The Educational Railroading Conference Leader Since 1994


2019 Rail Transit Session


Proactive Wheel/Rail Interface Study on a Light Rail System with Independently Rotating Wheels

Shankar Rajaram

Shankar Rajaram
Sound Transit

Modern light rail systems with low floor light rail vehicles (LRV) operated in the United States have a typical design with a three-section articulated car body. The two end cars have powered trucks with solid axles steering the wheels. The center car mounted on an unpowered truck with independent rotating wheels (IRW) connects the two end cars. The IRWs are not self-steering because there is no solid connection between the left and the right wheels in the center truck. Instead, the IRWs rely predominantly on the wheel/rail profile match, including wheel taper, for smooth steering on the tracks. Typically, the wheel life of the center trucks in such LRVs tend to be lower than that of the powered trucks.

This presentation focuses on a wheel rail interaction study initiated on a US light rail system comprising of a 70-percent low-floor vehicle fleet. The vehicles have center cars with independently rotating wheels. The wayside train vibration levels of this system showed an increase at control test sites during a period of 3 years. The increase was mostly limited to frequency bands typically attributed to track resonances. The onboard LRV noise levels in tunnel sections were typically higher than the nominal interior noise limits specified for new light rail vehicles. In addition, the lateral acceleration of the center cars reached noticeable levels at sharp curves. All of the above observations seemed to be related to the wheel rail interface. As a result, a wheel/rail interaction study was initiated with the goal of maintaining wayside noise and vibration levels, improving onboard noise and ride quality, and enhancing the life of track and rolling stock components.

As part of the wheel rail study, a representative population of rail cross-sections and wheel profiles were baselined. The wheel profiles indicated that the wheel wear pattern of the center cars with independent rotating wheels was different from the wheels on the power trucks. The onboard measurements showed that the center truck lateral acceleration is higher at the curves. The rail grinding program was designed to correct the rail profiles and achieve a smooth surface finish. Other tasks in progress include modeling of the vehicle dynamic behavior to understand the wheel rail interactions. There are also considerations to study the behavior of center cars with friction modifier systems.

This presentation will discuss how the wheel rail study is managed and provide a status of the study including preliminary results. The effectiveness of recent rail grinding from a vehicle performance perspective will be shown using wayside and onboard noise and vibration data. The presentation will also include other relevant results and the anticipated next steps in this study.