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26 consider it to be within acceptable limits. Santa Clara VTA without jerks, pitching, or yawing. The wheel tread profile is noted issues with wheel squeal on both high-floor and low- critical. If uneven wear occurs, the variation in wheel profile floor cars but consider that, in both cases, the noise does not will cause a poor ride, so variations in wheel profile need to exceed limits. be kept within tolerance limits. The track quality needs to be In general, systems may have issues, perhaps only at certain high in terms of gauge and other variations. locations, but they have been able to manage them effectively. 3.6 Contributing Factors 3.4.3 Solutions 3.6.1 Vehicle Parameters In general, noise can be reduced on tangent track by main- Truck Wheelbase taining rail smoothness. The use of resilient wheels and other forms of damping may reduce squeal on curves but not nec- The main effect of varying the center truck wheelbase essarily eliminate it. Squeal may be controlled by use of lubri- would be to increase the critical angle of attack on very sharp cants or possibly using different metals for the wheels and curves. The angle of attack would typically be 2.5 degrees on rails, although the latter theory has not been fully tested. a 25-m (82-ft) curve for a 1.9-m (6 ft 23/4 in.) truck and would The use of special trackwork designed to reduce the risk of change by about 0.1 degree for each 50-mm (2-in.) longer or derailment with LFLRVs will probably have the added bene- shorter wheelbase dimension. Therefore, the effect is very fit of reducing noise associated with this type of track, assum- slight. In practice, there is very little variation among vehicle ing that discontinuities are eliminated. designs. Wheel Diameter 3.5 Reduced Ride Quality Small wheels have not been specifically studied in this 3.5.1 Basic Causes research project because all the existing U. S. and Canadian The increased number of degrees of freedom of the center systems using this type of LFLRV have used a 26-inch wheel truck may allow additional dynamic modes to develop that and this is suitable for future applications in the United States. may affect ride quality. The primary suspension is usually The use of smaller wheels generates a range of additional stiffer than for conventional cars and is likely to have reduced issues because of travel. IRWs have a greater susceptibility to the formation of wheel flats, which, although they may not significantly affect · Higher tread contact stresses; ride, the noise generated can give passengers the impression · The need to ensure adequate guidance at obtuse crossings; that the vehicle is riding badly. Similarly, if passengers expe- · The lower available volume of wearable material; and rience more noise than on other cars, this may cause them to · Lower wheel inertia, leading to increased risk of wheel take more notice of ride discomfort. slide. If rail wear increases, which as stated in Section 3.3 may be the case with LFLRVs, corrugations generated must be dealt The smallest wheels known to be used in an IRW applica- with promptly, otherwise the ride will seem very poor and tion are of 550 mm (215/8 inch) diameter on a design used in may affect other cars using the system. Europe. Smaller wheels (400 mm/153/4 inches) are used on several LFLRV designs, but with wheels of such a small diameter it is 3.5.2 Experience with Ride Quality possible to create a low-floor design without the need for IRWs. None of those six transit authorities using LFLRVs that responded to the questionnaire saw ride quality as having Variation in Wheel Diameter on the Same Axle caused any serious issues. Where rough riding has been expe- rienced, it has usually not reached the point at which passen- IRWs steer by their wheel profile and the effects of gravity, gers have complained. so variations in wheel diameter on the same axle will not have the effect that might occur with conventional wheelsets. 3.5.3 Solutions Axle Parallelism The design must provide adequate suspension, despite the lack of space. The center section must be linked to the other Guidelines have been adopted in Europe in order to main- sections so as to allow the articulation to operate smoothly tain the parallelism of axles within limits (11). Practice there
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27 has suggested that halving the permitted out of parallelism Table 3-2. Rail sections and associated compared with conventional trucks gives an appropriate limit wheel tapers. for center trucks with IRWs. System Rail Wheel taper (1 in) Portland 115RE 30 Portland Ri59 30 3.6.2 Wheel Profile Parameters Newark 115RE 20 Hudson-Bergen 115RE 20 Wheel Profile/Rail Profile Match Santa Clara 115RE 32 Santa Clara Ri59 32 To minimize wear, it is necessary to ensure a good match San Diego 115RE 40 Houston 115RE 40 between wheel and rail profiles. The following characteristics Boston 115RE Formerly 40 now 20 are desirable: Boston 149GCR Formerly 40 now 20 · Absence of 2-point contact; · Smooth progressive movement of contact patch position Flange Angle on rail and wheel through the full range of wheelset lateral displacements; Traditional European tramway flange angles range from · Maximum width of contact patch to occur at low wheelset 76 to 78 degrees. More modern designs have reduced this to lateral displacement, to minimize contact stresses (and 70 degrees, while the European heavy rail standard is still hence wear) at the position where the wheelset will spend lower--typically at 68 degrees. The heavy rail freight standard most time; and in the United States is 75 degrees and passenger lines vary · Wheel and rail profiles to broadly retain the same shape as from 68 to 75 degrees. The Siemens cars used in Portland and they wear. Houston have 70-degree angles. In Boston, the original design on the Type 8 cars was 63 degrees, since modified to 75 degrees. The need to match wheel and rail profiles makes it unde- This latter angle is also used on the NJ TRANSIT cars and the sirable to have a mixture of significantly different wheel pro- Siemens Avanto. files operating on the same system. There will usually be slight Selection of flange angle is driven by two conflicting criteria: differences caused by different wear rates on a given new pro- file, but this is beneficial because it helps avoid rolling contact · Shallow flange angles are better for reducing flange wear. fatigue caused by uniform wear patterns. · Steep flange angles are better for resisting flange climbing All the above applies to any LRV; however, IRW cars of the derailments. type being studied are more sensitive to issues of wheel/rail profile matching because they generate higher lateral forces Shallower flange angles increase the risk of flange climbing and possibly higher angles of attack. The results of the mod- derailment caused by the reduced lateral force needed to eling carried out as part of this research, described in Appen- climb and by reducing the climb out distance once the criti- dix A, suggested that, in some cases, conventional LRVs may cal L/V limit is exceeded. generate higher angles of attack on the same track than Steeper flange angles can increase the risk of derailment on LFLRVs with IRW center trucks. sharp discontinuities in the gauge side of the rail, although Although issues are minimized if wheel and rail profiles are the flange-tip radius is also an important factor. A steeper compatible, this is not easy to achieve during a "transition" flange angle also causes more wear. stage (e.g., when new cars with new profiles are introduced to This conflict explains why heavy rail vehicles, which nego- an existing system). It is possible however as has been demon- tiate much larger radius curves than LRVs, generally have low strated in Zurich (10). flange angles (63 degrees typically) whereas LRVs generally Using more than one wheel profile on a system can affect have high angles of 70 to 75 degrees. However, a few systems, wheel-rail interaction adversely. Having one wheel profile where wear is considered the critical factor, are actually using on a system also facilitates profile maintenance; however, the relatively shallow angles (e.g., Berlin, 68.2 degrees, and wheel width and wheel back-to-back dimensions can be var- Zurich, 64 degrees). In both cases, these flange angles are used ied so that vehicles occupy the same space in the rail groove with 100-percent LFLRVs, although in Zurich the wheels are and in respect of the angle of attack on curves, thereby actively steered into the curves by an articulation-controlled allowing vehicles with different wheel base dimensions to be linkage, which limits the angle of attack. used. Table 3-2 shows wheel tapers that have been used with IRW cars of the type being studied will generate higher various rail profiles on the U.S. transit systems that use lateral forces and higher angles of attack compared with LFLRVs. conventional LRVs. These types of vehicle, therefore, require
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28 relatively high flange angles to ensure safety against derail- occur. It is not a critical parameter but the following consid- ment. erations apply: It would not be appropriate to state a fixed "optimum" flange angle, given that the selection for a particular car · Higher flanges give some protection against derailment. design should be based on the angle necessary to provide · The height of the flange will be limited by the depth of the minimum wear while giving safety against derailment and track groove. This depth is not only determined by the rail good matching to the local rail profile. section--it is also affected by rail head grinding, which On systems where a mixture of IRW and non-IRW cars tends to reduce the effective depth of the groove. Flange operates, the IRW cars probably will require the highest height selection, therefore, affects infrastructure mainte- flange angle. Ensuring that all cars on the system have a con- nance costs. sistent profile means that the non-IRW cars will need to · Higher flanges will tend to have thinner tips, which will be adopt the same profile--this is likely to have the following subject to increased wear if flange-tip running is practiced, consequences: although wear rate will decrease as the tapered flange gets lower. Modern vehicles, which tend to have higher axle · A change to the dynamic behavior/wear characteristics of loads, will be particularly affected. the non-IRW cars, which will, therefore, require reassess- ment; and The minimum allowed flange height in Germany is 18 mm · Less-than-optimum wear performance from the non-IRW 3 ( /4 inch). Good practice in that country is to never go below cars. 22 mm (0.87 inches) and to use a maximum of 24 mm (0.95 inches) on newly profiled wheels that will be subject to flange This issue has been discussed in TCRP Report 71, Volume 5 tip running, so as to allow for wear. But if a higher flange has (12), which noted the same range of angles in use and that a smaller flange-tip width, it might wear quickly with exten- recent guidance had proposed a minimum angle of 72 de- sive flange-tip running, losing this advantage. A balance is grees (+3 degrees, 2 degrees). This was proposed by APTA needed--the figures suggested represent such a compromise. (13). It was associated with a 1 in 20 tread taper and was to be With good track conditions, no flange-tip running, and flange achieved at the gauge point, 3/8 inch above the standard base height increasing caused by wheel wear with time, a mini- line. The basis was to establish a margin of safety above the mum value of 20 mm (0.9 inches) may be sufficient. 70 degrees previously considered sufficient. Table 3-3 summarizes the flange heights used on LFLRVs in the United States. Flange Height Tread Width In simple terms, the higher the flange, the lower the prob- ability of flange climbing derailment under extreme cir- The U.S. systems using LFLRVs use flange-tip running and, cumstances. However, it is often not possible to increase therefore, can use thinner wheels. Selection of tread width is flange height on an existing system that uses grooved rail or not considered to be influenced by whether or not a car has where flange clearance is limited. Increasing the flange IRW. It is mainly determined by the type of system on which height may affect wheel back-to-back dimensions, flange the cars will operate. Streetcars use narrow wheels (4 inches thickness, and wheel mass. To ensure safety at obtuse cross- typically) for the following reasons: ings, larger flanges are necessary when very small wheel diameters are used. · Many large-angle crossings requiring flange running--the With higher flanges, the flange-tip width reduces. A nar- outer part of the wheel tread is not used because of the rower flange tip is disadvantageous, if flange-tip running (i.e., where wheels run on the tips of their flanges, rather than the wheel treads) is used on track with flat grooves in Table 3-3. Flange heights. crossings and in switches with sharper angles, because the System Type of car Flange height contact stresses are higher and, hence, wheel and rail wear inches mm increases. MBTA 8 Type 8 0.75 (18) Portland MAX Siemens/Duewag 1.063 (27) The height of the wheel flange determines how long an NJT Kinki-Sharyo 0.75 (1) (18) (1) excessively high L/V ratio must be sustained before the vehi- San Jose, Santa Clara VTA Kinki-Sharyo/Alstom (1.063) 27 Houston/San Diego Siemens Avanto S70 (1.08) 27.3 cle derails. As such, wheel flange height is the last defense Notes: against derailment and, ideally, the vehicle-track interaction 1. To be changed to 1 inch (25.4 mm) should be designed so that excessive L/V conditions do not For explanation of the use of brackets in this table see Section 1.6.
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29 typical switch design where sharp curves require flange machine to simulate railway wheel/wear conditions produced running (so there is no tread contact). some interesting results (14): · Wider wheels may damage the surface of the adjacent high- way. · Lower strength rail steel wore less than high-strength rail steel when the same wheel material was used. LRVs use wider wheels (5 inches or more) for the follow- · Wheel wear was reduced by using softer rail material. ing reasons: · The increase in rail wear when using higher strength wheel steel was not as great as the wheel wear reduction. · Where there are limited or no flange running and small- · The reduction in wheel mass decreased with harder wheels. angle crossings, the outer part of the tread comes into con- tact with the rail because of the typical switch design for Therefore, using higher strength wheel material may have gentle curves where frogs are used in association with advantages and using higher strength rail material may not. check rails. The ratio of the yield strength to the tensile strength of the · Care is needed to avoid development of hollow tread wear materials used is also very important. Although the material and consequent damage to highway by the outer part of the may not fail (measured by its tensile strength), it may experi- tread. ence plastic deformation (related to yield strength), causing it to crack and wear rapidly. Table 3-4 shows the width of wheels used on the main sys- Rail and wear hardness are part of the much wider consid- tems studied; for explanation of the use of brackets in this eration of tribology, the science of wheel and rail wear, in table, see Section 1.6. which many other factors play a part. Tribology also consid- Standard AREMA frogs require a 5.25-inch-wide wheel. ers loading conditions, the micro and macro properties of These considerations suggest that wheel tread width materials, the influence of lubrication and dust at the inter- should be about 5.25 inches, unless flange-tip running is used face, and environmental conditions (e.g., humidity and con- throughout, in which case, tread width may be reduced to tamination). Relationships are complex and non-linear. 4 inches. A wider wheel can be accommodated on embedded track, provided the rail head is raised above the surrounding pavement. U.S. and Canadian standards allow this projection. 3.6.3 Other Vehicle Issues The width of the wheel has a minimal indirect effect on Configuration Issues performance issues and, in the case of derailment, the track can be designed to accommodate wheel width without this The angle of attack of a wheelset is defined as the angle issue arising. between the track radial line and the centerline of the wheelset axle. High angle of attack values will magnify many of the wheel-rail interface issues and create issues at switches Relative Hardness of the Wheel and the Rail and crossings. The truck design and the way it is attached to The relative hardness will affect wear rates. A "softer" wheel the body sections will affect the angle of attack; details of the is generally preferred, because it is easier to re-profile wheels suspension system will determine both the rate of change and than rails. The work hardening quality of the material is a the probability of extreme angles occurring. The angle of related factor (e.g., manganese steel performs well because it attack will also be influenced by the articulation design and work hardens when shock loads are applied). But manganese the truck wheelbase. steel may not be the best material for withstanding the more LFLRVs with center sections have been shown to have a usual sliding loads that arise at the wheel-rail interface. Tests fundamentally poorer dynamic performance than conven- carried out by the German Railways using a roller test tional two-section LRVs. In part, poorer performance arises because of the additional degrees of freedom that this type of vehicle possesses. The design of the center section must, Table 3-4. LFLRV wheel widths. therefore, control these extra degrees of freedom, allowing System Type of car Tread width sufficient flexibility while preventing the development of any inches mm oscillation modes. MBTA Type 8 4 (101.6) The modeling undertaken as part of the research showed Portland MAX Siemens/Duewag (4.96) 126 that two very different design solutions can perform almost NJT (Newark Subway) Kinki Sharyo 4 (101.6) equally well in practice. Table 3-5 shows how the various NJT (Hudson-Bergen) Kinki Sharyo (5.25) 133 San Jose, Santa Clara VTA Kinki Sharyo/ALSTOM (5.51) 140 modes of the center section are controlled in the two LFLRV Houston/San Diego Siemens Avanto S70 (5.31) 135 cars that were modeled.
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30 Table 3-5. Methods of controlling the movement of the center section. Mode of center section Kinki Sharyo LFLRV Breda Type 8 LFLRV Bounce 2 air bags 4 air bags Pitch Referenced to other sections by Z-link Referenced to truck by anti- and dampers pitch bar Roll Held rigid to other sections by design of Held rigid to other sections by articulation joints horizontal bars at roof level Yaw Not permitted relative to truck (locked) Some degree of freedom There is no particular advantage to any specific solution; higher lateral loads. Therefore, vertical wheel unloading must however, the design must address the issue of truck and be minimized in order to avoid a risk of derailment. The study wheelset alignment, because the absence of self-steering on of this is a standard part of any car design process. There is no the center truck will promote misalignment of the wheels evidence of issues in achieving the requirement. Two very dif- leading to wear, noise, and potentially an increase in derail- ferent solutions to the issue were studied in this research: ment risk. The following factors should be considered: · Conventional rubber/metal primary suspension and · Parallelism of the IRW wheelsets must be maintained as · Minimal primary suspension combined with a torsionally closely as possible. The effect of tolerance build-up within flexible bogie frame (as used on the MBTA Type 8 cars and the truck must be considered in the design. The design ide- described in Section 2.3.2). ally should prevent the alignment changing because of service wear or maintenance, but if this is not possible, the The solutions were found to perform equally well. Notably, maintenance instructions must include a requirement to the flexible frame studied did not have significantly higher check the wheelset alignment following overhaul of trucks unsprung mass than the conventional design. Typical stiff- and propose methods of reclamation. nesses will range from 500 N/mm to 1,000 N/mm (1.4 to · The effect of friction or asymmetries in center-section 2.8 tonf/inch), and lower values cause issues with rolling articulation linkages and/or dampers must be accounted behavior. Probably, the flexible frame would have poorer for in the design. These can lead to the car sections being noise and vibration isolation and potentially higher mainte- out of alignment on straight track. nance costs. It is a less well-proven solution. The conclusion of the modeling exercise was that the choice Total Side-To-Side Play Between the Truck Frame of articulation design as such has little overall effect on vehicle and Car Underframe performance. Performance is mainly influenced by the other factors mentioned in this section. The articulation design This is a secondary suspension issue. The horizontal stiff- should be chosen to suit the selected vehicle configuration. ness of the secondary suspension should have a progressively increasing stiffness gradient, and the rotational freedom about the vertical axis needs to be limited. The higher the Position of Secondary Suspension swiveling angle, the higher the torque moment induced by the In the modeling exercise, two arrangements of secondary longitudinal forces at the articulation. springs were studied: Maintaining the Vehicle in a Straight Line · Two springs at a central location on the truck (conven- During Braking tional) and · Four springs, one at each corner (unconventional). Maintaining the vehicle in a straight line during braking is desirable because it reduces the specific performance issues These arrangements were found to have equivalent being studied, keeps the vehicle within the permitted space, dynamic performance within the context of the overall vehi- and helps minimize the gaps at boarding points. Maintaining cle design. the vehicle in a straight line during braking can be achieved by controlling the braking rates on each articulated section. Braking IRWs is more difficult than braking conventional Primary Suspension Stiffness wheels because each wheel may react to the friction condi- IRW cars require better resistance to wheel unloading on tions on one rail and will not be affected by the other. A con- twisted track than non-IRW cars, because IRW cars generate ventional wheelset, which has more total mass, is less likely
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31 to seize. The sections can be kept in a straight line by braking The conclusion of this research is that systems mainly see the rear truck harder than the leading truck. At other times, the lubrication as a solution to the wheel squeal issue and con- traction applied to the leading truck can be slightly tributing, alongside other mitigation, to reduced wheel and more than to the trailing truck, so as to achieve the same rail wear. effect. Conditions that cause the center truck to swivel and cause issues are eliminated if its lateral play is reduced by 3.6.5 Track Parameters such methods. Data from the studied systems were collated in order to study the effect of flangeway clearance and track gauge vari- 3.6.4 Lubrication ations. The gap between the railhead and the wheel at gauge Table 3-6 gives an overall picture. All systems studied use measurement height and the equivalent figure between the track-mounted lubricators but have not generally provided back of the wheel and the restraint side of the groove in vehicle-mounted ones. The severity of the issues quoted embedded track were considered. The information was depends on individual judgment, but wheel wear seems to be assembled for tangent track only, because this will indicate the the most common issue being mitigated. Table 3-7 gives more extent to which the wheels on the center truck might be free detail of the track lubrication methods used. to move laterally or rotate about a vertical axis. In some of these applications, in particular San Diego The gauge may be narrowed on tangent track in order to and Boston, track lubrication exists, but has not been used reduce angle of attack, but if the gauge is excessively narrow, as a primary method of dealing with the issues associated a light wheelset might rise out of the track and derail, even with LFLRVs. In San Diego, only one car has been intro- with a steep flange angle. This has occurred with a vehicle of duced recently. The other systems gave reports on the effec- this type. Tight gauge conditions were caused by a combina- tiveness of trackside lubrication (both gauge face and top tion of the failure of an axle-end retaining nut on the vehicle of rail friction modifiers) in dealing with issues as described and the relatively narrow track gauge at the location. in Chapter 2. Adequate flangeway clearance is important in order to allow sufficient lateral wheelset displacement and, hence, allow steering by rolling radius difference for non-IRW rather Table 3-6. Use of lubrication to mitigate against than flange contact. A minimum clearance of 5 to 7 mm (0.2 performance problems. to 0.3 inches) is recommended. A nominal 9 mm (3/8 inch) would be suitable for ideal track conditions. The higher value System Lubrication system Problems experienced Track Vehicle Excessive Excessive Excessive Excessive is better in continuous track, so that the vehicle can adjust mounted mounted wheel track external internal without restraint. wear wear noise noise Newark Yes No Yes Yes No No On curves, the gauge may be widened because of the angle City of attack, but one needs to avoid the situation where the gap Subway Portland Yes No No No Yes No allows a wheel to hit the side of the rail with some force Santa Yes No No No Yes No Clara because, in certain situations, this will lead to damage and San Yes No No No No No possibly derailment. Also, care must be taken to avoid wheels Diego Houston Yes Yes Yes No No Yes being pinched between guards or girders when the gauge is Boston Yes Testing Yes Yes No Yes widened. Table 3-7. Details of lubrication systems used on U.S. transit systems using LFLRVs. System Grease Top friction Side Mitigating applicators modifiers friction Wheel Track Noise modifiers wear wear Newark City Yard turnouts On Penn Stn. Loop Sharp No Yes Yes Subway tracks curves Portland Sharp curves, Girder Yes Yes Yes rail, embedded track Sharp curves, Yes Yes Yes ballasted track Santa Clara Sharp curves No No Yes San Diego Sharp curves Existing lubrication, no problems with LFLRV as yet Houston Sharp curves Yes Yes Yes Boston Sharp curves No No Yes
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32 On IRW, steering by rolling radius difference does not The provision of tangent track in reverse curves is not a occur. Instead, some limited steering forces are generated particularly critical requirement for IRW cars. The tangent because of the different contact angles. Although this effect is track minimizes articulation angles, but three-section IRW small, it is important to ensure that flangeway clearance is not cars will generate lower articulation angles than two-section allowed to become too small such that the effect cannot cars for any given curve. Transition curves should be used as develop at all. well as the tangent track on reverse curves. It is possible to exploit the principle of asymmetric wheel profiles. The rail is ground on the running face to give an opti- Lateral Alignment Specifications for Track mum profile and on curves the profile ground onto on each rail may be different, in order to achieve the same effect. This The effects of poor lateral alignment will be more severe for principle has been used on the Santa Clara VTA system, where IRW vehicles, but modeling indicates that the issue is proba- LFLRVs are in use. bly related to ride, rather than a derailment risk. U.S. specifi- cations are comparable with European practice for low-floor cars; however, the method of application differs from Euro- 3.6.6 Other Track Features pean practice and this probably will lead to a lower standard Curve Radii of track than these cars may have been originally developed for (See Appendix E). The study considered the minimum curve radii appropri- ate for the specific type of vehicle being examined in this research (i.e., a three-section articulated vehicle with a center Track Twist trailing truck with IRW). This is not a critical factor for IRW, providing that existing IRW cars generate higher levels of lateral force and higher limits continue to be applied. angles of attack, which increase wear rates and the risk of derailment. This issue is made worse as curve radii reduce. Below 25 m, the angle of attack increases sharply--25 m is Issues Associated with Special Trackwork generally regarded as an advisable minimum for new track All the performance issues can arise from issues associated alignment (see Figure 3-1). with special trackwork but derailment is the most serious To minimize wear and noise and to improve ride, transi- because the risk is potentially increased, whereas issues with tion curves should be provided for IRW cars. This is necessary noise, wear, and ride can be mitigated, provided the principles because the body is rigidly fixed to the center truck and so the discussed elsewhere in this report are applied. In view of this, effect of changes of curvature will be magnified. A minimum the only issue that is specifically discussed here is that of transition length of 6 m (20 feet) is used in Germany and it derailment. would be appropriate to use this figure in the United States Table 3-8 summarizes all the identified LFLRV center and Canada for this configuration of LFLRV so as to ensure truck derailments on special trackwork that have taken place that this track condition is no worse. in the United States. Table 3-8 shows the circumstances and any mitigation that each system introduced following these incidents. Where these incidents have been caused by track defects, the mitigation has been either to improve track standards or to add further restraining measures. This is in line with the guidance provided in a previous report (15). In some cases, vehicle modifications occurred as well. Where the wheels on center trucks wear rapidly, the flanges become very thin and this increases the derailment risk on special trackwork. It is difficult to close switchblades precisely because of practical reasons; a tolerance of 3 mm (1/8 inch) is normal. IRWs need to be able to cope with this variation in order to ensure safe operation, especially if the design of the switch makes this critical. Figure 3-1. Example of angle of attack increasing The risk of derailment on switches can be minimized or with reducing curve radius. eliminated with various types of restraining and guardrail,
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33 Table 3-8. LFLRV center truck derailments on switches. System Vehicle Description Mitigation Newark City Kinki Sharyo Both axles of center truck derailed on House top protection Subway switches at low speed (three incidents added to switches 2001/2/4) Santa Clara Kinki 2003. Lead axle of center truck derailed None (Causes were Sharyo/ALSTOM on yard switch not vehicle or 2004. Both axles of center truck derailed infrastructure related) on switch at 5 mph. Boston Breda 2000. Leading axle of center truck Vehicle alignment derailed on reverse curve switch at corrections, additional 20 mph, running empty. restraining rails. 2001. Leading axle of center truck None derailed on curved switch at low speed. including house tops positioned above rail level to guide the · Adoption of standards for gauge face wear angles on switch backs of wheels and thereby prevent wheel flanges from split- and closure rails, and ting the switchblade from the rail (see Figures 3-2 through · Eliminating the mismatch between wheel and rail. 3-4). However, fully guarding can easily double the cost of a switch, itself a relatively expensive piece of equipment, so Because IRW trucks may generate high angles of attack and other solutions may be worth considering. For example, there high lateral forces, it is necessary to tightly control the accu- is the possibility of developing moveable frog switches for racy of positioning of switchblade tips to prevent the risk of transit applications--these might prove to be part of an opti- climbing. mum solution when IRWs are in general use (15). The possible need to provide more complex switches as a The report referred to above (15) concludes that derail- way of overcoming issues with LFLRVs has cost implications, ment risks can be minimized by adopting the following prac- which may significantly affect the business case for introduc- tices, which it then ranks, as shown, in order of effectiveness: ing them. · Lubrication, 3.6.7 Maintenance Standards · Development and implementation of maintenance and inspection standards, None of the maintenance standards of transit systems are subject to the Federal Railroad Administration processes, but are determined by the regulations that apply in each individ- ual state of the United States. Also, Federal regulations (including the new requirement [49 CFR Part 659]) will come into effect in 2006 that each state must designate an inde- pendent oversight agency. This will affect the application of maintenance standards because Section 19 is a requirement for a system safety plan that shall include maintenance plans with inspection periods and so forth. APTA published a Manual for Safety System Program Plans in 1991, significant parts of which will now be incorporated Figure 3-3. Enlargement of the house top area Figure 3-2. Fully guarded switch. showing guard rails either side.
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34 Table 3-9. Maintenance standards used by transit systems that have LFLRVs. System Notes NJT Has its own manual ("MW 4"). Portland Own specific requirements. Track is maintained to the suggested limits of the FTA guidance manual "Design Criteria" published in August 2002. Santa Clara Issued own procedures MTN-PR-6405. San Diego Applies FRA class 6 requirements--most of the initial route was part of the FRA-controlled general railway system of the United States. Houston Uses a maintenance manual. Boston Published its own track maintenance and safety standards for the Green Line in 2002. There does not appear to have been any standardization of maintenance relevant to LFLRVs--each system that has introduced them has had to develop its own requirements. Maintenance procedures will generally be followed if the instructions provided are clear and easy-to-follow. Table 3-9 shows which systems have their own standards and those published by one of these systems is a good example of this. The system's standards present the information in separate sections applicable to different situations and provide intro- ductory material that assists understanding and application and that can be the basis of staff training exercises. TCRP Report 71, Volume 5 (12) also notes the diversity of maintenance practices among transit operators and the con- sequent difficulty in establishing uniform guidelines. Track maintenance standards are likely to affect the fol- Figure 3-4. A house top with the guard rail on the lowing contributing factors to performance issues identified approach. in this study: in the regulations. The manual proposed that each transit sys- · Rail Profile. Certain wear patterns will cause the rail pro- tem should develop and manage its own maintenance plans. file to change. If the profile is not checked and corrected Also APTA published its Standard for Rail Transit Track regularly, this will cause issues. Inspection and Maintenance in 2002. This is a detailed docu- · Track Tolerances. If the track geometry is not maintained ment, but is only an advisory guideline. It covers embedded within tolerances, derailment and possibly other perform- streetcar track as well as ballasted track, but significantly ance issues will result. makes no mention of LFLRVs or vehicles with IRWs. In many · Lubrication. Wayside track lubrication systems need to areas, it recommends that transit systems create their own be maintained so that they function properly to reduce standards for the vehicle types used. noise and wear issues and to prevent excessive lubrica- Table 3-9 summarizes what the various transit systems tion, which creates excessive contamination of the consulted as part of this study have said about the mainte- roadbed and top of rail, potentially leading to extended nance standards issue. braking distances.