A RATING INDEX FOR ESTIMATING INSERTION LOSS OF NOISE BARRIERS UNDER TRAFFIC NOISE CONDITIONS

Starting from the algorithms based in the geometrical theory of diffra ction -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), w hich uniquely correlates the protection characteristics of the barrier with the geometrical parameters of the source in relation to the barr ier. From the six implicit parameters involved in the Fresnel number, related to the GTD algorithms, the proposed index is a function only o f those corresponding to the sources semispace (source height and sour ce-barrier distance). If an international agreement can be obtained fo r the source position in respect to the barrier (as occurs with the st andardized measuring procedure for the evaluation of the noise emitted by vehicles), the proposed single rating index will only depend on th e relative source height. In such a way, the IL characteristics of a b arrier expressed in A-weighted dB, can be uniquely obtained through th is quantity. The index proposed in this report, ILA(omega), gives the protection caused by a screen at far reception distances, expressed in A-weight dB for predetermined emission conditions (traffic noise spec trum, and distances normalized to lambda/(2)). It is shown that ILA(om ega), values can be obtained at distance close to the barrier under pr edefined error limits, or under the condition of zero source-barrier d istance.