A Rating Index for Estimating Insertion Loss of Noise Barriers under Traffic Noise Conditions

Starting from the algorithms based in the geometrical theory of diffraction -GTD- most widely used to predict the Insertion Loss (IL) of an acoustic noise barrier, a simple analytical expression is proposed for the calculation of a descriptor index (expressed in A-weighted dB), which uniquely correlates the protection charateristics of the barrier with the geometrical parameters of the source in relation to the barrier.

From the six implicit parameters involved in the Fresnel number, related to the GTD algorithms, the proposed index is a function only of those corresponding to the source semispace (source height and source-barrier distance).

If an international agreement can be obtained for the source position in respect to the barrier (as occurs with the standardized measuring procedure for the evaluation of the noise emitted by vehicles), the proposed single rating index will only depend on the relative source height. In such a way, the IL characteristics of a barrier expressed in A-weighted dB, can be uniquely obtained through this quantity.

The index proposed in this report, ILA_w gives the protection caused by a screen at far reception distances, expressed in A-weight dB for predetermined emission conditions (traffic noise spectrum, and distances normalized to λ/2). It is shown that ILA_w values can be obtained at distance close to the barrier under predefined error limits, or under the conditon of zero source-barrier distance.