Sensitivity of predicted barrier attenuations to errors in specifying ground plane geometry

Abstract

When the ground behind a noise barrier may be regarded as acoustically locally reacting, and where it has reasonably level topography, there is a plausible rationale for a traffic noise prediction model based on barrier diffraction of geometric image terms with coherent summation. Often in real life, however, even when sideline terrain surface is essentially plane, its plane is neither coplanar with the highway pavement nor even parallel to it. Defining the ground “plane” from measurements on the site, moreover, is not a task likely to be done with great precision in normal noise assessment practice. The sensitivity of traffic noise level predictions to errors in ground‐plane location then becomes of interest. In this connection a study has been made of a series of ground‐plane configurations approximating to cases arising in practice. Each case has been perturbed systematically, and the resulting differences in predicted noise levels have been observed. It has been particularly of interest to note the decrease in sensitivities resulting from averaging over frequency and over a traffic line. [Work supported by FHWA.]