Noise barriers are one of the most important measures to reduce the noise burden due to traffic noise. Noise barriers act as an obstacle for the sound propagation and are most efficient in areas where there is no direct line of sight between the noise source and the receiver. The diffraction over the top of the barrier alters the sound field behind the barrier and the effect depends on many factors, e.g. the height of the barrier, the frequency, the distance of source and receiver to the barrier, the height of the source. Unfortunately, with the height of the barrier also the optical barrier effect also increases.
Transparent elements may reduce this optical barrier effect. However, transparent elements are typically sound hard and increase the effect of multiple reflections between train and barrier. This can lead to a reduction of the mitigation effect of the barrier.
Various parameters are relevant for the extent of the reduction in efficiency. Of particular interest are the size and vertical positioning of the reflecting elements. An important question is whether and how such changes can be considered in noise mapping applications.
The project GLAS uses extensive simulations and in-situ measurements to investigate the effect of reflecting elements and to provide a reference calculation model. This can be used as a basis for assessing how well noise mapping approaches such as the ÖAL 28 can approximate the effect of reflecting portions within a noise barrier.
To investigate the effect and options to consider the effect in general state of the art noise calculation procedures, the following steps were defined: