Abstract
A study into the physical properties of noise barriers has been carried out and a single rating index to characterise the acoustical protection of a barrier has been developed, in terms of the barrier diffraction coefficient. An expression for a single figure rating index may be formulated by assessing the insertion loss at a receiver point far enough from the barrier to make the difference between direct and diffracted sound paths from barrier to receiver negligible. This makes the geometry between the barrier and the receiver point redundant in the calculation of insertion loss and thus allows the barrier to be characterised by a single rating index. In this work the insertion loss is expressed as a function of the barrier diffraction coefficient, applying the same geometry conditions. Subsequently an expression for a single rating index is obtained as a function of the barrier diffraction coefficient.