased tie design. It fastener, although current practice is to build typically incorporates two block concrete longer pads to support at least four fasteners. crossties that have an elastomeric “boot” The longer design provides improved integrity on the bottom of each tie that provides of the pads and ease of maintenance if a electrical and acoustic isolation between fastener is replaced or repositioned. the ties and the encasing concrete. As with the earlier design, most ties would be 4.5.3.1.1 Cementitious Grout Pad on single blocks with no crosstie member Concrete Surface between the rails. The short cementitious grout pad design acts as a leveling course between the underside of Variations of the above designs can be found, the direct fixation fastener and the concrete such as direct fixation rail fasteners bolted deck or invert surface. The anchor bolt directly to structural steel bridge members. inserts are set in the deck slab to provide the Such arrangements are generally in response structural integrity of the fasteners. to a site-specific design issue and will not be addressed in this handbook.

DIRECTFIXAnON FASTENER OlRECTFlXAiW F WTH OR WTHCUT CANT WHORWITHCUTCAN MtCHMI EaT INSERT ANcnoR 8aT INSERT

Figure 4.5.1 Cementitious Grout Pad Design-Direct Fixation Track

4-48 Track Structure Design

This design requires core drilling of the 4.5.3.1.2 Cementitious Grout Pad in concrete invert to grout the anchor bolt in Concrete Recess place The drilling can be undertaken either Some transit systems have experienced grout prior to or after grout pad installation. The bolt pad delamination, because cementitious grout assemblies are permanently anchored with an pads have a tendency to curl or pull away epoxy grout material. from the parent concrete deck or invert during curing and aging. It is possible to achieve The cementitious grout pad can be formed better bonding with less likelihood of such and poured before the rail fastener is placed; failures by forming the grout pad within however it may be difficult to achieve an recesses in the concrete invert. The recessed absolutely level and true top surface for the design provides additional deck or invert rail fastener. If the grout pad is slightly too bonding by locking the four sides of the pad. high, grinding may be required. If it is too low, it may be necessary to place metallic or The anchor bolt assembly drilling can be elastomeric shims beneath the rail fasteners. undertaken either prior to or after grout pad installation. Prior drilling is recommended as Alternatively the assembled rail and rail it results in less disturbance to the bond of the fasteners can be suspended at proper grade cast-in-place grout pad. and alignment above the concrete invert and the grout either pumped or =dry packed” under 4.5.3.1.3 Cementitious Grout Material the rail fastener. If this approach, known as The selection of a cementitious grout material “top down” installation, is taken, it is essential must be undertaken carefully. The use of to ensure that the grout does not enter the incompatible special epoxy grouts, bonding recesses on the bottom surface of the direct agents and additives can result in pad fixation rail fastener which could compromise delamination and cracking. The material the rail fastener spring rate. This can be should be compatible with the deck or invert avoided by placing a minimum of one shim concrete and have similar thermal expansion beneath the direct fixation rail fastener before characteristics. It must also be compatible grout placement. It is also necessary to lift the with the service environment of the trackway. rail and fasteners after the grout has cured to locate and fill in any voids or “honeycomb” in Large inaccuracies in the elevation of the the top surface of the grout pad that are concrete invert and track superelevation can caused by trapped air or improper grout result in both very thin and very thick grout placement. pads. Both can be troublesome but thin pads are particularly prone to early failure. Grout pads typically depend on the strength of Cementitious grout pads that are less than 38 the bond between the concrete invert and the millimeters (1.5 inches) thick are generally grout for their stability. Reinforcing steel more susceptible to fracture. typically cannot be used because the pad is so thin. The concrete invert is typically As a guideline, although the cementitious roughened before grout placement and epoxy grout pad design has and is currently used on bonding agents can be used to enhance the some transit systems, it is not recommended bond between the grout and the concrete. due to the design’s history of pad failure. Cementitious grout pads tend to delaminate and break down, requiring high maintenance,

4-49 Light Rail Track Design Handbook

particularly in colder climates subjected to l Concrete plinths of sufficient width and freeze-thaw cycles. Locations with minimal height for installation of a direct fixation clearance requiring a low-profile direct fixation fastener within a recessed opening in the track structure may be the best application of concrete deck or invert, as shown at the the cementitious grout pad system. right rail in Figure 4.5.2.

4.5.3.2.1.1 Concrete Plinth on Concrete 4.5.3.2 Reinforced Concrete Plinth Surface. The concrete plinth width and height The recommended direct fixation track design must be sufficient to accept the full length of is the raised reinforced concrete plinth the fastener and anchor bolt assembly. It system. The reinforced concrete plinths used must also accommodate the reinforcing steel for direct fixation track include various designs that is required to confine the concrete mass to suit tangent track, curved track, that supports the direct fixation rail fastener superelevated track, and guarded track with and anchor bolt insert. restraining rail. The designs affect the lengths and shapes of the plinths and the reinforcing The concrete plinth is connected to the deck bar configurations as follows. or invert concrete surface with a series of stirrups or dowels protruding from the deck or invert. Additional plinth reinforcing steel is 4.5.3.2.1 Concrete Plinth in Tangent Track connected to and supported by these stirrups Concrete plinth in tangent track generally or dowels. consists of two designs: l Concrete plinths of sufficient width and The anchor bolt inserts may be installed by height for mounting of the direct fixation the cast-in-place method or drilled and epoxy fastener directly to the concrete deck or grouted in place. Cast-in-place installation is invert, as shown at the left rail in Figure recommended as it results in less disturbance 4.5.2. to the plinth and eliminates any possible

TRAC% GAUGE1435 (4’-6 l/2’) C RAIL k FASTENER 4 di i i i -115 IKERUNNING RAIL LATERALAIJ&STWENT PROMOEDAT 71%’ DIA. ANOlOR BOLT LOCAlWi t 6 (l/47 RAIL H&O-DOW ASSEH6l.Y DIRIC;;yoN FASTENER

mnuu SHIM 3 (l/6-) Ilax WIN PLMiH CONCRETE

STRUCNRE SLAB

38 (I t/z’) aumcf - 3 soEs ROUGMENTOP OF SLAB PRIOR TO RACING PUNlH #5 BARS 0 254 FCR 762 CTRS CONC APPLY BONDINGAGENT

‘A- DINENSON TO BE ESTABJSHED USING COUPONENTHEIGHTS AND TYPE CF GKUT PAB lNSTALLATlONAT SURFACE OR RECESSED

Figure 4.5.2 Concrete Plinth Design -Tangent Direct Fixation Track

4-50 Track Structure Design problems with drilling through reinforcing construction contractor for setting the height of steel. It also eliminates the extra work and the plinth formwork so that the required potential problems of dealing with the epoxy superelevation is achieved. In addition, care grout materials used in the core drilling must be taken to ensure that the rotation of method. the concrete plinth at the low rail leaves sufficient room for the anchor insert assembly 4.5.3.2.1.2 Concrete Plinth in Concrete Recess. Similar to the grout pad method, the The plinth height is established by the concrete plinth design has a variant wherein elevation of the low inside rail of the curved the second pour concrete can be recessed track as shown in Figure 4.5.3. Applying the into a trough in the base concrete slab. The profile grade elevation at the low rail of the recessed design allows a reduced plinth curve, the superelevation is established by height above the deck or inverts and provides rotating the top of rail plane about the gauge additional deck or invert bonding by locking in corner of the low rail. The addition of the four sides of the plinth. superelevation alters the cross slope and thickness of the concrete plinths so that the The recessed design obviously requires that a typical section is no longer symmetrical. trough be formed in the trackway invert, an additional work activity and hence expense to The embedment of the field side anchor bolt the contractor building the trackway. The insert of the low rail fastener establishes the extra cost associated with forming the trough height of the plinths, The reinforcing bar is not insignificant and designers should requirements and configurations depend on carefully weigh the costs and benefits of the the plinth heights. recessed design before deciding on a preferred method. The trough may also Plinth or second-pour concrete direct fixation compromise the structural integrity of the base track can be mounted either directly to the slab, particularly on aerial structures, so the surface or the recessed opening in the design must be coordinated with the structural concrete deck or invert. The latter design team. arrangement can be particularly advantageous in superelevated curved track Some designers object to the placement of since it can substantially reduce the plinth the plinths directly on the concrete base height at the high rail. because it places the top of rail elevation about 360 millimeters (14 inches) above the 4.5.3.2.3 Concrete Plinth in Guarded Track invert. In the event of a derailment, where the with Restraining Rail or Safety Guard Rail wheels do not end up on top of the plinths, The use of either a restraining rail or a safety substantial damage to the underside of the rail guard rail in direct fixation track will require vehicle could result. The placement of the that the concrete plinths be wider than normal. plinths in a recess minimizes this concern. Figure 4.5.4 illustrates a typical plinth for use with restraining rail. A similar arrangement is 4.5.3.2.2 Concrete Plinth on Curved Track required for a safety guard rail system. This Concrete plinth design for curved track must concrete plinth arrangement can be either consider track superelevation. The track mounted directly to the surface or the designer must provide guidance to the recessed opening in the concrete deck or invert.

4-51 Light Rail Track Design Handbook

l- oi SJPERfLEVAnONTAG TO BE 1. XNL dl .- .--- , - ECMED ON TOP OF PLINTH TRACKCAL& 1435 ((‘-6 ,,2-j I FASTENER DIA. Ah’CHPRBOLL (APPROXINATELOCATION) --\ LOCATION-6 (1/4 ) 1 -II I ,-SUPERELEVATION RAILHOLO-DOW I ASSEMBLY ~~c;A~.4ncti FASTENER /- ,-‘XRlICAl MY : i (l/8’) mm OR INSERT

-VARIES 152 (67 MN (T?P)

. STRUCTURESt~f 3 (1 l/Z’) CLEARANCE- 3 SDES BARS0 330 (IS) FOR 666 (2f) CTRS 0 254 (lo-) FOR 762 (30’) CTRS

+ PU - PRWlLE GRACi LINE SUB SnRRUPS PRlCRTO PtAQNt FUNTH TYPICAL KW&EIL #‘FLY BCNOING ‘A- LMlENSONTO BE ESTABLlSiED U~NG COMPONENTHEIGHTS Am lWf OF F’LINTHINSTALLAnON AT SURFACECR RECESSED Figure 4.5.3 Concrete Plinth Design-Curved Superelevated Direct Fixation Track

.~C_,..-...l.” ..-. _.” r$LG.dnn lur BRAMETASSEMBLY 6 115 RE RUNNINGRAlL TRACX 7/ LAmAL AOJJSTNENT

PMlH PimE PARULEL TO TOP ff RfiL PLANE WEN FASTENERCOHSAJNS CANT RAJt HCUMJO~N ASXNBY OLlLC~~XA~~ FASTENERMM C%? FASTENER!iDMT kfmw 5uu 3 w63 micx EMEWE ANCHORINSERT

3 9DES REINFCKINGEARS

2x) (9‘) cm) EUBEGEOANMOR NSERK RESKWNINCRflL ERACKET

Figure 4.5.4 Concrete Plinth Design-Curved Superelevated Guarded Direct Fixation Track with Restraining Rail

4.5.3.2.4 Concrete Plinth Lengths in curved track is curved or chorded, and the Concrete plinths can be formed in various locations of construction joints and expansion lengths. Typical plinths of intermediate joints in the invert. Concrete plinths in curved lengths will accommodate three to six direct track are generally constructed in short fixation fasteners between drainage chases as tangent segments for ease of formwork. shown in Figure 4.5.5. Concrete plinth lengths are affected by differential shrinkage of structure and plinth, Concrete plinth lengths are dependent on local climate conditions and temperature several track design factors: whether the ranges. track is tangent or curved, whether formwork

4-52 Track Structure Design

685 I + 127”) ! FASTENERS AT

I i ‘PI INTH GAP / i I I .- I / I I n ! n i

LBRACKET AND i EDGE OF KEYWAYI U69 RAIL REMOVED FILLED BETWEEN FOR CLARITY PLINTHS

TYPICALLAYOUT W-H RESTRAlNlNGRAIL

20 (0.7874”) OFFSETS

Ll”34’ 04” / o”47’ 02” PLINTH INSTALLATION BY CHORD METHOD (25 & 150 METER RADII)

Figure 4.5.5 Concrete Plinth Lengths

4-53 Light Rail Track Design Handbook

4.5.3.2.5 Concrete Plinth Height longitudinal structure slippage, where zero toe The heights of the rail section and the direct load is the fastener design and the rail and fixation fastener and the length of the anchor structure are thermally independent. bolt insert must be determined to establish the height of the concrete plinth.The track 4.5.3.2.7 Concrete Plinth Reinforcing Bar structure deck slab or invert slope should Design generally slope at I:40 towards the centerline The plinth reinforcement begins with the of track. On curved track, the structure itself construction of the trackway invert. A series may be superelevated and parallel to the of stirrups or dowels is placed longitudinally in eventual top of rail plane. In addition, the the concrete plinth, positioned to clear the longitudinal surface drainage gradient is embedded anchor bolt inserts and the ends of critical to provide adequate drainage of the plinth openings or gaps. The stirrups should trackbed. protrude a minimum distance of 75 millimeters (3 inches) from the deck or invert to allow both The key dimension to establishing the plinth the transverse reinforcing steel and the plinth height is dimension “A” shown in Figure 4.5.3 concrete to lock under the stirrups. The from the top of rail plane to the intersection of stirrup height must be designed to suit the the deck or invert slopes at the track eventual concrete plinth height and centerline. reinforcement design.

The plinth heights should be kept to a Different contractors often construct the bridge minimum to enhance structural stability, deck or trackway invert and the track. The especially if the deck or invert is relatively invert contractor is normally responsible for level and the track alignment requires 100 to the proper placement of the stirrup reinforcing 150 millimeters (4 to 6 inches) of steel that projects from the base concrete. superelevation at the outside rail. This reinforcing steel must be properly installed and protected from damage after 4.5.3.2.6 Direct Fixation Vertical Tolerances installation. The wheels of construction The height of the direct fixation fastener is equipment often damage stirrups. The use of critical to vehicle ride quality and interaction the recessed plinths may help mitigate this between rail and track structure. To achieve a problem. near-perfect track surface longitudinally, the use of shims between the top of plinth and the The plinth reinforcement that is installed by base of direct fixation fastener is often the trackwork constructor consists of a series implemented. The maximum difference in of “J” hook bars and longitudinal bars. A elevation between adjacent fasteners should transverse collector bar is sometimes placed be less then I-112 millimeters (1116 inch), the at the ends of each concrete plinth for stray thinnest shim thickness. Shims generally current control as shown in Figure 4.5.6. range in thickness to 12 millimeters (I/2 inch) to compensate for either inferior construction The design size of the concrete plinth or eventual structure settlement. Fastener determines the size and outline of the “J” shim thicknesses above the 12-millimeter hooks and the length of the longitudinal bars. range exist and special anchor bolt lengths Tangent track will require a constant height to are then required. Fasteners installed out of conform to the general height of the concrete longitudinal surface by more than I-112 plinth Curved track alignments with millimeters have been known to hinder superelevation will require various sizes and

4-54 Track Structure Desian

1520 (60”) ,-DIRECT FIXATlON FASTENERS

255 760 (30”) 760 (30’) 255 , 250 , 255 380 LATERAL REINFORCING ‘J” FASTENER SPACING BAR HOOPS 0~‘) , 380 (lo-,-l (9 8”) 1 (10”) (15’) DECK OR INVERT REINFORCING BAR STIRRUPS (SEE NOTE 2)

ONCRETE PLINTH

NGITUDINAL BARS

MLD LOCATION (TYP ) STIRRUP S?ACING 1 508 (20”) 1 508 (20”) 1 508 (20”) ON TRANSVERSE COLLECTOR I I BARS (SEE NOTE 3) 3 FASTENERPLINTH LAYOUT

TRANSVERSE COLLECTOR BAR 38 (1.5”) MIN AT EACH END OF PLINTH TO BE WELDED TO THE FOUR LONGITUDINAL BARS (SEE NOTE 3) ANCHOR BOLT INSERT (TYP ) \ c RAIL

LLONGITUDINAL BARS

RANSMRSE “J’ HOOPS DECK STIRRUPS f 0 BE WELDED TO INSIDE ONGITUDINAL BAR SECTIONA LONGITUDINAL BAR

DECK 0 IR INVERT STIRRUPS WELDS (TYP.) 91 / 1-38 (i 5”) MN : CONCRETE COVER

Ih PRE INSTALLED DECK OR INVERT PLAN vlEW STIRRUPS TRANSVERSECOLLECTOR BAR NOTES:

1 ON CURVES OF LESS THAN 240m RADIUS. MAXMUM PLINTH LENGTH if FOUR FASTENERS

2 DECK OR INVERT REINFORCING BAR STIRRUPS PRE-INSTALLED

3 ELIMINATE WELDS AND ~RANSMRSE COLLECTOR BARS IF EPOXY-COATED REINFORCING BARS ARE USED

Figure 4.5.6 Concrete Plinth Reinforcing Bar Design shapes of reinforcing bar “J” hooks as shown 20-millimeter (0.75inch) clearance at the in Figure 4.5.6. Design size of reinforcing fastener anchor bolt inserts. bars and stirrup locations must include the requirements of providing 38 millimeters (1.5 The reinforcing bar network must be inches) minimum of concrete cover from the continuous to control stray current corrosion edge of bar to the face of the concrete and a within the direct fixation track system. The aerial deck, at-grade slab, or tunnel invert

4-55 Light Rail Track Design Handbook reinforcing bar system must be continuous base concrete causing corrosion of the and connected to a negative ground system. stirrups. In tunnels that do not have adequate A similar continuous network must be means of leak control, the potential of surface established and connected to a negative water penetrating the separation point may be ground system through the deck or slab unavoidable, leading to reinforcing bar rusting reinforcing system to provide similar and corrosion. Various sealants, such as protection to the second pour concrete plinth epoxies, have been used to attempt to seal reinforcing bar system. this joint but virtually every product available will eventually dry out, harden and peel away. The concrete plinth reinforcing bar system can The use of a sealant can actually exacerbate be made electrically continuous by the a seepage condition by trapping water following methods: beneath the plinth concrete. As a guideline, l The deck or invert stirrups installed during sealants are discouraged and the use of the initial construction must be connected epoxy-coated reinforcing steel for stirrups is (welded) to the deck or invert reinforcing recommended. bar network.

l The concrete plinth reinforcing bar system 4.5.3.3 Direct Fixation Fastener Details at must be completely connected (welded) to the Rail the protruding deck or invert stirrups. Typically, the track system will have the rail

l When the stirrups or dowels are not positioned with a cant of 1:40 toward the track connected (welded) to the deck or invert centerline. Rail cant in direct fixation track reinforcing bar system, then the concrete may be achieved by several methods:

plinth reinforcing bar network must be l The top surface of the concrete plinth or completely connected (welded) and grout pad can be sloped to match the connected to a negative ground system. required cant. In such cases, the direct This requires connections between each fixation fail fastener itself would be flat, plinth at the concrete plinth openings or with no built-in cant. gaps. l The plinth concrete or grout pad can be

l The use of epoxy-coated reinforcing bars poured level (or parallel with the top of in the stirrups and the concrete plinth rails in superelevated track) and the rail reinforcing bar network provide the fasteners can be manufactured with the required stray current corrosion desired cant built into the rail seat of the protection. Care must be exercised fastener. during construction to retain complete protective epoxy coating coverage on the Both methods can produce acceptable results. stirrups and concrete plinth reinforcing bar Placing the cant in the rail seat of the fastener network. Chipped or damaged epoxy simplifies the construction of plinth formwork coating must be covered in an acceptable and better ensures that the desired cant will protective paint compatible with the initial actually be achieved, particularly when epoxy coating material recommended by bottom-up construction is anticipated. If top- the epoxy coating manufacturer. down construction is used, rail cant can be reliably achieved in the concrete if the jigs In some cases, surface water can penetrate used to support the assembled rails and rail the joint between the plinth concrete and the fasteners incorporate cant adjustment

4-56 Track Structure Desian capability. If canted fasteners are used, it The individual tie blocks support the rail. may still be necessary to procure flat Microcellular elastomeric pads support the fasteners for use in special trackwork areas. blocks. The pads and tie blocks are enclosed in a rubber boot before installation. Lateral adjustment capability and fastener anchor bolt locations are important elements The microcellular pad provides most of the in the design and configuration of direct tracks elasticity. A rail pad also provides fixation rail fasteners. The rail cant location some cushioning of impact loads, although it must be considered when positioning was found that improper rail pad design could embedded anchors. Rail cant at the base of act in resonance with the underlying rail or at the top of the concrete alters the microcellular pad to create excessive rail anchor positions (refer to Figure 4.5.7). corrugation. Excessive shimming on a canted concrete surface may tilt the rail head closer to the When properly designed, LVT can be center of track, which impacts track gauge. engineered to provide whatever track modulus For additional information on direct fixation or spring rate is required by changing the fasteners, see Chapter 5. composition or thickness of the microcellular pad. The most common application has a spring rate in the range of 15,760 to 24,500 4.5.3.4 Direct Fixation “Ballastless” N/mm (90,000 to 140,000 lb/in) to provide Concrete Tie Block Track [31 maximum environmental benefits. Conventional construction for direct fixation track includes the installation of either LVT, and most encased tie systems, reduce cementitious grout and concrete plinths with the need for reinforcing steel. LVT does not elastomeric rail fasteners or encased require a reinforced invert, which often makes monoblock ties in a concrete embedment as this system more competitive with a plinth shown in Figure 4.5.8. One alternative to the type of installation. fastener-on-plinth system to provide a “softer’ track is the Low Vibration Track (LVT) shown The installation of LVT-and almost all on Figure 4.5.9. Versions of this type of encased tie systems-requires “top-down” installation and its predecessors date back to construction, where the rail is suspended from the mid-1960s. It is marketed as a direct temporary supports, with ties and rail equivalent to the elastomeric rail fastener. fasteners attached, at the final profile elevation. The encasement concrete is then Although not new technology, the LVT is poured into the tunnel invert around the track. relatively new to the transit industry. Earlier When the concrete is cured, the supports are versions of this type of dual-block concrete tie removed. An undesirable feature of LVT track trackwork incorporated a steel angle gauge design is the rail’s lack of lateral adjustment bar between the concrete blocks. The LVT capability once the track is in place. design does not incorporate the gauge bars, since the concrete encasement holds gauge.

4-57 Light Rail Track Design Handbook

$ RAIL SEAT MOUNTING 4 RAIL AT THE TOP OF PLINTH I $ RAIL SEAT MEASURED AT BASE OF RAlL $ RAIL MEASURED AT GAUGE LINE B 751.80 (29.5484”)

115 Ri RAiL HEAD

C TO (2 TRACK-

t TOP OF CONCRETE FASTENER L PLINTH HEIGHT VARIES i DTO~TRACK- . CHART FOR CANT 1:40

OF&T CANT ;S$3LILIEO AT CANT EST&IMED AT c HEAD - Q MOUNTING TOP Cf CONCRETE 0 152.35 3.81 (0.1500”) 755.61 (29.7484’) 755.61 (29.7484') is.05 (3/4') 171.40 1 4.29 (0.1689') 755.61 (29.7484-l i 7.S6.09._-.-- 129.7673-J_-. - 25.40 (1') 177.75 4.44 (0.1748.) 755.61 (29.748~ k') 1 756.24 (29.7732') 1 31.75 (1 l/4') 184.10 4.60 (0.1811') 755.61 (29.7481 1') 1 756.40 (29.7795") .38tn--. . " fl, l/73_, - , I) 19045__. .- 4.76.--- (0.1874-b\---- I I 75561" ". " (3974sr" - . - 1') 756.56 (297858') 44.45 (I 3/4') 1 196.80 4.92 (0.1937') 1 755.61 (29.7484') 756.72 (29.7921') 50.80 (2') 203.15 “.I.%na ,“.-““Tm 7imA"\ , I 7Wfil. “W.1. m715Lq\...... - 765.89 (29.7988.) 57.15 (2 t/4-1 I 209.M ,'I 757.04 129.80477 --- - \- , a , 524 (42063') 1 755.61 (29.748r kT5n 13 l/7'\ I 09 74aI .“... \. ., - , 71585“.“.“” I 540-..- fO7176'1\----- I I, 7~5.61__~__ ,.-.. .-k-j 1 757.20 i298uo.j J

CHART FOR CANT 1:20

RAIL + :A~KNER CANT ~S$-~t-E~ AT CANT ESThHED AT 1 ?lzER HEIGHT 1~;f-?t~NG TOP OF CONCRETE 152.35

171.40 &7“.. (0.3374')

}rso5(3/0"".." ,. , 177.75 t , -.198.8 (0.3499') 1 :

31 75 f1 l/A’\ 1 18410.” . . . . 1 9.20 (0.3624') 75947 ma984 “.-*I ,. ., I , , 1t 38.10--.-. I1 l/Z’)1-1 I 190.45 I 9.52 (0.3749') : 44.45 (1 3/4') 196.80 } 9.84 (0.3874.) : 50.80 (2') 203.15 f 10.16 (0.3999') " : 57.15 (2 l/4') 209.50 1 IO.48 (0.4124') : -.~ - ,-~ ( 63.5'3 (2 l/2") 21585 1 10.79 (0.4249') 759.42 (29.; 6984") 1 76259 (30.0232-j

Figure 4.5.7 Rail Can? and Base of Rail Positioning

4-58 Track Structure Design

c TIE & TRACK I I

IRON SHOULDER

I I MAXIMUM LEVEL OF ENCASEMENT CONCRETE 150 (59’) FROM BOTTOM OF TIE

Figure 4.5.8 Encased Concrete Crosstie

$ TRACK

1435 (4--B l/Z’): TRACK GAUGE CONCRETE BLOCK MICROCELLULAR

50 (2”) MINIMUM MAXIMUM LEVEL OF ENCASEMENT ENCASEMENT CONCRETE 150 (5 9’) FROM BOOT BASE CONCRETE UNDER BOOT J

Figure 4.5.9 Standard LVT System Encased tie systems vary widely in cost, but Direct fixation track built on a bridge structure can usually be installed quite rapidly, will obviously not have to directly contend with compared to plinth type systems. LVT block any subsurface drainage issues. Direct replacements are feasible on a small scale, fixation track constructed at-grade or in a consisting of a slightly smaller block grouted tunnel, on the other hand, must be properly in the cavity of a removed tie block. drained beneath the track slab. Standard underdrain details, similar to those used in highway design, must be provided to keep 4.5.4 Direct Fixation Track Drainage groundwater out of the under-track area. The successful direct fixation track will include an Drainage is as important to the success of a efficient surface drainage system. Experience direct fixation track installation as it is to any has shown that foresight in the design of other type of track structure. This includes surface drainage for the direct fixation track both drainage of water from the top surface of structure is required to avoid accumulation of the track and the subsurface support system. standing water or trapped water pockets.

4-59 Light Rail Track Design Handbook

At the interface of ballasted track to direct 4.5.6 Direct Fixation Special Trackwork fixation track, the direct fixation track system should include. The direct fixation special trackwork portion of l Protection for adjacent ballasted track any transit system will require special segments; the direct fixation track surface treatment and a different concrete plinth runoff should be directed away from the design than main line direct fixation track. ballasted track. The supporting plinths or track slabs require detailed layout, as well as coordination with l A transverse drainage chase or diverting the signal and electric traction design of the wall directing surface runoff to the fasteners, switch rods, and gauge plates. drainage system in lieu of runoff into the ballasted track area. Direct fixation special trackwork in l Concrete plinths that do not butt up to the contemporary light rail transit systems ballast wall retainer or drainage diverting generally consists of turnouts grouped to act wall Lateral drainage chases between as single crossovers for alternate track the last plinth face and the ballast wall operations. Operating requirements may retainer are essential. dictate the installation of a double crossover with four turnouts and a crossing (diamond). The design positioning of deck surface Using double crossovers in tunnels and on drainage scuppers must consider the rotation bridges may incur higher track costs, but may of the deck or invert due to superelevation. be very economical in providing structural cost savings.

4.55 Stray Current Protection Requirements 4.5.7 Noise and Vibration

The track structure design requires an The vehicle traveling over the direct fixation electrical barrier at the rail. Direct fixation track produces noise and vibration. The track generally provides this electrical barrier impact of this noise and vibration generally within the direct fixation fastener body. An becomes significant on alignments through insulating resilient material with a specified sensitive areas, such as near hospitals. Track bulk resistivity forms the elastomeric and design has a significant effect on both noise insulating portion of the fastener. The coating and wheel squeal, and the designer must of the rail with an epoxy insulating material consider the wheels, trucks, and the track as should be considered in areas of extensive one integrated system. Chapter 9 provides tunnel seepage or perpetual dampness. guidelines with respect to trackwork design for low noise and vibration and introduces various The electrical barrier for the low vibration concepts in noise and vibration control. encased tie direct fixation track system is provided at the rail base. Similar to concrete Trackwork design can have a substantial tie fastenings, the electrical barrier is effect upon wayside noise and vibration. established by an insulated resilient rail seat Noise and vibration should be considered pad and spring clip insulators. early in facilities design to provide for special treatments. Cost-effective designs consider For more information on electrical barriers on the type of vehicle involved, the soft primary direct fixation fasteners, see Chapter 5. suspensions that produce ideal levels of

4-60 Track Structure Design ground vibration above 30 Hz, or the stiff fixation track centerline distance and aerial primary suspensions that produce levels that structure width when they are located peak at 22 Hz. See Chapter 9 of this between the tracks. Clearance distances handbook. pertinent to the transit vehicle and any other potential users (i.e., track maintenance vehicles) are a design issue that must be 4.5.8 Transit Signal Work considered by the track and catenary designers together. Isolation of the running Although design of the signal control system rail, when used as a negative return conduit, will not greatly impact direct fixation track is essential and a specific resistivity in the design, it can affect specific parts of the elastomer is a key design issue. design. The prime example of this interrelationship is the need for insulated For additional information on traction power joints in the running rails to accommodate refer to Chapter ? I. train control requirements. Such joints are normally required at the extremities of interlockings, each end of station platforms, 4.6 EMBEDDED TRACK DESIGN within individual turnouts and crossovers, and at other locations to be determined by the Embedded track is perhaps the single most train control design. distinguishing characteristic-the signature track-of a light rail transit system in a central The light rail transit signaling system may business district. Deceptively simple in include track circuit signal systems within the appearance, it is arguably the most difficult direct fixation track zones. Impedance bond and expensive type of transit track to installation requirements must be coordinated successfully design and construct. In addition with concrete plinth track structure design. to typical structural design issues that affect Insulated joints at the limits of the track any track, embedded track design must also circuits must be opposite and within 1.2 address difficult questions with respect to meters (4 feet) of each other to facilitate electrical isolation, acoustic attenuation, and underground ducting and traction urban design, all in an environment that does crossbonding. Reinforcing bars in the not facilitate easy maintenance. The “correct concrete may prevent track circuits from design” may be different for just about every operating reliably. transit system. Even within a particular system, it may be prudent to implement two or For additional information on transit signal more embedded track designs tailored to site- work, refer to Chapter 10. specific circumstances.

4.59 Traction Power 4.6.1 Embedded Track Defined

Traction power requirements impact the track Embedded track can be described as a track design at two specific locations: the catenary structure that is completely covered-except pole locations in relation to the track for the top of the rails-within pavement. centerline and the running rail, which is used Flangeways can be provided either by using as the negative return for the traction power grooved head girder rail or by forming a system. The catenary poles impact the direct flangeway in the embedment material.

4-61 Light Rail Track Design Handbook

Embedded track is generally the standard for detailed if the track system is to be functional light rail transit routes constructed within and have minimal long-term maintenance public streets, pedestrian/transit malls, or any requirements. area where rubber-tired traffic must operate. On several transit systems, both highway Traditional street railway/tramway systems grade crossings and tracks constructed in used wheels with relatively narrow tread highway medians have used embedded track. surfaces and narrow wheel flanges. The chief reason for this was to ensure minimal Embedded track can be constructed to projection of the wheel tread beyond the rail various designs, depending on the head where it could contact the adjoining requirements of the system. Some embedded pavement, damaging both the wheel and the track designs are very rigid while others are pavement. Such wheels had tread widths as quite resilient. narrow as 50 millimeters (2 inches) and overall wheel widths of only 75 millimeters (3 Prior to developing an embedded track inches) Problems with these wheels, design, several vehicle/track related issues particularly in the vicinity of special trackwork, must be resolved, including vehicle wheel resulted in most systems adopting wheels with gauge, wheel profile, and truck design; the much wider treads. track gauge and rail section; and ability of the vehicle to negotiate the track in a satisfactory Wheels with an overall width of 133 manner. millimeters (5.25 inches) are common on new start systems. Increasing the wheel tread width beyond the rail head introduces an 4.6.2 Embedded Rail and Flangeway overhang with potential for interference Standards between the outer edge of the wheel and the embedment materials. To avoid wheel or To develop embedded track designs, the pavement damage, either the rail head must following track components and standards be raised above the surrounding embedment must be specified: material or the pavement immediately l Rail section to be used: girder groove adjacent to the rail must be depressed as (guard) rail or tee rail shown in Figure 4.6.1. l Track gauge in the embedded section l Flangeway width provided in girder rail or Other factors must be considered when formed section positioning the rail head with respect to the l Guarding of flangeways in curved track pavement surface. In resilient embedded and restraining rail track design, a rail head vertical deflection ranging from 1.5 to 4 millimeters (0.060 to Refer to Section 4.2 and Chapter 5 to 0.160 inches) must be considered. In determine rail section, track gauge and embedded track, eventual vertical rail head flangeway requirements. wear of 10 millimeters (0.39 inches) or more must be accommodated. In addition, the 4.6.2.1 Embedded Details at the Rail Head wheel tread surface will wear and can result in The rail section and wheel profile used on a a 3-millimeter (0.12-inch) or greater false transit system must be compatible. Further, flange height. Over the life of the installation, the rail installation method must be carefully the total required vertical displacement

4-62 Track Structure Desian

IRANST WHEELMDTHS policies must include a regular wheel truing program.

When rail head wear has eliminated approximately half of the projecting 6 millimeter (0.12-inch) vertical head clearance, the original projecting dimension can be RAILHEAD ASOK S”RRO”NMNG EMBEWENT restored by production grinding of the embedment material.

TOP OF RAIL POSITIONED ABOVE EMBEDMENTSURFACE 4.6.2.2 Wheel/Rail Embedment Interference TRANSITWEEL MDT% The width of a light rail vehicle wheel is a major design issue. Each design option has certain drawbacks such as:

l Wide wheels increase the weight (mass) on the unsprung portion of the truck and project beyond the field side of the head R*IL HEADABOK of most rail designs. Wide wheels are therefore susceptible to developing hollow treads and false flanges and could require TOPOF RAIL PO&IONED more frequent wheel truing to maintain AT EMBEDMENTSURf ACE acceptable tracking through special trackwork. Figure 4.6.1 Embedded Rail Head Details

l Narrow wheels result in limited tread between the rail head and the pavement support at open flangeways and increase surface immediately adjacent to the rails could the possibility of wide gauge derailments. exceed 15 millimeters (0.59 inches). This typically forces the adoption of either A 15millimeter (0.59-inch) projection of the flange-bearing special trackwork or the rail above the pavement would be excessive use of movable point frogs. for an initial installation. Such a rail projection l Medium wheels partially reconcile the could hinder snow plowing operations at problems noted above, but introduce the grade crossings and could be hazardous in possibility of undesirable wheel tread vehicle and pedestrian areas. A 6-millimeter protrusion beyond the field side of narrow (0.24-inch) protrusion is recommended for rail head designs. They also provide initial installation, which should accommodate limited tread support in special trackwork resilient vertical deflection, some initial vertical and may require flange-bearing special rail head wear, and a moderate amount of trackwork or movable point frogs. false flange wheel wear. As stated in Section 4.6.2.1, embedded track False flanges should not be allowed to design must consider the surrounding progress, especially to the 3-millimeter (0.12 embedment material’s exposure to the inch) height, and the track designer should overhanging or protruding wheel treads. stress that the vehicle system maintenance

4-63 Light Rail Track Design Handbook

The following table summarizes head widths positioned below 6 millimeters (0.25 inches) is of typical girder rail and tee rail sections. not recommended. These rail sections are illustrated in Figures 52.1, 5.2 2, and 52.3 of this handbook. Trackside appliances such as electrical connection boxes, clean out drainage boxes, Rail Section Head Width drainage grates and special trackwork NP4a 56 mm (2.205 in) housings must be depressed or recessed in the vicinity of the rail head to provide for Ri 52N 56 mm (2.205 in) various wheel tread rail wear and rail grinding Ri 53N 56 mm (2.205 in) conditions. As a guideline, depressed notch Ri 59N Girder 56 mm (2.205 in) designs in the covers, sides and mounting bolts of the track enclosures adjacent to the Ri 60N Girder 56 mm (2.205 in) rail head are recommended. A depth of 15 GGR-118 Girder * 56 mm (2.205 in) millimeters (0.6 inches) provides adequate 128RE-7A Girder * 76.2 mm (3 in) clearance throughout the life of the rail installation. 149RE-7A Girder l 76.2 mm (3 in) 115 RE Tee Rail 69.1 mm (2.720 in) * Rail sections that are not currently rolled. 4.6.3 Embedded Track Types

If wheel tread width exceeds rail head width Chapter 2 documents the types and on the selected embedded rail, interference magnitudes of loads transferred from the between the outer edge of the wheel and the vehicle wheel to the rail. The rail must embedding pavement is inevitable as the rail support the vehicle and the resulting loads by wears vertically. As a rule, wheel widths from absorbing some of the impact and shock and 127 to 133 millimeters (5 to 5.25 inches) will transferring some of the force back into the overhang the rail head. The ATEA sought to vehicle via the wheels. The initial impact avoid such problems by having no standard absorber on the vehicle is the elastomer in the wheel tread more than 75 millimeters (3 resilient wheel, followed by the primary inches) wide and no standard plain girder rail suspension chevron springs, then the section head less than 63 millimeters (2.5 secondary suspension system air bags. The inches) wide. initial impact absorber on the track is the rail, specifically the rail head, followed by the A railway wheel or transit wheel that fastening or supporting system at the rail base overhangs the rail head must be clear of the and then the remaining track structure. The surrounding embedment material as shown in track structure’s degree of resiliency dictates Figure 4.6.1. Raising the rail head will the amount of load distributed to the rail and facilitate future rail grinding and delay the track structure and the magnitude of force need for undercutting or grinding the returned to the wheels and vehicle. surrounding embedment material to provide clearance for the wheel tread. Embedded track top of rail tolerances must be realistic 4.6.3.1 Non-Resilient Embedded Track when considering concrete slab placement Rail supported on a hard base slab, embedded during track construction. A projection 6 to IO in a solid material such as concrete with no millimeters (0.25 to 0.375 inches) above the surrounding elastomeric materials, has a high surrounding surface is realistic. Rail modulus of elasticity and will support the

4-64 Track Structure Design weight of the vehicle and absorb a moderate lose some of its resiliency after roughly 5 amount of the wheel impact and shock. A years. This hardening results in surface majority of the impact loads will be transferred deterioration from wheel contact, but does not back into the vehicle via the wheels. Non- progress to the point where it is detrimental to resilient rail can be considered as surrounding structures or otherwise continuously supported beam with a minor considered faulty by the general public. Like amount of rail base surface transfer. all engineered structures, these installations age and slowly deteriorate to the point where Non-resilient track has had mixed success. replacement is required. Eventual spalling of the surrounding embedment and surface failure are common Bituminous asphaltic embedment materials problems. This is especially evident in severe provide a minor degree of resiliency, but tend climates where freeze/thaw cycles contribute to shrink and harden with age, leading to to track material deterioration. Concrete excessive interface gaps between the rail and embedment alone does not provide rail asphalt or roadway concrete. When resiliency. It creates a rigid track structure bituminous asphalt hardens, it tends to that produces excessive unit stresses below fracture and break down. The resulting water the rail, causing potential concrete intrusion will accelerate deterioration of the deterioration. Such designs are highly entire track structure. dependent on the competency of the concrete immediately adjacent to the rails. Field quality As a guideline, although concrete embedment control during concrete placement and and bituminous asphalt materials have been vibration are very important. Rigid track was used in track paving embedment, they are not usually successful under relatively lightweight recommended. An elastomeric rail boot or trams and streetcars, but has often failed other elastomeric components are available to prematurely under the higher wheel loadings provide resiliency at the rail surface and of the current generation of light rail transit potential rail deflection both vertically and vehicles. horizontally.

The size and mass of the base slab, typically a concrete slab 400 to 600 millimeters (16 to 4.6.3.2 Resilient Embedded Track 24 inches) thick, tends to dampen some Direct fixation transit track and conventional impacts generated by passing vehicles. This ballasted track are both resilient designs with results in reduced and usually minor transfers a proven record of success. This success is of vibration to surrounding structures. due, in no small measure, to their ability to deflect under load, with those deflections Several transit systems feature embedded rail being within acceptable operating limits for suspended in resilient polyurethane materials. track gauge and surface. These rail designs This rather simple form of embedment are able to distribute loads over a broad area, completely encapsulates the rail, holding it thereby avoiding-except for the rail-wheel resiliently in position to provide electrical contact-point loading of the track structure isolation and full bonding of the rail and trough which could cause track failure. Resilient to preclude water intrusion. These track has been successful in ballasted track installations have been successful with no and direct fixation track installations and has visible defects. Experience has shown that had improved results in embedded track polyurethane has a tendency to harden and installations Non-resilient embedded track

4-65 Light Rail Track Design Handbook designs typically fail in excessive loading batts, and resilient fasteners. The decision to situations, such as a very sharp curve, where use floating slab design is based on site- the rigid nature of the embedment materials specific critical requirements and is often the prevents the rail from distributing loads over a preferred method to dampen and control the broad enough area thereby overstressing transfer of low frequency groundborne noise portions of the structure. A key goal in and vibration in the embedded track. embedded track design is to duplicate the rail deflections and resiliency inherent in ballasted Floating slab design consists of two concrete and direct fixation track systems to provide an slabs, with the initial base slab constructed on economical long-term track structure. the subgrade and a second slab that includes the track structure, with resilient isolators Rail supported on a resilient base, with a positioned between the two slabs. The base moderate modulus of elasticity, embedded on slab is usually U-shaped, making the entire a solid track slab will support the weight of the structure somewhat similar to the “bathtub” vehicle and absorb and distribute a greater concept. amount of the wheel impact and shock. Some of the impact load will be transferred back into The resilient isolators between the base slab the vehicle via the wheels. Resilient rail and the track slab can take several forms. evenly distributes vehicle loads along the rail Most common, particularly in older to the surrounding track structure. The installations, are large diameter elastomer frequency ranges developed by each light rail “hockey pucks” or “donuts” that are sized, vehicle will determine the parameters of the spaced, and formed to provide the desired resilient track structure design and its spring rate and acoustic attenuation. Some components. newer installations have substituted ballast mat sheets and rockwool batts for the donuts. The guidance of a noise and vibration expert In all cases, the secondary isolators must be is recommended to coordinate the design of placed between the sides of the track slab and the resilient track structure with light fail the vertical walls of the base slab to limit vehicles equipped with resilient wheels. Such lateral track movement and to provide wheels attenuate vibration caused by wheel- acoustic isolation. Those isolators can either rail contact, reducing the vibrations entering be individual elastomer blocks, continuous the carbody and affecting the ride quality. elastomer sheeting, or ballast mats extending They do not provide significant attenuation of up the base slab wall. As with any bathtub groundborne acoustic effects. design, the exposed joint between the track slab and the base slab must be well-sealed to limit water intrusion and accumulation of 4.6.3.3 Super Resilient Embedded Track surface contaminants in the voids around the (Floating Slab) base isolators, which will degrade the Groundborne noise and vibration are a system’s performance. Drainage of the void concern for embedded track sections adjacent area beneath the base slab is critical. The to or near noise and vibration sensitive design should provide for periodic inspection facilities, such as hospitals, auditoriums, and flushing out of the void area recording studios, and symphony halls. Numerous methods for controlling Based on site-specific rail features, vibration groundborne noise and vibration exist, radiation, and the distance to surrounding including floating slabs, ballast mats, rockwool structures, the floating slab, ballast mat or

4-66 Track Structure Desian rockwool batt design is best undertaken by a Other German companies in the elastomer noise and vibration expert experienced in component and product line have similarly dampening and isolation. For additional been experimenting with encased rail designs. information on noise and vibration, refer to Section 4 6.6 and Chapter 9. 4.6.4 Embedded Track Structure Types

4.6.3.4 A Special Resilient Rail Installation There are generally two types of track for Vibration Sensitive Zones structures in embedded track design: A relatively new track design concept to l Concrete slab track structure dampen vibrations is emerging in Germany. 0 Conventional ballasted track with The continuous elastic embedded rail system embedment as shown in Figure 4.6.2 consists of prefabricated sections of rail, rubber and steel 4.6.4.1 Concrete Slab Track Structure forms, preassembled for track installation. Concrete slab embedded track designs The assembled rail is supported under the consist of various styles that include: head with no rail base contact, providing l Continuous single-pour concrete slab with increased vertical deflection with controlled two rail pockets or troughs for the lateral deflection based on the elastomer installation of the rails (Figure 4.6.3). tapered configuration. The bolt tension and Stray current protection is provided at the compression of the rubber control total rail or within the trough area. deflection. The entire assembly is mounted on a concrete base slab with an intermediate l Two-pour concrete slab with cold joint grout material at the base of the assembly and between the two pours located at the base then embedded. of rail (Figure 4.6.4). Stray current protection is provided at the rail or within The reduction in vibration emissions in the the trough area. critical low-frequency range makes the l Three-pour concrete slab with continuous elastic rail system a viable a bathtub design providing stray current protection alternative to floating slab designs in below and beside the concrete track slab environmentally sensitive track zones. (Figure 4.6.5).

The initial concrete slab width can be designed to accommodate both single-track and double-track installations. As a guideline, the preferred design for ease of installation is two single-track concrete slab pours with an expansion or construction joint at the centerline of both tracks. The required accuracy of the track alignment and the finished top of rail concrete surface should Figure 4.62 Special Resilient Rail Installation for Vibration Sensitive Zones

4-67 Light Rail Track Design Handbook

STRAY CURRENT PROTECTION I- WITHIN THE TROUGH AREA

1ST POUR CONCRETE SLAB WITH TWO lNDlVlDLJAL RAIL TROUGHS FOR SINGLE TRACK. DOUBLE TRACK SECTIONS ARE ALSO POSSIBLE.

Figure 4.6.3 Concrete Slab with Two individual Rail Troughs

STRAY CURRENT PROTECTION IN THE RAIL AREA FOLD JOINT I jJ/ 2ND POUR CONCRETE I i SURFACE SECTIONS I jtl

t ST POUR CONCRETE SLAB FOR SINGLE OR DOUBLE TRACK SECTIONS

Figure 4.6.4 Two-Pour Concrete Slab with Two individual Rail Troughs

STRAY CURRENT PROTECTlON AT THE “BATHTUB” PERIMETER AREA

1ST POUR CONCRETE TRACK SLAB WITH “BATHTUB” DEPRESSION

Figure 4.6.5 Three-Pour Concrete “Bathtub” Installation

control the staging and methods of embedded rail in position without any mechanical track construction. connections between the rail and the track slab. The installation design is a two-step process. First, the rail is either positioned 4.6.4.1.1 Rail Installation within the trough (Figure 4.6.6A) or on the The methods of installation, positioning and initial concrete base slab (Figure 4.6.6B) retention of the rail depends on the specific using temporary jigs. Next sufficient trough or design criteria selected. base embedment material (concrete or polyurethane) is placed to completely Floating rail installation relies on the encapsulate the base of rail, thereby locking embedment materials to secure and retain the the rail in its final position. The temporary jigs

4-68 Track Structure Design are then removed and a second application of alignment during the embedment pours can trough fill material generally encapsulates the be especially difficult in curved track. The remaining rail to top of rail. contract specifications should require the contractor to submit a detailed quality control If girder rail is used, no special surface plan for meeting the tolerances. finishing is required. If tee rail is employed, either ,a flangeway can be formed on the Rail fastening installations use mechanical rail gauge side of the rail or the embedment base connections to secure the rail in position. material can be deliberately left low. The installation may consist of the following Regardless of rail section, the surface of the methods:

embedment material must be left low on the l Core drilling and epoxy grouting the field side of the rail to provide for false flange fastening anchor inserts or bolts to the relief and future rail wear. initial concrete dab as shown in Figure 4.6.7A. Meeting construction tolerances for floating l Cast-in-place fastening anchor inserts into rail installations depends on the contractor’s the initial concrete slab as shown in ability to rigidly hold the rails in proper Figure 4.6.7B. alignment during the initial embedment material pour. Once set, the rail position Such designs require limited horizontal and cannot be adjusted to meet construction vertical alignment adjustment prior to tolerances or future maintenance needs. embedment. This is provided by the leveling Irregularities in the rail alignment due to either nuts and slotted holes in the rail base plate as rail manufacturing tolerances or thermal shown in Figure 4.6.7A . Slotted plate holes effects during construction can cause may provide for horizontal adjustment and misalignments that can only be fixed by additional shims for vertical adjustment as removal and replacement. Maintaining the shown in Figure 4.6.7B.

SECOND FILL I.APPLICATION r...re SECOND FILL f -?NCRETE APPLICATION ;ECTlONS

Figure 4.6.6 Initial Rail Installations-Base Material

4-69 Light Rail Track Design Handbook

The use of steel ties or gauge rods is a factor

ANCHOR BOLTS in stray current control design. Individual DRILLED AND PLATE WlTH ANCHOR GROUTED 1N PLACE7 BOLTS CAST IN PLACE7 trough isolation is impossible due to the steel tie or rod extending beyond the trough or rail area. Gauge rods can usually be insulated within individual cross troughs; however the installation is cumbersome and quality control

CONCRETE SLAB is difficult. Steel ties are even more difficult A B due to their irregular cross section. Figure 4.6.7 Rail Fastening installations The use of steel ties and gauge bars in Rail fastening embedded track designs must embedded track sections tends to produce a consider the ability of the rail to distribute surface crack in rigid pavements directly lateral loads to the rail fasteners. If the rails above or near the embedded tie or bar. To are rigidly secured at centers of 900 to 1000 control surface deterioration, a scored crack millimeters (approximately 35 to 40 inches), control slot or indentation is recommended. and the surrounding embedment materials are This may not be specifically necessary in more flexible, the track will have hard spots installations where the pavement surface that will cause the rail to wear abnormally. consists of brick or other individual pavers. Elastomer pads should be considered to dampen the hard spots. Direct fixation rail 4.6.4.1.2 Stray Current Protection fasteners may be used to secure the rail to the Requirements base slab. The fasteners provide resiliency in An effective mitigation barrier against stray all directions as well as electrical isolation. current corrosion is to protect both the rails and nearby metallic structures from Anchor plates may also be used. The benefits electrolytic corrosion. The track structure of using anchor plates in embedded track are: requires an electrical barrier be provided at l Rigid control of rail position during two- the rail location as shown in Figure 4.6.8, pour initial installations unless the bathtub design (Figure 4.6.5) can l Anchor plates can be reused during future confine currents within the overall track rail changeout to control rail position structure. Refer to Chapter 8 for additional details on the theories of stray current. l Track can be used in partially completed installations to either confirm track Principal measures to minimize traction installation or maintain revenue service current leakage are: Steel ties or gauge rods can be intermixed l The use of continuous welded rail with anchor plates in embedded track to assist providing superior traction power return in controlling the rail and establishing the track over conventional electrically bonded gauge. Gauge bars spaced at 1,500 jointed track. millimeters (5 feet) on curves and 3,000 l Insulating either individual rails or the millimeters (10 feet) on tangents are common. entire track structure from the earth. Steel ties in every fourth fastening position may also be considered.

4-70 Track Structure Design

BARRIER SPANS BOTH SURFACES l Ductwork that must be provided in the TO PROMDE LARGER EQUAL BONDING SURFACES FOR RETENSION I embedment materials. 0 Provision for rail bond jumpers exothermically welded to the rail on either side of a bolted joint or completely around special trackwork components prior to embedding the track.

Prior to installation of the embedded track structure, a corrosion survey should be bNSULATlNG BARRIER undertaken to establish the existing baseline Figure 4.6.8 Insulating Surface Barrier at stray current levels. Periodic monitoring Trough Edges should be performed after installation of embedded track to detect current leakage and Insulating embedded switch machines to control or improve insulation performance. and any other track system appliances from the earth. Stray current protection design can include one or more of the following concepts: Continuous welding of the steel Coating of the rail surface (except the reinforcement in the supporting base slab head and gauge face) with an insulating to act as a stray current collector and dielectric epoxy such as coal tar. electrical drains to carry intercepted current back to the traction power Embedding the rail and filling the entire substation. trough with an insulating dielectric polyurethane or other suitable insulating Cross bonding of rails with cables material. installed between the rails to maintain equal potentials for all embedded rails. Lining the rail trough with an insulating dielectric material, which provides a Rail bond jumpers at mechanical rail barrier between the potentially conductive connections, especially within the special trough fill material and the concrete track trackwork installations. slab.

Key details concerning the above measures Lining the rail in an elastomeric boot, that affect the track structure design are: thereby totally encapsulating the surface Type of insulation to be installed, whether except for head and gauge face. it is located at the rail face, along trough Insulating the anchor bolts or anchor edges, or around the entire periphery of inserts that require insulation due to the track structure as in the bathtub penetration beyond the insulated rail concept. trough zone into the base concrete track Type of insulation to be installed at switch slab. This insulating design can be mechanisms or track mechanisms accomplished by either coating the Provisions for cross bond cables between penetrating stud or anchor insert to rails on each track and occasionally provide a continuous seal at the base of between rails on different tracks. the concrete trough or insulating liner location.

4-71 Light Rail Track Design Handbook

l insulation at the trough edge containing the rail base not in contact with extruded the rail is critical in stray current corrosion sections, is an important requirement. control, including the interface at the top Extruded sections are available in separate of embedment. A wide band or insulating parts that encase the entire rail as shown in barrier is required to retard surface Figure 4.6.9 These designs require a current leakage through water, dirt and specific concrete base installation sequence debris that may accumulate on the to provide complete support under the base of surface as shown in Figure 4 6.8. rail. As an insulating material, extruded elastomer has proven to meet the required Additional information on corrosion control is bulk resistivity of IO” ohm-cm that is needed included in Chapter 8 of this handbook. to be effective.

4.6.4.1.3 Rail Embedment Materials Rail embedment or trough fill materials range from very elaborate and expensive to simple and moderately priced, including elaborate extruded elastomer sections, cast-in-place resilient polyurethane components, concrete fills of various compositions, and an asphaltic bituminous mortar FIRST POUR

Embedment designs for resilient track that Figure 4.6.9 Extruded Elastomer Trough utilize the general track structure, as Components described above, have incorporated the 4.6.4.1.3.2 Resilient Polyurethane. following materials to retain and allow for Polyurethane components can be used as designated rail deflections with varying trough fillers. Resilient polyurethane has success. proven to be an ideal rail base support 4.6.4.1.3.1 Extruded Elastomeric Trough material that provides a minimum of rail Components. Extruded elastomeric sections deflection. Altering the urethane compound to or components are designed to fit the rail adjust its durometer hardness can control the contour. Generally these materials are only actual amount of deflection. placed above the base of rail and other Elastomeric polyurethane is an effective stray measures must be taken to prevent stray current protection barrier that binds well to current migration from the rail base. Using both cleaned rail surfaces and concrete trough extruded insulation requires the two-pour surfaces. It is, however, expensive, both for method for base slab installation, including material procurement and the labor installation of the rail prior to placing the associated with mixing and installation. To surrounding extruded component sections. reduce the volume of polyurethane required, Finally the top pavement is then placed on the premolded rail filler blocks shaped to fit the gauge and field sides of the extrusion. Stray web of the rails can be used as shown in current corrosion protection may be provided Figure 4.6.10. The embedment design must by the material used to fabricate the extruded consider rail base deflections. Embedment sections. Providing insulating protection to materials for the rail head and web areas the total rail surface, including any portion of

4-72 Track Structure Design

MB FtLLER BLOCKS TO damage the elastomer pads, proper drainage ZND POUR TROUGH FILLER REDUCE TROUGH FILL TO THE TOP Gf RAIL WlTH MATERIAL OUANTITY of the rail trough should improve performance, FORMED FLANGEWAY 7 provide assurance that the expected life cycle will be realized, and increase the effectiveness of the pads as a stray current deterrent The embedded track design must consider rail base deflections with matching resilient rail web and head embedment L IST POUR TRDUGti FILLER ABOM THE BASE RAIL materials to atlow for rail movement. Solid or Figure 4.6. IO Polyurethane Trough Filler non-resilient embedment materials with Web Blocks surrounding the rail will defeat the elastomer pad’s resiliency and lead to premature failure should both be resilient in nature to allow for of the non-resilient materials. the rail movement. Solid or non-resilient encasement materials surrounding the rail will As an insulating agent, either synthetic negate the resilient characteristics of the elastomer compounds or natural rubber have polyurethane and lead to premature failure of met required bulk resistivity of 10” ohm-cm. the non-resilient materials. 4.6.4.1.3.4 Elastomeric Fastenings (Direct Polyurethanes are a difficult and expensive Fixation Fasteners). To duplicate successful material for in-track construction. Urethanes open direct fixation track design with are highly susceptible to chemical reaction acceptable rail deflections, embedded track with moisture in the air, the fine sand additive designs have incorporated direct fixation for bulk, and surface dampness during concepts. Bonded direct fixation fasteners application. Their chemical characteristics and component plate and elastomer pad make it essential that mixing, handling and fastenings may be considered application be undertaken carefully by qualified contractors. Polyurethanes in the Successful direct fixation fasteners or liquid form seek a level surface, adding to the fastening designs are essential to embedded difficulty of installation in embedded tracks track design. Direct fixation fastener design with an inclined profile grade line. features are discussed in Chapter 5 of this Handbook. As an insulating material, polyurethane has proven to meet the required bulk resistivity of The embedment design must consider rail 10” ohm-cm. deflection at the fastener. The surrounding embedment materials must be resilient, with 4.6.4.7.3.3 Elastomer Pads for Rail Base. extruded prefabricated sections that conform Elastomer pads are a satisfactory rail base to the rail fishing zone with clearance support material that provide a minimum apertures for the fastener and clip assembly amount of rail deflection depending on the as shown in Figure 4.6.11. Solid or non- spring rate of the elastomer and its specific resilient embedment materials surrounding the durometer hardness. Natural rubber rail will defeat the direct fixation fastener’s elastomer pads mixed with proper quantities resiliency and potentially lead to premature of carbon black and wax have exhibited failure of the non-resilient materials. satisfactory performance and long life. Although water seepage typically will not

4-73 Light Rail Track Design Handbook

tee rail sections and popular girder groove APPETURE FOR SPRING CLIP and guard rail sections. Boots are also DIRECT FIXATION EMBEDMENT FASTENER --\ available for dual tee rail and bolted restraining rail assemblies.

As an insulating material, the rail boots have met the required bulk resistivity of 1012 ohm- cm.

4.6.4.1.3.6 Concrete and Bituminous Asphalt Trough Fillers. Concrete, RUNOFF PIPE cementitious grout components are available Figure 4.6.11 Direct Fixation Fastener with to use as trough fillers. The first-pour trough In ternal Drain System filler encapsulating the rail base and providing continuous support below the rail can be a Direct fixation fasteners with surrounding non-shrink cementitious grout. The flexible elastomers are subject to infiltration cementitious grout with a reduced aggregate seepage into the rail seat cavity. Although size, less than 12 millimeters (0.5 inches) to water seepage may not seriously damage the ensure the rail base cavity is entirely filled, elastomer components, proper drainage should be placed from one side of the rail to should improve performance and provide be certain no voids are formed in the base electrical insulation at the direct fixation cementitious pour. fastener for stray current control. The second-pour trough filler, which As an insulating agent, direct fixation completes the cavity fill, can be a concrete fasteners meet the required bulk resistivity of mix with a 20-millimeter (0.75inch) aggregate 10j2 ohm-cm. size. Application of silicate fume ash to the concrete mix has proven beneficial in 4.6.4.1.3.5 Rail Boot for Embedded Track. controlling stray currents. To control eventual Rail boot designs have proven to be a concrete shrinkage cracks, polyethylene fibers satisfactory rail base support material that 50 to 65 millimeters (2 to 2.5 inches) long can provides minimal rail deflection depending on be included in the second-pour surface trough the design. Natural rubber elastomers mixed filler. with proper quantities of carbon black and wax exhibit satisfactory performance. Both filler materials should have a minimum Configuration of the elastomeric rail boot with concrete strength of 27.6 MPa (4,000 psi) at voids and the elastomer spring rate allow for a 28 days. specific magnitude of rail deflection both vertically and horizontally. Bituminous asphaltic components have been used as a trough filler material. Similar care The rail boot installation design is subjected to must be taken during placement to be certain water seepage entering both inside and that voids are not generated at the rail outside the boot area. To improve support. Bituminous asphalt materials with performance, proper drainage of both areas of resistivity characteristics can be used as an the rail installation should be provided. Rail insulating barrier. boot designs are currently available for both

4-74 Track Structure Design

4.6.4.1.4 Embedded Track Drainage pavement is crowned in the conventional in all but the driest climates, the success of manner, the pavement cross slope results in any embedded track design will depend the track being out of cross level in tangents directly on the efficiency of the embedded and perhaps even negatively superelevated tracks drainage systems. This includes not curves For additional information on only systems for intercepting surface runoff, surfacing and cross level refer to Chapter 3. but also methods for draining water that seeps into the rail cavity zone. Experience has Whenever possible, the profile and cross shown that surface water will seep and section of the road should be modified to accumulate in the rail area, particularly around conform to the optimum track profile and cross the rail base and web. This moisture can section. This often requires that the roadway cause rail corrosion and deterioration of the geometry be compromised to accommodate surrounding embedment material, eventually rail elevations, curb and gutter elevations, and leading to failure of the pavement and the rail sidewalk grades. fastening system. The surface runoff entering the flangeways Drainage of the rail embedment trough or should be minimized and trackway road cavity is of the utmost importance. Sealing surfaces should slope away from the rail the interface between the rail and the locations. Some transit system designs have adjoining embedment material is virtually sloped the road surface within the track gauge impossible. Similarly, construction joints area toward the track centerline and the between the rail trough and slab concrete or “dummy gauge” zone to a line of drains surface sealants are susceptible to potential midway between the tracks. The road water seepage. Regardless of how well the surfaces on the field side of the rails should surface sealants are designed and installed, slope toward the curb line or the surrounding seepage will eventually occur and possibly roadway surfaces. lead to deterioration or disintegration of the fill components, particularly in climates Inevitably, some runoff will get into the susceptible to freeze/thaw cycles. To prevent flangeways. This water must be drained this, the embedment trough or rail cavity zone away. Transverse lateral drainage chases must be designed with a reliable permanent should always be provided at low points on drainage system as shown in Figure 4.6.11. vertical curves, immediately up-grade at embedded special trackwork and at transitions Another penalty of poor drainage or no between embedded track and any open track drainage is that trapped or standing water can design. Additional drainage chases should be result in unacceptable levels of stray current provided periodically along straight track leakage, particularly in areas where streets grade sections so that runoff, debris, sand, or are salted. other material can be carried away and the flangeway kept relatively clear. 4.6.4.1.4.1 Surface Drainage. Embedded track installations complicate pavement Drains in embedded track areas are typically surface drainage because the exposed rail transverse drains or drainage chases head and flangeways intercept and redirect perpendicular to the rails. They consist of a stormwater runoff. The road profile and cross grate-covered chamber that is connected to slopes direct the runoff toward the rail and the adjacent storm sewer system. The design flangeways. In addition, if the roadway of the rail through the drainage chase opening

4-75 Light Rail Track Design Handbook should consist of the exposed bare rail transverse drain can act as a dividing point supported on each side of the chase, wherein between the different designs used in the rail acts as a suspended beam. The embedded main line track and special bottom of the track flangeway must have an trackwork. opening wide enough to ensure that it will not become clogged with leaves or other debris. 4.6.4.1.4.2 Internal Drainage. Embedded This is easily undertaken with tee rail track systems require internal drainage of the construction. If girder rail is employed, it is rail cavity zone when loose extruded common to machine a slot in the bottom of the components or non-adhering trough fill flangeway. Such slots typically cannot be materials are selected Polyurethane fill much more than 25 to 30 millimeters (1 to material totally encapsulating the rail and 1.125 inches) wide. They also frequently get bonded to the trough walls does not appear to clogged. Where clogging is likely, an require internal drainage. Drainage slots improved design might be to cut away the perpendicular to the rail base should be girder rail lip in the drainage chase area. provided for adequate drainage at the base of the rail or the bottom of the rail trough zone. When the embedded track design includes Longitudinal drain pipes outside of the rail individual longitudinal troughs in the concrete trough and fastening system should be for each rail, the transverse track drainage provided to collect and carry accumulated chases can also drain seepage from the inner water away from the rail cavity zone as shown rail trough or rail cavity. The design exposes in Figure 4.6.12. the end faces of the concrete rail troughs on each side of the drainage chase as shown in Figure 4.6.12. The exposed faces can be 4.6.4.2 Ballasted Track Structure With utilized as rail trough or rail cavity drainage Embedment systems. Frequent drainage chases, spaced Early 20th century embedded track designs less than 150 meters (500 feet) apart, should for urban trams included ballasted track with be considered and connected to the internal timber crossties constructed to railway longitudinal drainage pipe system to provide standards and subsequently embedded to the adequate drainage and allow periodic top of rail. These standards still exist today maintenance flushing of the system. and are perpetuated by the original transit agencies, although contemporary embedded The transverse trough drains should act as track designs are being contemplated. lateral drainage collectors for the embedded longitudinal drain pipes. The longitudinal Embedded track design using standard drain pipes, opened at the trough drains, can ballasted track design requires use of a fill also be used for periodic flushing of the material to the top of rail as shown in Figure embedded pipes. This provides a continuous 4.6.43. In contemporary track design, the and maintainable drainage system. negative return running rail must be insulated Transverse trough drains should be placed to control or confine stray current leakage. immediately in front of switchpoint Typical ballasted track elements used in components to protect embedded special embedded track design include an insulating trackwork installations. Transverse drains in barrier at the rail, tie plate and fastening to these locations collect water that drains isolate the rail from the timber or concrete toward the special trackwork In addition, the

4-76 rCHANNEL GRATES BOLTED IN POSITION HIGH DENSITY POLYETHELENE PROVDES STRAY CURRENT PROTECTION r RAIL TROUGH

BOOT ENDS EXPOSED AT DRAINAGE CHASE TO NOTE: ALLOW LONGITUDINAL SEEPAGE DRAIN DRAINAGE CHASE AT SPECIAL TRACKWORK BOUNDARIES TO BE MODIFIED TO DRAIN LONGITUDINAL DRAIN PIPE FOR BATHTUB AREAS AND SPECIAL TRACKWORK DRAINING & FLUSH CLEANING COMPONENTOPENINGS

Figure 4.6.12 Cut Away Section Embedded Track Drainage Chase

POLYETHELENE DMDING SHEET NOTCHED AT FASTENING -A INSULATING COVER EMBEDMENT CONCRETE AT FASTENING p\ (OR OTHER MATERIAL) lNSULATlNG COVER FLANGEWAY- \

q -. . . -. . 0’ Q a 0 * . w BALLAST BED F. . . . - BALLAST BED

RAILsEcn0ti AT TIE RAILSECnON AT THE CRIB Figure 4.6.13 Ballasted Track Structure with Embedment

4-77 Light Rail Track Design Handbook crosstie and the surrounding embedment treatment and quite possibly a different design concrete or other fill material. concept from the main line embedded track design. The embedded ballasted track structure is a proven standard that provides a long, durable In contemporary light rail transit systems, track life with minimal maintenance, other than embedded special trackwork generally rail grinding and occasional road surface consists of turnouts grouped to act as single repair for more serious deterioration. This crossovers for alternate track operations. longevity can be attributed to the built-in Operating requirements may dictate the drainage system provided by the ballast and installation of a double crossover with four sub-ballast trackbeds. However, this drainage turnouts and a crossing (diamond). An system also experiences ballast abrasion and extensive embedded track transit system settlement that degrades track performance. could utilize complex embedded special Embedded ballasted tie track has a history of trackwork arrangements beyond simple single inferior rail and road surface alignment. This and double crossovers. For additional includes rails sinking below the top of the information on embedded special trackwork embedment or road surface, fracturing of the design, refer to Chapter 6. embedment surface especially at the designated crosstie spacings, concrete The magnitude of the components, the surface fractures, and bituminous concrete requirements for stray current protection, and surface cracks and sagging between the need to secure the components dictate crossties. special trackwork embedment design. Stray current protection at the rail face, as well as Embedded ballasted tie track installed with an component surfaces with irregular independent roadway surface such as brick, configurations, potential gauge bars and pavers or Belgian Block with a sand mortar gauge plates, may be difficult. To simplify the were relatively successful. The success of installation, the bathtub design concept is the old systems, it is believed, was due recommended for embedded special entirely to the flexibility of the brick and trackwork. blockstone pavements and their resultant ability to adjust to vehicle loads and thermally The bathtub design allows for stray current induced movements. The key to this was the protection to be clear of the special trackwork use of hot tar to seal the joints between the switches, frogs and crossing (diamond) pavers, thereby excluding most moisture. The components. This simplifies trackwork down side was extensive electrolytic corrosion installation and improves stray current due to the base of rail being in contact with protection as shown in Figure 4.6.14. ballast and the sand bedding of the pavers. Their performance in this regard might be Embedded special trackwork will also require improved by an insulated bathtub design. the use of special plates to support the various track elements. These must be designed to develop uniform deflections. 4.6.5 Embedded Special Trackwork

The embedded special trackwork portion of any transit system will require special

4-78 Track Structure Design

STRAY CURRENT PROTECTION AT THE “BATHTUB” PERIMETER AREA IST POUR TROUGH FILLER TO THE BASE OF RAlL ND POUR TROUGH FILLER TO THE TO F RAIL w1Ti-l FORMED FLANGEWAY TYPICAL SPECIAL TRACKWORK COMPONENTS ANCHOR BOLTS DRILLED MOUNTED ON LARGE PLATE FASTENINGS

I

2ND POUR CONCRETE SPECIAL TRACKWORK BASE WITHIN BATHTUB CONCEPT

Figure 4.6.74 Special Trackwork-Embedded “Bathtub” Design

4.6.6 Noise and Vibration Noise and vibration control should be considered in the vehicle truck design, Vehicle wheel loads are transmitted from the particularly with respect to the use of resilient wheel/rail interface to the track structure. wheels and the details of the primary Unlike ballasted or direct fixation track with suspension system. The primary suspension load distribution to the ties or fasteners, is located between the journal and the truck embedded track uses a concrete slab and frame. The primary suspension continuous elastomeric system to distribute characteristics are dependent on the spring the load throughout the surface of the rail elements, number of layers or total deflection, base. This design concept spreads the load and their angular formation. The elastomeric more evenly along the resilient rail installation. spring of the suspension reduces noise by Embedded track with a fully supported rail acting as a vibration isolator. It also acts as a base provides an improved track structure. barrier to the transmission of structure borne noise. Resilient elastomers dampen the rail, reducing rail vibration and rail-radiated noise. The In selecting the suspension characteristics of resilient elastomer controls the degree of the extruded elastomer, elastomeric base pad, vibration and deflection. A softer elastomer or the rail boot elastomer used to support the provides a lower spring rate in the elastomer rail, vehicle parameters such as normal material, leading to reduced vibration in the weight and crush loads must be considered. rail . Each light rail vehicle, with different truck suspensions, wheel bases and weights, may The spring rate is used in determining the require a different track dynamic suspension track modulus or track stiffness and the system. The advice of a noise and vibration amount of vertical deflection in the rail. The expert in this endeavor is recommended as elastomer, in conjunction with the vehicle stated in Chapter 9 of this Handbook. suspension system, affects the vehicle/rail interface - specifically, track performance, noise, and vibration in the immediate rail area.

4-79 Light Rail Track Design Handbook

4.6.7 Transit Signal Work the contact wire remains near the track centerline. Transit signal requirements in embedded track sections differ from the general design The traction power return system definitely standards for ballasted and direct fixation impacts the design of the rail installation in track. Embedded track within city streets or embedded track. Unlike ballasted and direct transit malls may be exposed to mixed traffic fixation track standards, where the rail is conditions and may share the right-of-way actually insulated from the ground at the base with automobiles, trucks and buses. Signal of rail or within the fastening system, the equipment, such as switch machines or loops entire rail surface except top of rail and gauge for train-to-wayside signals, may need to be face must be insulated in embedded track installed in this area. Space must be provided designs This requirement contributes to the to mount these devices as well as drainage challenge of designing embedded rails that pipes and conduits for cables to control these provide an insulated, resilient and durable devices. Conduits for power and track circuits track system using off-the-shelf materials. may be needed. Reinforcing bars in the concrete may impact the reliable operations of Embedded ductwork within the track structure track circuits. provides access for power cables and cross bonds to achieve equalization in the rails.

4.6.8 Traction Power For additional information on stray current control and traction power, refer to Chapters 8 Traction power requirements in embedded and 11, respectively. track sections differ from the standards for ballasted or direct fixation track. The immediate traction power impacts of catenary 4.6.9 Typical Embedded Concrete Slab pole location and isolation of the negative Track Design Guideline return rail play a major part in embedded track design. Embedded track areas in downtown The previous sections describe the various business sections, on city streets and in embedded track concepts, designs, and transit malls generally avoid positioning materials available to the track designer. The catenary poles between the tracks. The issue track designer must develop a set of of catenary poles within central business installation drawings and corresponding districts is so controversial that, in many specifications to allow for construction of the designs, the contact wire and catenary system embedded track segments of the transit was suspended from the sides of existing system. These must reflect an understanding buildings or on poles in sidewalk areas. The of the various track and vehicle parameters. total system and track design must consider A typical embedded track design guideline catenary pole locations that blend into the follows. The design described herein is existing environment without severely arbitrary; actual track design should be impacting the current roadways, sidewalks developed by the track designer based on and general public’s perception of an area. site-specific requirements, economics, and The tight track curvature within central aesthetics to match the environment. The business districts also impacts the design and goals of embedded track design are to installation of the catenary system, because produce a track system that provides long- many more poles are needed to ensure that Track Structure Design

term performance, with a minimum of individual tie plates, as well as anchor interference to the neighboring structures, and bolts. This creates a cold joint at the base is relatively easy to maintain or replace. of rail. After the base slab is poured and cured, The embedded track design guideline is the track is available for vehicle testing illustrated in Figure 4.6.15. The author, as a and operation track designer, selected this embedment arrangement for the following reasons. The forming of two rail troughs provides a . This embedded track design allows for joint that facilitates concrete removal for shared street operation with other replacement of worn rail. vehicles or may be used in a pedestrian The use of a rail boot or other insulating mall. elastomeric system is needed to isolate . The vertical and horizontal position of the rail The rail boot is shown, but any of concrete base slab is established by these systems may be equally effective. survey, using the constructed skeleton The elastic spring clip arrangement track method. simplifies the rail hold down and provides l The concrete base slab first pour encases a degree of rail base flexure the steel ties or leveling beams and

(;, OF TRACK NOTE: 1 l-l-+ @J PLATE f THE ITEM NO’s REFER r TO DESCRIPTIONIN TRACK GAUGE a SECTION 4.6.9 EMBEDDED I-TRACK DESIGN GUIDELINE.

i SLOPE ’ SLOPE -

SUBGRADE AND i @ 0 SUB BALLAST

Figure 4.6.15 Typical Embedded Track Design

4-81 Light Rail Track Design Handbook

l The protective covers over the rail d The concrete base slab fastening components allow for their encases and secures the reuse at the time of rail replacement. The embedded track rail fastening intent is to retain the steel ties and system. individual plates in the base slab pour, e The base slab has concrete allowing for similar rail section positioning placed up to the base of rail or and rapid replacement. This facilitates a resilient boot. This provides a quick return to revenue service construction cold joint between operations. the first and second concrete pours, just below the trough fill The following notes are meant to augment the material embedding the rail. detailed embedded track design shown in The finished base slope in the Figure 4.6.15. The item numbers refer to the trough zone should be sloped component number in the figure. toward formed drainage slots. Item 1 This includes the well- Item 3 a. The embedded track drainage compacted subgrade and sub- system built within the concrete ballast system with an adequate base slab consists of transverse storm drainage system track drainage chases and a connected to existing or new longitudinal drainage system at street storm drains. A the rail cavity zone. protective barrier sheeting, b. The transverse track drainage Styrofoam barrier, or rockwool chases are placed at 150- to batts at the top of sub-ballast 200-meter (500- to 650-foot) system may be considered for intervals and strategically vibration and noise attenuation. positioned at vertical curve Item 2 a The reinforced concrete base sags, special trackwork slab (first pour) should have a approaches, and the ends of minimum thickness of 300 to embedded track locations. 350 millimeters (12 to 14 These control surface runoff and inches), to act as a vibration internal rail cavity drainage. absorption barrier and provide C. The transverse track drainage support to the track structure. chases act as lateral runoffs for b The base slab may be a single- the embedded longitudinal rail or double-track configuration as cavity drain pipe system. needed for specific street d. The concrete base slab contains configurations. Concrete pours a longitudinal drain pipe and may be single or double track, periodic drain slots parallel and depending on track centers. adjacent to the rail to drain the c The concrete base slab contains rail zone. an internal longitudinal track e The longitudinal drain pipe drainage runoff system with should be positioned clear of the provisions for deeper transverse rail fastening system. track drainage chases.

4-82 Track Structure Des&n

f. Drainage systems that are installed providing a void in the invisible once the construction is trough embedment material. completed will almost never d The insulating rubber boot must receive the maintenance be a continuously bonded attention required The ease of system, utilizing connector maintenance is critical to a splices overlapping the boot successful system. configuration. To promote Item 4 a. The rail fastening system internal boot drainage of the consists of steel ties and zone between the rubber boot individual steel plates with and rail surface, special drain appropriate spring clips, welded hoses are incorporated. The shoulders, protective insulators drain hoses are positioned in for rubber boot, and a protective the existing drain slots adjacent housing for the spring clip area. to the rail trough. They project into the center of the PVC b. The steel tie is embedded in the longitudinal drain pipe, to initial concrete base slab with provide the required stray the top of tie level with the top of current protection. concrete pour. The steel plates should similarly be embedded to e. The resilient elastomer rail boot the top of concrete. The steel must be continuous, providing a plates are secured to the initial void or holiday free insulation concrete base slab by anchor system to retard stray electrical bolts or studs. current leakage.

C. The concrete finish in the rail Item 6 a The surface slab (second pour) base area between the steel tie is approximately 180 millimeters and plates is trowelled smooth. (7 inches) high and is placed to the top of rail Block outs for rail Item 5 a. The rail is encased in a resilient troughs are formed. The elastomer boot or liner, surface finish is determined by positioned on the steel tie rail specific transit requirements, seat area and the individual architectural treatment and the mounting plates. The rubber type of roadway traffic or booted rail is fastened to the ties pedestrian mall. and plates by spring clips. The clips have rubber protective rail b. The top surface is finished with base insulators at each slopes away from the rail cavity shoulder. toward the centerline of track and the field side of rail. These b. Rail deflection is provided sloped portions within the track through the resilient rubber boot gauge drain longitudinally along liner and minor deflections of the track to the transverse the spring clips. drainage chases. C To allow for rail deflection and C. The placement of the surface movement at the spring clips, a slab completes the longitudinal special protective cover is

4-83 Light Rail Track Design Handbook

drainage slots from the rail the rail and fastenings cavity to the longitudinal drain completing the surface roadway. pipe. b. The surface finish includes a d. The top concrete surface slab gauge side flangeway for tee rail requires embedded PVC or entire capsulation to the top casings for traction power or of the girder rail lip. The field signal connections between the side has a depression of 6- rails or tracks. Provision should millimeter depression (0.2- inch) be made for rail connection throughout, with special boxes, drainage boxes and depressions in the fixed periodic transverse drainage adjacent trackwork accessories. chases. This allows for rail grinding.

Item 7 a. The running rail is insulated for C. The surface slopes beyond the stray current control utilizing the flangeway and wheel tread rail boot concept The running depressions slope away from rails can be either tee rail or the rail head. Track gauge girder groove rail. pavement slopes intersect at the center of track. Field side b. The running rail is continuously pavement slopes away from the welded rail (thermite welded or rail area towards the curb lines. flash butt) wherever practical. Precurving of the rail may be These design concepts are representative of required to facilitate restricted the type of considerations required to design street alignments that result in embedded track. An alternate set of sharp track curvature. The weld parameters will require a similar design finish is flush with the parent rail process to coordinate and interface the steel surface to allow for proper various disciplines involved. The key design boot fit. features of any track installation include c. Various trackwork accessories adequate drainage, corrosion control, adjacent to the rail must be insulating protection, noise and vibration individually designed to suit the abatement measures, and accommodation for rail boot insulation in order to signal and traction power components. minimize electrical stray current. Understandably, the track design and vehicle design must be compatible for the d. The booted rail is checked for development of a successful transit system. insulation, clip application, and the track position is confirmed prior to application of the 4.6.10 Turf Track: Another Type of protective housing and the Embedded Track installation of trough fill. Item 8 a. The rail trough embedment Over the years, European light rail transit concrete fill (third pour) is systems have found a need to blend the placed only after confirmation transit track and system into the landscape. that rail installation is correct. To fulfill this requirement, a specific track The embedment encapsulates design similar to embedded track or partially

4-84 Track Structure Design embedded track has evolved, recognized as main standards. Landscape embedded track “turf track II The turf track standard consists of was developed for selected purposes: concrete plinths or beams running parallel l Reduce the visual effect of ballasted track under the rail to support the track The rail is l Reduce the noise from trams to the installed on elastomer base pads. The rails utmost extent are connected to retain gauge with l Provide year-round greenery in the vicinity conventional gauge rod bolted to the web of of the track the rail. The base of rail is not connected to the concrete plinth. The rail web area is filled A select turf is required to grow to a maximum with a prefabricated filler block that adheres to height of 30 to 40 millimeters (1.2 to 1 6 the rail. The top of the rail and the filler block inches) requiring minimal watering and is sealed with a bituminous sealant. The maintenance Landscape track has proven to vegetation is a special blend of plants reduce noise by 6 to 8 dBA. Other types of expected to retain a stunted growth and landscape track structure can be designed to require minimal cutting. The filler blocks and suit the needs of specific locations. To ease the bituminous sealant provide the stray the concerns of communities and residents current protection. Figure 4.6.16 shows a along certain sections of the light rail system typical turf track installation. about transit-related impacts, turf track or some specific track design may prove to be Many European cities appear to be adopting very beneficial. turf track or track landscaping as one of their

CONCRETE EDGING AND TURF SURFACE LEVEL WITH ($ TRACK ORGANIC TOP OF RAIL I -SECOND POUR F’LL gL TuRF 1 r 1435 TRACK GAUGE I /,-DOWEL PINS SAND w i 4 I\ :

STEEL LEVELLING BEAM I IeF

-FIRST PC LFIRST POUR. . ~I-MJ-vv., .INUOUS \COMPACiED -. .- ROAD BED CONTINUUUS CONCRETE PLINTH SLAB CONCRETE PLINTH SLAB _ SIDE WITH PLINW _f _ SIDE WTH TRACK 1 TIE CONNECTION

Figure 4.6.16 Turf Track-Another Type of Embedded Track

4-85 Lioht Rail Track Desion Handbook

4.7 REFERENCES [4] AREA Manual of Railway Engineering (1984) Chapter 22. [I] Albert S. Rickey, Electric Railway Handbook, Second Edition, McGraw-Hill [5] A.N. Talbot, “Stresses in Railroad Book Company, Inc., 1924. Track”, Reports of the Special Committee on Stresses in Railroad [2] William W. Hay, Railroad Engineering Track, Proceedings of the AREA, First Second Edition, A Wiley - Interscience Progress Report, Vol. 19, 1918, pp. Publication ISBN O-471-36400-2. 873-l 062, ibid., Second Progress Report, Vol. 21, 1920, pp. 645814. [3] Wilson, lhrig & Associates, Inc., “Theoretical Analysis of Embedded Track Vibration Radiation, San Francisco Municipal Railway,” Technical Memorandum to Iron Horse Engineering co.. 7/l 7197.

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