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Center Truck Performance on Low-Floor Light Rail Vehicles (2006)

Chapter: Chapter 3 - Performance Issues and Causes

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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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Suggested Citation:"Chapter 3 - Performance Issues and Causes." National Academies of Sciences, Engineering, and Medicine. 2006. Center Truck Performance on Low-Floor Light Rail Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/14000.
×
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23 3.1 Overview Generally, performance issues will result from several causes rather than one particular cause. Possible solutions can be broadly divided into design or maintenance parame- ters and other measures. Solutions may relieve one per- formance issue but may create or worsen another—the inter-relationships between issues and solutions are very important. Which solutions will work or are appropriate will depend on specific vehicle and track design features and other characteristics of the transit system concerned. Solving performance issues is complex, and general solutions will not always be effective. Table 3-1 summarizes the measures identified in this research as appropriate for solving the main performance issues specified. The table distinguishes between types of solution in both the “parameters or other” classification and by type (i.e., vehicle, wheel profile, track and switches). This table illustrates the complexity of the inter-relationships involved. Sections 3.2 through 3.5 of this chapter discuss each of the main performance issues in turn. Information is given about the extent to which these issues have actually occurred in the United States and the types of vehicle and conditions involved. The causes and potential solutions are summarized. Section 3.6 gives more background on each of the contributory factors, based on the findings of this research. 3.2 Derailment 3.2.1 Basic Causes The two principal causes of derailment that can be man- aged through the design and maintenance of vehicles and track are flange climbing and track discontinuity. Flange climbing derailments occur when the wheel flange climbs up out of the rails (i.e., when the vertical forces holding the wheel down on the rail are exceeded by the lateral forces, causing the flange to climb for a long enough period for the wheel to clear the rail). This is expressed as the L/V (lateral load divided by vertical load) ratio. As will be explained, this situation can be caused by many factors. Track discontinuity derailments occur where the wheel flanges are insufficiently constrained by the track. Under nor- mal conditions, this might only occur on switches and cross- ings where there are gaps in the rails or irregularities in the rail contact surfaces or where moving parts may not be in their proper positions. The flange climbing derailment risk of IRWs will be slightly higher than for conventional wheelsets because of the increased lateral forces, the possibility of a higher angle of attack generated by IRWs, and the configuration of LFLRV being studied. Trucks with IRW center trucks are, therefore, fundamentally more susceptible to derailment and, as a result, their behavior can be strongly influenced by other fac- tors, which would normally be of only secondary importance for trucks with solid axles. Vehicle suppliers should allow for this behavior. Increased “sensitivity” may also mean that track standards have to be tighter than might be acceptable with more conventional vehicles. It is also generally recognized that the management of the wheel/rail interface is even more critical. 3.2.2. Experience with Derailments Of the derailments that have occurred in the United States since this type of LFLRV was introduced and which were noted in questionnaire responses, only the following resulted from these interface issues: • NJ TRANSIT Newark Subway 3 derailments All on switches. • MBTA Boston 11 derailments 4 on switches. C H A P T E R 3 Performance Issues and Causes

There has also been one derailment in Minneapolis (see sec- tion 2.3.6). 3.2.3 Solutions Strategies to manage the wheel-rail interface (e.g., opti- mizing the flange angle in combination with the rail profile in use) are essential to preventing flange climbing derailment. In addition it is necessary to manage other features of the vehi- cle that might increase the angle of attack. The wheel-rail interface is also the key to preventing track discontinuity derailments, but here the prevention of track discontinuity is clearly also critical. 3.3 Excessive Wheel and Rail Wear 3.3.1 Basic Causes For any type of LRV, wear will occur because localized high points on the wheel or rail profiles cause high contact stresses, because the rail is softer than the wheel material or vice versa, or because the loads on the contact area are extremely high. It is also possible for wear to occur as corrugations or for it to propagate more quickly because of wheel flats or localized track irregularities. High points will be eliminated if the wheel-rail interfaces match under all conditions. Relative hardness of wheel and rail can be managed so as to keep wear from this cause within acceptable limits. Certain conditions can increase contact area loads, including sharp curves. It is possible to reduce the conditions that create rail corruga- tions and wheel flats and to eliminate the track irregularities that cause most wear. The LFLRVs considered in this study may be more susceptible to wear because IRWs and the cen- ter truck configuration make it more difficult to manage the relative aspects of the wheel and rail at the interface. 3.3.2 Experience with Excessive Wheel and Rail Wear Excessive wheel and rail wear is a major issue for many light rail systems, and many new systems worldwide seem to have experienced this, regardless of the type of vehicles used. 24 Performance problem Derailment Wheel wear Rail wear Noise Ride Vehicle parameters Trailing truck wheelbase (Variations within limited space available on the center truck) Minimal effect Minimal effect Minimal effect No effect No effect Smaller wheel diameter/ wheel flange length Avoidable effect Increases Increases Increases No effect Variation in wheel diameter Minimal effect Minimal effect Minimal effect No effect Minimal effect Wheel parallelism Effects Effects Minimal effect Minimal effect No effect Wheel profile parameters Flange angle Effects Effects Minimal effect Minimal effect No effect Toe radius Effects No effect No effect No effect No effect Flange height Extra safety No effect No effect No effect No effect Tread width Avoidable effect Minimal effect Minimal effect Minimal effect No effect Blend radius Effects No effect No effect No effect No effect Flange thickness Indirect effect No effect No effect No effect No effect Tread radius/taper Effect Effect Effect Effect Effect Other vehicle features Center section fixing to truck Possibly minimal effect Possibly minimal effect Possibly minimal effect No effect No effect Position of secondary suspension Minimal effect No effect No effect No effect No effect Inter-body damping Effect Improves Improves Improves Improves Primary suspension stiffness Effect No effect No effect No effect Effect Use of flange tip running Reduces risk Effect Effect Effect No effect Lubrication Minimal effect Effect Effect Effect No effect Track parameters Gauge tolerances Effect Effect Effect Effect Effect Flangeway clearance Effect Effect Effect Effect No effect Other track features Use of tighter tangent track Effect Effect Effect Effect Effect Sharp curves Possibly Impact Impact Impact Possibly Gauge widening on curves Possibly Impact Impact Impact Possibly Tangent track between curves Possibly Possibly Possibly No effect No effect Use of restraining rail Effect Effect Effect Effect No effect Undercut switches Effect No effect Local effect Local effect Local effect Extra guard rails and house tops Extra safety No effect No effect No effect No effect Embedding rails No effect No effect No effect Effect No effect Flexible switches Effect No effect No effect No effect No effect Switch rail tip design Effect No effect No effect No effect No effect Table 3-1. Summary of measures.

Portland MAX has experienced higher LFLRV wheel flange wear on the center truck than on the motor trucks (Section 2.3.1). MBTA’s Green Line experienced rapid wheel wear on all trucks of the Type 8 cars, and experienced excessive rail wear on its very sharp curves from all cars (Section 2.3.2). The Newark Subway has had higher wheel wear on the center trucks of its LFLRV fleet than on the wheels of the motor trucks and has very high rail wear on sharp curves (Section 2.3.3). NJ TRANSIT’s Hudson-Bergen line, Santa Clara VTA, Houston Metro, and San Diego did not report issues in the questionnaire responses but, in some cases, it was too early to have observed this issue. 3.3.3 Solutions On the type of LFLRV being studied, the use of IRWs on a short articulated section introduces the risk of increased angle of attack. The wheel-rail interface is critical for all LRVs, but for these types of vehicle it is also necessary to control the relative position of wheel and rail more closely so as to over- come this “flexibility.” Measures that reduce wheel and rail vehicle wear (e.g., lubrication) are more likely to be required if this type of vehi- cle is used, and this may increase costs. For new systems, it is possible to avoid the extremes of track geometry that have caused these issues on older systems. 3.4 Noise 3.4.1 Basic Causes IRWs generate more noise on tangent track because their lack of any intrinsic steering ability allows rubbing flange contact to occur. The noise generated by this is likely to be particularly noticeable in the vehicle because of the proxim- ity of the floor to the noise source and the difficulty of pro- ducing a successfully noise-inhibiting design within the constraints of an LFLRV. The more complex body shape, with two floor heights, makes noise suppression more difficult, but this effect is hard to quantify. Noise can result from wheel-rail roughness and, therefore, can be a secondary effect of wheel-rail wear (see above); wheel-rail roughness includes track corrugations and the extreme condition of wheel flats. Rail roughness tends to dominate over wheel roughness. IRWs are more sensitive than conventional wheelsets to wheel flat development because adhesion during braking cannot be shared across an axle and because of the low rotational inertia of the wheels. For all rail vehicles, rolling noise (the inevitable but not sig- nificant base level noise) can be worsened by periodic grind- ing if such grinding does not achieve an adequately smooth rail surface. Rolling noise will also be affected by the support stiffness of the rails. If the rail head and wheel profile vary significantly, this will worsen rolling noise, but conformity can cause corrugations, generating noise issues as noted above. There is a relationship between the wheel-rail contact area and noise because of “contact stiffness,”but noise does not vary significantly over a large range of contact stiffness variation. Frequent truing of wheels will avoid issues in this area (10). In general, rails and wheels radiate noise. The ties tend to dominate at low frequencies, rail at mid-frequencies, and wheels at high frequencies. Resilient wheels will radiate less noise. The reflectivity of a surface is also important, so although ballasted track tends to radiate more noise because of the exposure of the rail web, the ballast tends to absorb this better than a smooth road surface. Corrugations may be more likely on light rail because of light contact patch loads and lack of variation in wheel diame- ter (but experience is that variation in wheel diameter worsens wear issues generally). Where corrugations occur, the ability of the wheel to follow the rail profile is critical in terms of noise, so suspension/truck stiffness becomes a contributory factor. All noise is significantly increased by resonance effects, so whatever can be done to reduce these will be important. Noise occurs on curved track because of the lateral slip of the wheel tread across the railhead and by contact between the wheel flange and the gauge face of the rail. Squeal or howl will be the only noticeable wheel-rail noise on sharply curved track because cars will be moving slowly. Such noise is likely to be an issue on older systems with curves, which are sharper than modern LRVs are usually designed for, and LFLRVs are the first modern cars to be introduced. Flange contact is important with IRWs because their lack of self-steering ability leads to the generation of high angles of attack, which in turn leads to higher noise levels being generated. Squeal is sustained non-linear wheel oscillation and will only occur if the damping capabilities of the wheel are poor. This is unlikely with modern designs of LFLRVs which, in common with other modern LRVs, are likely to use resilient wheels. Noise emanating from special trackwork can be significant, even though obviously localized. LFLRVs may be worse in this respect if they use significantly stiffer suspension than conventional vehicles. 3.4.2 Experience with Noise Traditional streetcar lines were characterized by noise; unfortunately, many new light rail systems have experienced noise issues, despite technical advances and effort at the design stage. The U.S. transit systems using LFLRVs, however, have not generally experienced any significant issues that can be directly related to the use of this type of car. MBTA and Houston Metro have experienced a noisy envi- ronment in the vehicles but have either found solutions or 25

consider it to be within acceptable limits. Santa Clara VTA noted issues with wheel squeal on both high-floor and low- floor cars but consider that, in both cases, the noise does not exceed limits. In general, systems may have issues, perhaps only at certain locations, but they have been able to manage them effectively. 3.4.3 Solutions In general, noise can be reduced on tangent track by main- taining rail smoothness. The use of resilient wheels and other forms of damping may reduce squeal on curves but not nec- essarily eliminate it. Squeal may be controlled by use of lubri- cants or possibly using different metals for the wheels and rails, although the latter theory has not been fully tested. The use of special trackwork designed to reduce the risk of derailment with LFLRVs will probably have the added bene- fit of reducing noise associated with this type of track, assum- ing that discontinuities are eliminated. 3.5 Reduced Ride Quality 3.5.1 Basic Causes The increased number of degrees of freedom of the center truck may allow additional dynamic modes to develop that may affect ride quality. The primary suspension is usually stiffer than for conventional cars and is likely to have reduced travel. IRWs have a greater susceptibility to the formation of wheel flats, which, although they may not significantly affect ride, the noise generated can give passengers the impression that the vehicle is riding badly. Similarly, if passengers expe- rience more noise than on other cars, this may cause them to take more notice of ride discomfort. If rail wear increases, which as stated in Section 3.3 may be the case with LFLRVs, corrugations generated must be dealt with promptly, otherwise the ride will seem very poor and may affect other cars using the system. 3.5.2 Experience with Ride Quality None of those six transit authorities using LFLRVs that responded to the questionnaire saw ride quality as having caused any serious issues. Where rough riding has been expe- rienced, it has usually not reached the point at which passen- gers have complained. 3.5.3 Solutions The design must provide adequate suspension, despite the lack of space. The center section must be linked to the other sections so as to allow the articulation to operate smoothly without jerks, pitching, or yawing. The wheel tread profile is critical. If uneven wear occurs, the variation in wheel profile will cause a poor ride, so variations in wheel profile need to be kept within tolerance limits. The track quality needs to be high in terms of gauge and other variations. 3.6 Contributing Factors 3.6.1 Vehicle Parameters Truck Wheelbase The main effect of varying the center truck wheelbase would be to increase the critical angle of attack on very sharp curves. The angle of attack would typically be 2.5 degrees on a 25-m (82-ft) curve for a 1.9-m (6 ft 23⁄4 in.) truck and would change by about 0.1 degree for each 50-mm (2-in.) longer or shorter wheelbase dimension. Therefore, the effect is very slight. In practice, there is very little variation among vehicle designs. Wheel Diameter Small wheels have not been specifically studied in this research project because all the existing U. S. and Canadian systems using this type of LFLRV have used a 26-inch wheel and this is suitable for future applications in the United States. The use of smaller wheels generates a range of additional issues because of • Higher tread contact stresses; • The need to ensure adequate guidance at obtuse crossings; • The lower available volume of wearable material; and • Lower wheel inertia, leading to increased risk of wheel slide. The smallest wheels known to be used in an IRW applica- tion are of 550 mm (215⁄8 inch) diameter on a design used in Europe. Smaller wheels (400 mm/153⁄4 inches) are used on several LFLRV designs, but with wheels of such a small diameter it is possible to create a low-floor design without the need for IRWs. Variation in Wheel Diameter on the Same Axle IRWs steer by their wheel profile and the effects of gravity, so variations in wheel diameter on the same axle will not have the effect that might occur with conventional wheelsets. Axle Parallelism Guidelines have been adopted in Europe in order to main- tain the parallelism of axles within limits (11). Practice there 26

has suggested that halving the permitted out of parallelism compared with conventional trucks gives an appropriate limit for center trucks with IRWs. 3.6.2 Wheel Profile Parameters Wheel Profile/Rail Profile Match To minimize wear, it is necessary to ensure a good match between wheel and rail profiles. The following characteristics are desirable: • Absence of 2-point contact; • Smooth progressive movement of contact patch position on rail and wheel through the full range of wheelset lateral displacements; • Maximum width of contact patch to occur at low wheelset lateral displacement, to minimize contact stresses (and hence wear) at the position where the wheelset will spend most time; and • Wheel and rail profiles to broadly retain the same shape as they wear. The need to match wheel and rail profiles makes it unde- sirable to have a mixture of significantly different wheel pro- files operating on the same system. There will usually be slight differences caused by different wear rates on a given new pro- file, but this is beneficial because it helps avoid rolling contact fatigue caused by uniform wear patterns. All the above applies to any LRV; however, IRW cars of the type being studied are more sensitive to issues of wheel/rail profile matching because they generate higher lateral forces and possibly higher angles of attack. The results of the mod- eling carried out as part of this research, described in Appen- dix A, suggested that, in some cases, conventional LRVs may generate higher angles of attack on the same track than LFLRVs with IRW center trucks. Although issues are minimized if wheel and rail profiles are compatible, this is not easy to achieve during a “transition” stage (e.g., when new cars with new profiles are introduced to an existing system). It is possible however as has been demon- strated in Zurich (10). Using more than one wheel profile on a system can affect wheel-rail interaction adversely. Having one wheel profile on a system also facilitates profile maintenance; however, the wheel width and wheel back-to-back dimensions can be var- ied so that vehicles occupy the same space in the rail groove and in respect of the angle of attack on curves, thereby allowing vehicles with different wheel base dimensions to be used. Table 3-2 shows wheel tapers that have been used with various rail profiles on the U.S. transit systems that use LFLRVs. Flange Angle Traditional European tramway flange angles range from 76 to 78 degrees. More modern designs have reduced this to 70 degrees, while the European heavy rail standard is still lower—typically at 68 degrees. The heavy rail freight standard in the United States is 75 degrees and passenger lines vary from 68 to 75 degrees. The Siemens cars used in Portland and Houston have 70-degree angles. In Boston, the original design on the Type 8 cars was 63 degrees, since modified to 75 degrees. This latter angle is also used on the NJ TRANSIT cars and the Siemens Avanto. Selection of flange angle is driven by two conflicting criteria: • Shallow flange angles are better for reducing flange wear. • Steep flange angles are better for resisting flange climbing derailments. Shallower flange angles increase the risk of flange climbing derailment caused by the reduced lateral force needed to climb and by reducing the climb out distance once the criti- cal L/V limit is exceeded. Steeper flange angles can increase the risk of derailment on sharp discontinuities in the gauge side of the rail, although the flange-tip radius is also an important factor. A steeper flange angle also causes more wear. This conflict explains why heavy rail vehicles, which nego- tiate much larger radius curves than LRVs, generally have low flange angles (63 degrees typically) whereas LRVs generally have high angles of 70 to 75 degrees. However, a few systems, where wear is considered the critical factor, are actually using relatively shallow angles (e.g., Berlin, 68.2 degrees, and Zurich, 64 degrees). In both cases, these flange angles are used with 100-percent LFLRVs, although in Zurich the wheels are actively steered into the curves by an articulation-controlled linkage, which limits the angle of attack. IRW cars of the type being studied will generate higher lateral forces and higher angles of attack compared with conventional LRVs. These types of vehicle, therefore, require 27 System Rail Wheel taper (1 in) Portland 115RE 30 Portland Ri59 30 Newark 115RE 20 Hudson-Bergen 115RE 20 Santa Clara 115RE 32 Santa Clara Ri59 32 San Diego 115RE 40 Houston 115RE 40 Boston 115RE Formerly 40 now 20 Boston 149GCR Formerly 40 now 20 Table 3-2. Rail sections and associated wheel tapers.

relatively high flange angles to ensure safety against derail- ment. It would not be appropriate to state a fixed “optimum” flange angle, given that the selection for a particular car design should be based on the angle necessary to provide minimum wear while giving safety against derailment and good matching to the local rail profile. On systems where a mixture of IRW and non-IRW cars operates, the IRW cars probably will require the highest flange angle. Ensuring that all cars on the system have a con- sistent profile means that the non-IRW cars will need to adopt the same profile—this is likely to have the following consequences: • A change to the dynamic behavior/wear characteristics of the non-IRW cars, which will, therefore, require reassess- ment; and • Less-than-optimum wear performance from the non-IRW cars. This issue has been discussed in TCRP Report 71, Volume 5 (12), which noted the same range of angles in use and that recent guidance had proposed a minimum angle of 72 de- grees (+3 degrees, 2 degrees). This was proposed by APTA (13). It was associated with a 1 in 20 tread taper and was to be achieved at the gauge point, 3⁄8 inch above the standard base line. The basis was to establish a margin of safety above the 70 degrees previously considered sufficient. Flange Height In simple terms, the higher the flange, the lower the prob- ability of flange climbing derailment under extreme cir- cumstances. However, it is often not possible to increase flange height on an existing system that uses grooved rail or where flange clearance is limited. Increasing the flange height may affect wheel back-to-back dimensions, flange thickness, and wheel mass. To ensure safety at obtuse cross- ings, larger flanges are necessary when very small wheel diameters are used. With higher flanges, the flange-tip width reduces. A nar- 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 crossings and in switches with sharper angles, because the contact stresses are higher and, hence, wheel and rail wear increases. The height of the wheel flange determines how long an excessively high L/V ratio must be sustained before the vehi- cle derails. As such, wheel flange height is the last defense against derailment and, ideally, the vehicle-track interaction should be designed so that excessive L/V conditions do not occur. It is not a critical parameter but the following consid- erations apply: • Higher flanges give some protection against derailment. • The height of the flange will be limited by the depth of the track groove. This depth is not only determined by the rail section—it is also affected by rail head grinding, which tends to reduce the effective depth of the groove. Flange height selection, therefore, affects infrastructure mainte- nance costs. • Higher flanges will tend to have thinner tips, which will be subject to increased wear if flange-tip running is practiced, although wear rate will decrease as the tapered flange gets lower. Modern vehicles, which tend to have higher axle loads, will be particularly affected. The minimum allowed flange height in Germany is 18 mm (3⁄4 inch). Good practice in that country is to never go below 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 tip running, so as to allow for wear. But if a higher flange has a smaller flange-tip width, it might wear quickly with exten- sive flange-tip running, losing this advantage. A balance is needed—the figures suggested represent such a compromise. With good track conditions, no flange-tip running, and flange height increasing caused by wheel wear with time, a mini- mum value of 20 mm (0.9 inches) may be sufficient. Table 3-3 summarizes the flange heights used on LFLRVs in the United States. Tread Width The U.S. systems using LFLRVs use flange-tip running and, therefore, can use thinner wheels. Selection of tread width is not considered to be influenced by whether or not a car has IRW. It is mainly determined by the type of system on which the cars will operate. Streetcars use narrow wheels (4 inches typically) for the following reasons: • Many large-angle crossings requiring flange running—the outer part of the wheel tread is not used because of the 28 Flange height System Type of car inches mm MBTA 8 Portland MAX NJT San Jose, Santa Clara VTA Houston/San Diego Type 8 Siemens/Duewag Kinki-Sharyo Kinki-Sharyo/Alstom Siemens Avanto S70 0.75 1.063 0.75 (1) (1.063) (1.08) (18) (27) (18) (1) 27 27.3 Table 3-3. Flange heights. Notes: 1. To be changed to 1 inch (25.4 mm) For explanation of the use of brackets in this table see Section 1.6.

typical switch design where sharp curves require flange running (so there is no tread contact). • Wider wheels may damage the surface of the adjacent high- way. LRVs use wider wheels (5 inches or more) for the follow- ing reasons: • Where there are limited or no flange running and small- angle crossings, the outer part of the tread comes into con- tact with the rail because of the typical switch design for gentle curves where frogs are used in association with check rails. • Care is needed to avoid development of hollow tread wear and consequent damage to highway by the outer part of the tread. Table 3-4 shows the width of wheels used on the main sys- tems studied; for explanation of the use of brackets in this table, see Section 1.6. Standard AREMA frogs require a 5.25-inch-wide wheel. These considerations suggest that wheel tread width should be about 5.25 inches, unless flange-tip running is used throughout, in which case, tread width may be reduced to 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. The width of the wheel has a minimal indirect effect on performance issues and, in the case of derailment, the track can be designed to accommodate wheel width without this issue arising. Relative Hardness of the Wheel and the Rail The relative hardness will affect wear rates. A “softer”wheel is generally preferred, because it is easier to re-profile wheels than rails. The work hardening quality of the material is a related factor (e.g., manganese steel performs well because it work hardens when shock loads are applied). But manganese steel may not be the best material for withstanding the more usual sliding loads that arise at the wheel-rail interface. Tests carried out by the German Railways using a roller test machine to simulate railway wheel/wear conditions produced some interesting results (14): • Lower strength rail steel wore less than high-strength rail steel when the same wheel material was used. • Wheel wear was reduced by using softer rail material. • The increase in rail wear when using higher strength wheel steel was not as great as the wheel wear reduction. • The reduction in wheel mass decreased with harder wheels. Therefore, using higher strength wheel material may have advantages and using higher strength rail material may not. The ratio of the yield strength to the tensile strength of the materials used is also very important. Although the material may not fail (measured by its tensile strength), it may experi- ence plastic deformation (related to yield strength), causing it to crack and wear rapidly. Rail and wear hardness are part of the much wider consid- eration of tribology, the science of wheel and rail wear, in which many other factors play a part. Tribology also consid- ers loading conditions, the micro and macro properties of materials, the influence of lubrication and dust at the inter- face, and environmental conditions (e.g., humidity and con- tamination). Relationships are complex and non-linear. 3.6.3 Other Vehicle Issues Configuration Issues The angle of attack of a wheelset is defined as the angle 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 and crossings. The truck design and the way it is attached to the body sections will affect the angle of attack; details of the suspension system will determine both the rate of change and the probability of extreme angles occurring. The angle of attack will also be influenced by the articulation design and the truck wheelbase. LFLRVs with center sections have been shown to have a fundamentally poorer dynamic performance than conven- 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, therefore, control these extra degrees of freedom, allowing sufficient flexibility while preventing the development of any oscillation modes. The modeling undertaken as part of the research showed that two very different design solutions can perform almost equally well in practice. Table 3-5 shows how the various modes of the center section are controlled in the two LFLRV cars that were modeled. 29 Tread width System Type of car inches mm MBTA Type 8 4 (101.6) Portland MAX Siemens/Duewag (4.96) 126 NJT (Newark Subway) Kinki Sharyo 4 (101.6) NJT (Hudson-Bergen) Kinki Sharyo (5.25) 133 (5.31) 135 (5.51) 140 San Jose, Santa Clara VTA Kinki Sharyo/ALSTOM Houston/San Diego Siemens Avanto S70 Table 3-4. LFLRV wheel widths.

There is no particular advantage to any specific solution; however, the design must address the issue of truck and wheelset alignment, because the absence of self-steering on the center truck will promote misalignment of the wheels leading to wear, noise, and potentially an increase in derail- ment risk. The following factors should be considered: • Parallelism of the IRW wheelsets must be maintained as closely as possible. The effect of tolerance build-up within the truck must be considered in the design. The design ide- ally should prevent the alignment changing because of service wear or maintenance, but if this is not possible, the maintenance instructions must include a requirement to check the wheelset alignment following overhaul of trucks and propose methods of reclamation. • The effect of friction or asymmetries in center-section articulation linkages and/or dampers must be accounted for in the design. These can lead to the car sections being out of alignment on straight track. The conclusion of the modeling exercise was that the choice of articulation design as such has little overall effect on vehicle performance. Performance is mainly influenced by the other factors mentioned in this section. The articulation design should be chosen to suit the selected vehicle configuration. Position of Secondary Suspension In the modeling exercise, two arrangements of secondary springs were studied: • Two springs at a central location on the truck (conven- tional) and • Four springs, one at each corner (unconventional). These arrangements were found to have equivalent dynamic performance within the context of the overall vehi- cle design. Primary Suspension Stiffness IRW cars require better resistance to wheel unloading on twisted track than non-IRW cars, because IRW cars generate higher lateral loads. Therefore, vertical wheel unloading must be minimized in order to avoid a risk of derailment. The study of this is a standard part of any car design process. There is no evidence of issues in achieving the requirement. Two very dif- ferent solutions to the issue were studied in this research: • Conventional rubber/metal primary suspension and • Minimal primary suspension combined with a torsionally flexible bogie frame (as used on the MBTA Type 8 cars and described in Section 2.3.2). The solutions were found to perform equally well. Notably, the flexible frame studied did not have significantly higher unsprung mass than the conventional design. Typical stiff- nesses will range from 500 N/mm to 1,000 N/mm (1.4 to 2.8 tonf/inch), and lower values cause issues with rolling behavior. Probably, the flexible frame would have poorer noise and vibration isolation and potentially higher mainte- nance costs. It is a less well-proven solution. Total Side-To-Side Play Between the Truck Frame and Car Underframe This is a secondary suspension issue. The horizontal stiff- 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 swiveling angle, the higher the torque moment induced by the longitudinal forces at the articulation. Maintaining the Vehicle in a Straight Line During Braking Maintaining the vehicle in a straight line during braking is desirable because it reduces the specific performance issues being studied, keeps the vehicle within the permitted space, and helps minimize the gaps at boarding points. Maintaining 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 wheels because each wheel may react to the friction condi- tions on one rail and will not be affected by the other. A con- ventional wheelset, which has more total mass, is less likely 30 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 and dampers Referenced to truck by anti- pitch bar Roll Held rigid to other sections by design of articulation joints Held rigid to other sections by horizontal bars at roof level Yaw Not permitted relative to truck (locked) Some degree of freedom Table 3-5. Methods of controlling the movement of the center section.

to seize. The sections can be kept in a straight line by braking the rear truck harder than the leading truck.At other times, the traction applied to the leading truck can be slightly more than to the trailing truck, so as to achieve the same effect. Conditions that cause the center truck to swivel and cause issues are eliminated if its lateral play is reduced by such methods. 3.6.4 Lubrication Table 3-6 gives an overall picture. All systems studied use track-mounted lubricators but have not generally provided vehicle-mounted ones. The severity of the issues quoted depends on individual judgment, but wheel wear seems to be the most common issue being mitigated. Table 3-7 gives more detail of the track lubrication methods used. In some of these applications, in particular San Diego and Boston, track lubrication exists, but has not been used as a primary method of dealing with the issues associated with LFLRVs. In San Diego, only one car has been intro- duced recently. The other systems gave reports on the effec- tiveness of trackside lubrication (both gauge face and top of rail friction modifiers) in dealing with issues as described in Chapter 2. The conclusion of this research is that systems mainly see lubrication as a solution to the wheel squeal issue and con- tributing, alongside other mitigation, to reduced wheel and rail wear. 3.6.5 Track Parameters Data from the studied systems were collated in order to study the effect of flangeway clearance and track gauge vari- ations. The gap between the railhead and the wheel at gauge measurement height and the equivalent figure between the back of the wheel and the restraint side of the groove in embedded track were considered. The information was assembled for tangent track only, because this will indicate the extent to which the wheels on the center truck might be free to move laterally or rotate about a vertical axis. The gauge may be narrowed on tangent track in order to reduce angle of attack, but if the gauge is excessively narrow, a light wheelset might rise out of the track and derail, even with a steep flange angle. This has occurred with a vehicle of this type. Tight gauge conditions were caused by a combina- tion of the failure of an axle-end retaining nut on the vehicle and the relatively narrow track gauge at the location. 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 than flange contact. A minimum clearance of 5 to 7 mm (0.2 to 0.3 inches) is recommended. A nominal 9 mm (3⁄8 inch) would be suitable for ideal track conditions. The higher value is better in continuous track, so that the vehicle can adjust without restraint. On curves, the gauge may be widened because of the angle of attack, but one needs to avoid the situation where the gap allows a wheel to hit the side of the rail with some force because, in certain situations, this will lead to damage and possibly derailment. Also, care must be taken to avoid wheels being pinched between guards or girders when the gauge is widened. 31 Lubrication system Problems experienced System Track mounted Vehicle mounted Excessive wheel wear Excessive track wear Excessive external noise Excessive internal noise Newark City Subway Yes Yes Yes No Portland Yes Yes No Santa Clara Yes Yes No San Diego Yes Houston Yes Yes No Yes Boston Yes No No No No No No No No No No No No No No Yes Testing Yes Yes No Yes Mitigating System Grease applicators Top friction modifiers Side friction modifiers Wheel wear Track wear Noise Newark City Subway Yard turnouts On Penn Stn. Loop tracks Sharp curves No Yes Yes Sharp curves, Girder rail, embedded track Yes Yes Yes Portland Sharp curves, ballasted track Yes Yes Yes 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 Table 3-6. Use of lubrication to mitigate against performance problems. Table 3-7. Details of lubrication systems used on U.S. transit systems using LFLRVs.

On IRW, steering by rolling radius difference does not occur. Instead, some limited steering forces are generated because of the different contact angles. Although this effect is small, it is important to ensure that flangeway clearance is not allowed to become too small such that the effect cannot develop at all. It is possible to exploit the principle of asymmetric wheel profiles. The rail is ground on the running face to give an opti- mum profile and on curves the profile ground onto on each rail may be different, in order to achieve the same effect. This principle has been used on the Santa Clara VTA system, where LFLRVs are in use. 3.6.6 Other Track Features Curve Radii 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 trailing truck with IRW). IRW cars generate higher levels of lateral force and higher 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 generally regarded as an advisable minimum for new track alignment (see Figure 3-1). To minimize wear and noise and to improve ride, transi- tion curves should be provided for IRW cars. This is necessary because the body is rigidly fixed to the center truck and so the effect of changes of curvature will be magnified. A minimum transition length of 6 m (20 feet) is used in Germany and it would be appropriate to use this figure in the United States and Canada for this configuration of LFLRV so as to ensure that this track condition is no worse. The provision of tangent track in reverse curves is not a particularly critical requirement for IRW cars. The tangent track minimizes articulation angles, but three-section IRW cars will generate lower articulation angles than two-section cars for any given curve. Transition curves should be used as well as the tangent track on reverse curves. Lateral Alignment Specifications for Track The effects of poor lateral alignment will be more severe for IRW vehicles, but modeling indicates that the issue is proba- 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- pean practice and this probably will lead to a lower standard of track than these cars may have been originally developed for (See Appendix E). Track Twist This is not a critical factor for IRW, providing that existing limits continue to be applied. Issues Associated with Special Trackwork All the performance issues can arise from issues associated with special trackwork but derailment is the most serious because the risk is potentially increased, whereas issues with noise, wear, and ride can be mitigated, provided the principles discussed elsewhere in this report are applied. In view of this, the only issue that is specifically discussed here is that of derailment. Table 3-8 summarizes all the identified LFLRV center truck derailments on special trackwork that have taken place 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. The risk of derailment on switches can be minimized or eliminated with various types of restraining and guardrail, 32 Figure 3-1. Example of angle of attack increasing with reducing curve radius.

including house tops positioned above rail level to guide the backs of wheels and thereby prevent wheel flanges from split- ting the switchblade from the rail (see Figures 3-2 through 3-4). However, fully guarding can easily double the cost of a switch, itself a relatively expensive piece of equipment, so other solutions may be worth considering. For example, there is the possibility of developing moveable frog switches for transit applications—these might prove to be part of an opti- mum solution when IRWs are in general use (15). The report referred to above (15) concludes that derail- ment risks can be minimized by adopting the following prac- tices, which it then ranks, as shown, in order of effectiveness: • Lubrication, • Development and implementation of maintenance and inspection standards, • Adoption of standards for gauge face wear angles on switch and closure rails, and • Eliminating the mismatch between wheel and rail. Because IRW trucks may generate high angles of attack and high lateral forces, it is necessary to tightly control the accu- racy of positioning of switchblade tips to prevent the risk of climbing. The possible need to provide more complex switches as a way of overcoming issues with LFLRVs has cost implications, which may significantly affect the business case for introduc- ing them. 3.6.7 Maintenance 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 33 Figure 3-3. Enlargement of the house top area showing guard rails either side.Figure 3-2. Fully guarded switch. System Vehicle Description Mitigation Newark City Subway Kinki Sharyo switches at low speed (three incidents 2001/2/4) House top protection added to switches 2003. Lead axle of center truck derailed on yard switch Santa Clara Kinki Sharyo/ALSTOM 2004. Both axles of center truck derailed on switch at 5 mph. None (Causes were not vehicle or infrastructure related) 2000. Leading axle of center truck derailed on reverse curve switch at 20 mph, running empty. Vehicle alignment corrections, additional restraining rails. Boston Breda 2001. Leading axle of center truck derailed on curved switch at low speed. None Both axles of center truck derailed on Table 3-8. LFLRV center truck derailments on switches.

in the regulations. The manual proposed that each transit sys- tem should develop and manage its own maintenance plans. Also APTA published its Standard for Rail Transit Track Inspection and Maintenance in 2002. This is a detailed docu- ment, but is only an advisory guideline. It covers embedded streetcar track as well as ballasted track, but significantly makes no mention of LFLRVs or vehicles with IRWs. In many areas, it recommends that transit systems create their own standards for the vehicle types used. Table 3-9 summarizes what the various transit systems consulted as part of this study have said about the mainte- nance standards issue. 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- lowing contributing factors to performance issues identified in this study: • Rail Profile. Certain wear patterns will cause the rail pro- file to change. If the profile is not checked and corrected regularly, this will cause issues. • Track Tolerances. If the track geometry is not maintained within tolerances, derailment and possibly other perform- ance issues will result. • Lubrication. Wayside track lubrication systems need to be maintained so that they function properly to reduce noise and wear issues and to prevent excessive lubrica- tion, which creates excessive contamination of the roadbed and top of rail, potentially leading to extended braking distances. 34 Figure 3-4. A house top with the guard rail on the approach. 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. Table 3-9. Maintenance standards used by transit systems that have LFLRVs.

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Center Truck Performance on Low-Floor Light Rail Vehicles Get This Book
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TRB's Transit Cooperative Research Program (TCRP) Report 114: Center Truck Performance on Low-Floor Light Rail Vehicles examines performance issues observed in the operation of low-floor light rail vehicle (LFLRV) center trucks (focusing on 70-percent low-floor vehicles), such as excessive wheel wear and noise and occasional derailments, and provides proposed guidance on how to minimize or avoid these issues. The report also includes suggestions on LFLRV specifications, maintenance, and design, as well as on related infrastructure design and maintenance, to maximize performance of these LFLRV center trucks.

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