In the design of noise mitigation for rail transit often every decibel of noise reduction is needed to eliminate noise impacts to adjacent communities. In certain circumstances, track design incorporates concrete slab track instead of ballasted track. Track ballast is an effective sound absorber of wheel/rail noise, whereas a concrete slab is highly reflective resulting in greater levels of wayside noise. Wayside noise barriers alone may not provide enough noise reduction benefit requiring additional noise control at the source. In certain cases, trackbed absorption that has been used in Europe may be an option to consider. In this paper we explore the use of porous concrete sound absorptive panels applied on the concrete slab trackbed to reduce wayside noise from rail transit operations on slab track. We provide an overview of the application and use on German railway systems. We examine the potential noise reduction effectiveness relative to the noise reduction provided by ballast and tie track. We discuss potential benefits and limitations for use on transit projects in the United States with attention to practical issues such as installation, maintenance, drainage, and service life.
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