Application of absorption data from SOPRA sound reflection index measurements in Nord2000 road noise calculations – results from a case study

Paper in proceeding, 2026

Sound absorption data, obtained by in-situ sound reflection measurements on noise barriers and other surfaces in infrastructure, have been applied in traffic noise calculations with the Nord2000 model in SoundPLAN. The purpose was to study if different absorption values from real examples resulted in different calculated levels of noise reduction and changes of the frequency spectra in realistic situations. Most of the data describing the acoustic performance of the absorbers originate from the quick reflection index, RIQ, from previous measurements with the SOPRA method, which is a simplified version of the European standard method EN 1793-5 for measuring the sound reflection index (RI) of road noise barriers in direct sound field, i.e., in-situ. Several types of noise barriers, constructions and actual absorber materials have been measured, either with the SOPRA method or by the manufacturer according to the standard EN 1793-5. The active sound absorbing parts were mineral wool, LDPE (low-density polyethylene) foam, porous concrete and cement-bound wood wool. This paper presents the results from a case study where the absorption data, in one-third octave band values, were applied on noise barriers in SoundPLAN models of real sites for road noise calculations. The existing noise barriers in the locations are made of sound reflecting materials like concrete and polycarbonate. Three alternative absorber applications were studied: on the roadside, on the receiver side and on both sides of the noise barriers. The tested absorber types were applied to all the alternatives. Since the number of measured samples of each absorber type is quite small, general conclusions about the sound absorbing performance of the materials cannot be drawn. However, it can be concluded that the absorbers reduce the noise levels and that the different absorber types of the study result in different noise level reductions, both in single-number values and in spectra.