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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations. Washington, DC: The National Academies Press. doi: 10.17226/13841.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations. Washington, DC: The National Academies Press. doi: 10.17226/13841.
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Page 4
Page 5
Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations. Washington, DC: The National Academies Press. doi: 10.17226/13841.
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Page 5

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3CHAPTER 1 INTRODUCTION The objective of this project was to improve wheel/ rail interaction in transit systems by introducing flange climb derailment criteria and wheel/rail profile management and maintenance guidelines that can be applied to transit operations. 1.1 BACKGROUND A railroad train running along a track is one of the most complex dynamic systems in engineering due to the many nonlinear components in the system. In particular, the inter- action between wheel and rail is a very complicated nonlin- ear element in the railway system. Wheel and rail geometries, involving both cross sectional profiles and geometry along the moving direction with varying shapes due to wear, have a significant effect on vehicle dynamic performance and operating safety. The wheel/rail interaction in transit operations has its own special characteristics. Without the requirement for interop- erability, transit systems have adopted different wheel and rail profile standards for different reasons. Some of these standards are unique to a particular system. Older systems with long histories frequently have wheel and rail profile standards that were established many years ago. For some older systems, the reasons that specific profiles were adopted have been lost in time. Newer systems have generally selected the wheel/rail profiles based on the increased under- standing of wheel/rail interaction in recent years. Transit systems are usually operated in dense urban areas, which frequently results in lines that contain a large percent- age of curves or curves with small radii, which can increase wheel and rail wear and increase the potential for flange climb derailments. Transit systems also operate a wide range of vehicle types—such as those used in commuter rail service, heavy or rapid transit, and light rail vehicles—with a wide range of suspension designs and performance characteristics. Increasing operating speed and introducing new designs of vehicles have posed an even greater challenge for transit sys- tems to maintain and improve wheel/rail interaction. Considering the special features of transit operations, the purpose of this report is first to propose a general form of flange climb derailment criterion derived from wheel profiles applied in transit vehicles and, second, to provide the guidelines for applying the management and maintenance of wheel/rail profiles for transit operators. Due to the diversity among practices currently applied by different rail transit systems, it is not possible to set univer- sal rules that can be applied to all transit systems. However, it will be beneficial to recommend certain guidelines that transit operations can follow in their wheel and rail mainte- nance practice. Thus, some guidelines in this report are rather more conceptive than quantitative. The contents of this report were compiled as the result of a review of the literature pertaining to flange climb derail- ment, wheel/rail interaction and wheel/rail profiles; exten- sive research on the development of flange climb derailment criteria; the investigation on several representative transit systems; and the authors’ experiences on a number of proj- ects previously conducted in related fields. 1.2 STRUCTURE OF THIS REPORT This work was performed in two phases. In Phase I, the common problems and concerns related to wheel/rail profiles were defined through a survey conducted on representative transit systems. The preliminary flange climb derailment cri- teria, derived using the wheel profiles collected in the transit system survey, were proposed. Two reports were produced after the Phase I work and are presented as appendices: • Appendix A: Effect of Wheel/Rail Profiles and Wheel/ Rail Interaction on System Performance and Mainte- nance in Transit Operations, and • Appendix B: Investigation of Wheel Flange Climb Derailment Criteria for Transit Vehicles (Phase I Report). Section 1.3 of this report briefly summarizes the results of Phase I. In Phase II, the flange climb derailment criteria developed in the Phase I work were further validated by track test data. A general form of the criterion is proposed in this report. A report detailing the validation and development of the criteria, “Investigation of Wheel Flange Climb Derailment Criteria for Transit Vehicles (Phase II Report),” is attached as Appendix C.

The validated flange climb criteria are stated in Chapter 2 of this report with examples of applications in simulation and track test for evaluating flange climb derailment. In Phase II, the guidelines for applying to management and maintenance of wheel/rail profiles for transit operations were recommended based on the problems and concerns uncov- ered in the survey and current transit operations practices. Chapter 3 presents these guidelines. Chapter 4 is a glossary provided to help the reader better understand the technical terms used in this report relating to the flange climb criteria and the wheel/rail profile. 1.3 SUMMARY OF PHASE I WORK Onsite surveys were conducted at six representative tran- sit systems to investigate current practices and concerns related to wheel/rail profiles in transit operations. After com- piling the information received and analyzing wheel and rail profiles that were collected onsite, common problems and concerns related to wheel/rail profiles and wheel/rail interac- tion were identified. These are summarized below: • Adoption of low wheel flange angles can increase the risk of flange climb derailment. High flange angles above 72 degrees are strongly recommended to improve operational safety. • Rough surfaces from wheel truing can increase the risk of flange climb derailment. Smoothing the surface after wheel truing and lubrication could mitigate the problem considerably. • Introduction of new wheel and rail profiles needs to be carefully programmed for both wheel truing and rail grinding to achieve a smooth transition from old wheel/rail profiles to new profiles. • Independently rotating wheels can produce higher lat- eral forces and higher wheel/rail wear on curves with- out adequate control mechanisms. • Cylindrical wheels may reduce the risk of vehicle hunt- ing (lateral instability), but can have poor steering per- formance on curves. • Some wheel and rail profile combinations used in tran- sit operations were not systematically evaluated to ensure that they have good performance on both tan- gent track and curves under given vehicle and track conditions. • Severe two-point contact has been observed on the designed wheel/rail profile combinations at several tran- sit operations. This type of contact tends to produce poor steering on curves resulting in higher lateral force and higher rate of wheel/rail wear. • Track gage and restraining rails need to be carefully set on curves to allow sufficient usage of rolling radius dif- ference (RRD) generated and to mitigate high rail wear and lateral force. 4 • Wheel slide and wheel flats are an issue for almost every system, especially during the fall season. Although sev- eral technologies have been applied to lessen the prob- lem, more effective ones are needed. • Noise related to wheels and rails generally are caused by wheel screech/squeal, wheel impact, and rail corruga- tions. Lubrication and optimizing wheel/rail contact would help to mitigate these problems. • Friction management is a field that needs to be further explored. Application of lubrication is very limited in transit due to the complications related to wheel slide and wheel flats. • Reduction of wheel/rail wear can be achieved by opti- mization of wheel/rail profiles, properly designed truck primary suspension, improvement of track mainte- nance, and application of lubrication. • Without a wheel/rail profile measurement and docu- mentation program, transit operators will have difficulty reaching a high level of effectiveness and efficiency in wheel/rail operation and maintenance. • Further improvement of transit system personnel under- standing of wheel/rail profiles and interaction should be one of the strategic steps in system improvement. With better understanding of the basic concepts, vehicle/track operation and maintenance would be performed more effectively. Appendix A provides further information about the above issues. An investigation of wheel flange climb derailment criteria as applied to transit operation was conducted by extensive computer simulations using the wheel/rail profiles collected from several transit systems. Based on simulations of single wheelsets, preliminary lateral-to-vertical (L/V) ratio and climb-distance criteria for transit vehicle wheelsets were pro- posed. The proposed criteria were further validated through simulation of three types of transit vehicles. This research has been based on the methods previously used by the research team to develop flange climb derailment criteria for the North American freight railroads. The main conclusions drawn from this study are summarized below: • The single wheel L/V ratio required for flange climb derailment is determined by the wheel maximum flange angle, friction coefficient, and wheelset AOA. • The L/V ratio required for flange climb converges to Nadal’s value for AOA greater than 10 milliradians (mrad). For lower wheelset AOA, the wheel L/V ratio necessary for flange climb becomes progressively higher than Nadal’s value. • The distance required for flange climb derailment is determined by the L/V ratio, wheel maximum flange angle, wheel flange length, and wheelset AOA. • The flange-climb distance converges to a limiting value at higher AOA and higher L/V ratios. This limiting

value strongly correlates with wheel flange length. The longer the flange length, the longer the climb distance. For lower wheelset AOA, when the L/V ratio is high enough for the wheel to climb, the wheel-climb dis- tance for derailment becomes progressively longer than the proposed flange-climb-distance limit. The wheel- climb distance at lower wheelset AOA is mainly deter- mined by the maximum flange angle and L/V ratio. • Besides the flange contact angle, flange length also plays an important role in preventing derailment. The climb distance can be increased through use of higher wheel maximum flange angles and longer flange length. • The flanging wheel friction coefficient significantly affects the wheel L/V ratio required for flange climb. 5 The lower the friction coefficient, the higher the single wheel L/V ratio required. • For conventional solid wheelsets, a low, nonflanging wheel friction coefficient has a tendency to cause flange climb at a lower flanging wheel L/V ratio. Flange climb occurs over a shorter distance for the same flanging wheel L/V ratio. • For independently rotating wheelsets, the effect of non- flanging wheel friction coefficient is negligible because the longitudinal creep force vanishes. • Increasing vehicle speed increases the distance to climb. The Phase I report detailing this study of flange climb cri- teria is given in Appendix B.

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TRB’s Transit Cooperative Research Program (TCRP) Report 71, Track-Related Research, Vol. 5: Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations examines flange climb derailment criteria for transit vehicles that include lateral-to-vertical ratio limits and a corresponding flange-climb-distance limit. The report also includes guidance to transit agencies on wheel and rail maintenance practices.

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