Influence of barrier tops on noise levels: new BEM calculations

The Danish Road Directorate is currently investigating the possibility to optimise noise barriers by using specially shaped tops. The noise level at different positions behind the noise barrier has been calculated using the boundary element method with the help of the OpenBEM software. The simulated situation is a barrier between a residential area and a motorway. The highway is modelled as a two-lane road and the sound levels are predicted at 10 m, 20 m and 40 m behind the barrier, respectively. Seven different types of barriers were tested including L-, T- and Y-tops as well as more a complex geometry such as a threepanel top. The results show that the T-shaped barrier offers most noise reduction compared to the others. It can indeed bring up to 6.6 dB extra noise reduction at a position 40 m behind the barrier compared to a regular barrier. This study also shows that the noise attenuation achieved with the different tops is dependent on the receiver position. Following this study, in-situ measurements will be carried out in an attempt to validate the predicted noise levels.