Urban cities and road traffic noise: Reduction through vegetation

This study was carried out to determine the effect of roadside vegetation on the reduction of road traffic noise under varying planting intensities. Roadside vegetation ranging from minimal planting through to moderate and dense plantings were used. The results showed that the traffic noise was reduced by 50% when vegetation was enhanced from a minimal to moderate planting intensity, and no enhancement in noise reduction was observed as vegetation was further increased to a dense intensity. A 5 m depth of vegetation barrier was found to be an ideal depth for traffic noise reduction. Without the vegetative barrier, the observed mean noise levels were 78 dB. On average, vegetative barriers (moderate to dense) were able to reduce traffic noise by 9–11 dB. Trunk size was found to be linearly related to traffic noise abatement and synthetic barriers were found to be inferior to tree belts both psychologically and in absolute values of noise. This report also investigated the effectiveness associated with setbacks where it was found that the greater the setback distance, the higher the level of noise amelioration and a 10 m depth was identified as the threshold for an effective tree belt.