The effect of ground cover on truck pass‐by A‐weighted sound level measurements

Abstract

To determine the effect of different ground covers on sound‐level readings, A‐weighted sound levels [dB(A)] from more than 1000 trucks were measured with 16 pairs of microphones. For each pair, one microphone was located on a “hard” site and the other on a “soft” site (a soft site occurs when grass cover is (12) or more of the distance between the microphone and the center of the lane of travel). The microphones were used at three locations simulating typical enforcement of vehicle noise regulations and varied from 41.5 to 71 ft from the center of the lane. As a truck passed each pair of microphones, the maximum dB(A) was recorded and the difference determined. Results indicate that as the amount of grass cover increases, the dB(A) difference between a hard and soft site increases; however, the average dB(A) difference for hard and soft sites is less than the correction factor used for enforcement of the Interstate Motor Carrier Noise Emission Standards.