A model to calculate traffic noise levels from complex highway cross-sections

A semi-empirical model is described which predicts traffic noise levels near roads with adjoining structures which give rise to both screening and reflection of traffic noise such as retained cuttings, multiple barrier configurations and structures which involve a combination of these features. In particular, the model provides a means of examining the insertion loss performance of different designs and the benefits of acoustical absorbent materials placed on the faces of barriers and walls. The modelling philosophy adopted covers the location and directivity of the source, scattering by reflecting elements and attenuation with distance over different surfaces. The techniques of ray acoustics and image source modelling have been employed to account for both single and multiple reflections of noise, absorption by surfaces and diffraction by the edges of barriers and screening walls. The results of a validation study, where model predictions were compared with both real site and scale model measurement, showed that the model gave accurate predictions for a broad range of propagation conditions. Included in the Report are illustrations of the use of the model to examine the noise benefits to be derived from fitting absorbent material to barriers and the walls of cuttings.