The effect of railway platforms and platform canopies on sound propagation

Abstract

The effect of railway platforms on sound propagation has thus far not been investigated in detail. Due to the vicinity to the track, the platform’s large reflecting horizontal surface, and the often present canopy it is unclear whether standard noise propagation prediction methods can be applied without modifications. Here, the acoustic effect of low railway platforms was investigated using measurements directly at the platform as well as in the distance in order to derive suitable models for the 2.5D boundary element method (BEM) as well as for standardized prediction methods. For the BEM using a source at the center of the track at the height of the platform edge was found to be an optimal solution. Different standard platform variations were investigated. The results show a relatively small, low lying, and localized shielding effect of the platform of up to 3 dB that further diminishes with increasing platform width. In comparison, a low noise barrier at the same position yields up to 4 dB and the effect is less localized. Although a canopy may lead to a better protection of elevated positions, the presence of such a structure also leads to a further decrease of the platform shielding in lower positions. Absorption on the lower side of the canopy can reduce this undesirable effect, however, only when large portions of the canopy are covered with absorbing material. Using the BE calculations and the measurements, two standardized calculation schemes, i.e. the Austrian ONR 305011 and the noise assessment methods defined in the European Directive 2015/996 (EU) were investigated. Both methods overestimate the platform effect. Similar to the BEM, a better agreement is reached when the source position is adjusted to the platform height. Floating elements such as a canopy are not defined in any of these standards, however, non-standard calculations of such objects as already implemented in certain noise mapping software could be used to take into account the attenuation effect for certain receiver positions.