A parametric investigation of the performance of T-profiled highway noise barriers and the identification of a potential predictive approach

Although a considerable amount of research has been undertaken regarding the performance of T-profile noise barriers, the information available to the practicing highway engineer is confusing. For example, there is a widespread belief that the performance of a top edge, expressed as an insertion loss relative to that of the simple barrier on which it is mounted, is constant, irrespective of the relative locations of the source, barrier and receiver. In order to clarify the situation an investigation has been undertaken, using computer modelling, of the performance afforded by highway noise barriers with T-profile tops with different acoustic treatments. The relative insertion loss was found to increase systematically with increasing top width. Although the relative insertion loss afforded by a reflective T-top is small, significant attenuation can be obtained with an absorptive top. Examination of the effect on performance of the locations of source and receiver relative to that of the noise barrier indicated that, for source and receiver locations typical of those experienced for highway noise barriers, the relative insertion loss for a given width of T-top was a function of (a) the path difference between sound travelling to the receiver via the barrier top and direct sound from the source to the receiver and (b) the barrier height. Plots of relative insertion loss versus the path difference, normalised with respect to barrier heights, for a range of T-top widths and absorbent treatment, resulted in a collapse of data around well defined trend lines which offer the potential of being developed into a prediction method.