Guidance for noise reduction provided by tree belts

The effects of noise reduction of six tree belts were examined. An amplifier was placed in front of each tree belt, while a noise meter was placed at various heights and distances behind the tree belt. Net noise reduction effect termed as “relative attenuation” was obtained by subtracting the sound pressure level at each measurement site behind the tree belt from the sound pressure level at equal distances over open ground. Five parameters, including visibility, height, and width of the tree belt, height of receiver and noise source, and the distance between noise source and receiver, were studied. A multiple regression model demonstrating the order of importance of the five parameters in relation to relative attenuation was developed. The five parameters were then transformed into three-dimensionless parameters, i.e., h′: receiver and noise source height/tree height, d′: distance between noise source and receiver/tree height, and m′: belt width/visibility. By plotting the relative attenuation on the coordinate axis of h′, d′ and m′ and curve fitting, a three-dimensionless map of noise reduction by tree belts was formed. The map can be used as guidance in designing three belts for noise reduction in environmental planning.