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1 SUMMARY Center Truck Performance on Low-Floor Light Rail Vehicles The purpose of this research was to help introduce low-floor light rail vehicles (LFLRVs) to the United States and Canada. Some LFLRVs that use unpowered wheels on stub axles on the articulated center section experience problems with excessive wheel wear and derailments. Vehi- cles of this type operate in transit systems in several cities in the United States, Europe and Aus- tralia; the success of these vehicles has been varied. The research was commissioned in order to better understand the performance of these cen- ter trucks, to compile lessons learned to date and to provide guidance to transit agencies and LFLRV manufacturers in mitigating problems associated with this type of vehicle. This report concentrates on these objectives and provides the associated guidance. The work involved a literature review, consultation with transit systems (via a questionnaire and visits), the identification of contributory factors, and modeling to assess their relative impor- tance. The guidance produced was structured so as to facilitate its use by different sectors of industry, for different applications over a long time. The topic is complex and the guidance sets the research findings in the context within which they will be used. Although performance problems including derailment, excessive wheel and rail wear, and noise and poor ride quality have arisen with these vehicles in the United States, corrective action has been taken and performance has improved. Despite this, the solutions adopted to date may not be the optimum ones for a "new start" system. The guidance presented in this report is based on the results of the previous corrective action, wider experience, and the work carried out dur- ing the research project. Performance problems are more likely to occur when these vehicles are introduced to a long- established transit system, where the track geometry and other conditions may be more challeng- ing for innovative vehicle designs. The guidance suggests that it may be necessary to modify the infrastructure and change maintenance practices when LFLRVs are introduced to existing systems. It is suggested that new systems that intend using them should adopt infrastructure standards and practices similar to the type of system for which these types of cars were originally designed. The use of independent rotating wheels on the center trucks, more than any other feature, con- tributes to the performance issues. The research identified the main contributory factors and the guidance makes recommendations to enable the problems to be avoided. In Europe the application of LFLRV designs of different types has been more extensive than in the United States and Canada where only two designs have been applied and those not exten- sively. It may be worthwhile tackling the reasons for this situation. The research has noted the diversity of wheel profiles used on the light rail transit systems of the United States and Canada. The wheel-rail interface is key to solving the problems with LFLRVs and so the report proposes that further work be done to attempt to standardize on pro- files that may have wider benefits.