Field investigation of the effects of vegetation on the performance of roadside noise barriers

The effects of nearby foliage on the performance of noise barriers are not well established. Foliage may decrease noise levels behind a barrier, either by back-scattering or absorbing sound. Foliage may also increase noise levels by scattering sound which would normally pass above the barrier into the shadow zone. Field test sites were identified to study these effects. Traffic noise levels were measured simultaneously behind foliage and no-foliage configurations and the results compared. Both increased and decreased noise levels behind the barrier were seen, with most effects being less than 5 dB.