Light Rail Vehicle Noise: Evaluation of Rail Roughness and Noise from Wheel Rail Interface
Sound Transit opened its first light rail line, the Central Link, in Seattle, Washington, in 2009. There were many community noise issues immediately after the line went into revenue service that were generally attributed to poor quality rail grinding when the initial mill scale grinding was performed. As a result of that experience, Sound Transit has been cautious when predicting noise and designing noise mitigation for new alignments. Future alignments include the University, Northgate, and Lynnwood Links to the north; the Federal Way and South 200th Links to the south; and the East Link to the east. Over the next 15 years, the system will be expanded from 16 mi to more than 50 mi. The detailed noise data collected as part of the final design of East Link suggest that measures could be taken to reduce the need for substantial noise mitigation on future Sound Transit extensions. This paper summarizes the measurements and key observations from that noise study. One key observation suggests that through implementing acoustic rail grinding and maintaining the current wheel truing program, there is potential for minimizing the amount of sound walls required to achieve community noise goals. The results also suggest that through a detailed, information based investigation, reference noise levels used to determine the need for noise mitigation could be reduced by approximately 4 dB. However, the results of this study, combined with experience from rail roughness studies in general, suggest that achieving a true acoustic rail grinding that leaves no artifacts is not straightforward, because it requires careful monitoring by the rail grinder operator as well as quality control measurements by the grinding company or the transit system.