Traffic noise barrier overlap gap analysis

Abstract

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends was formulated for traffic noise sources. The method accounts for sound propagated from vehicle source positions for a maximum of ten roadway lanes. Six receiver regions were considered based on potential receiver locations with respect to a gap. The analysis identified both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap, which can result in: direct rays, diffracted rays from the top edge of one barrier, diffracted rays from the top edge of both barriers, rays reflected between the barriers, and rays that are both reflected and diffracted. The derived method could be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration (FHWA) for traffic noise propagation are given. Field measurements for up to 30 receiver positions from four overlap gaps were compared with uncalibrated predictions. The equivalent continuous levels, A weighted, were overpredicted by 2–3 dB. When the analysis was based on an octave band characterization of the source, the mean overprediction was reduced to less than 1 dB.