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Effect of Porous Pavement on Wayside Traffic Noise Levels

In 2011, pavement on an eight-lane portion of U.S. Highway 101 in San Rafael and Novato, California, was rehabilitated with the application of an open-graded asphalt concrete (OGAC) overlay as part of a larger project to improve the traffic flow along the 101 corridor. Residents in the area of rehabilitation had periodically complained to the local transportation agency about traffic noise. For an understanding of the noise reduction expected after the application of the new OGAC, wayside traffic noise levels and onboard sound intensity (OBSI) levels were measured at two sites: the site where the new pavement was to be placed and a nearby site that had received new OGAC 1 year earlier. The results indicated that a reduction of 7.8 dB in OBSI tire–pavement noise should be expected, along with a reduction of 7.8 to 8.4 dB in wayside traffic noise. The measurements were repeated after the OGAC application; OBSI reductions of 7.1 dB were found, and reductions of 10.5 and 11.2 dB were found for the wayside levels measured 60 ft from the highway. The comparison of results from previous studies of sound propagation over porous pavements led to the conclusion that this additional reduction in the wayside levels of 3.4 and 4.1 dB compared with the tire–pavement source levels was attributable to the sound absorption provided by the porous pavement.