Effect of Plantings on Radiation of Highway Noise

Abstract

The body of information presented in this paper is directed to those individuals concerned with the location of highways relative to either existing or planned residential communities. The paper treats in depth the expected attenuation of automobile and particularly diesel tractor-trailer generated hoise by the interposition of extensive and dense planting of trees and shrubs between the highway and the community. The results of research, by the author and others cited in the paper, gives clear indication that a belt of dense man-made growth of tall trees and underbrush can give as much as 5 to 8 dB truck/car noise reduction per 100 ft of planting depth. Natural growth of deep forests were measured to give from 3 to 5 dB attenuation per 100 ft of planting depth. Planting depth of at least 100 ft is required to give reliable results, with tree heights of 40-50 ft desirable and densities of 50-70 ft visibility needed for good effect. The paper provides considerable experimental verification by an analysis of the current literature. The types of noise sources in cars and trucks are briefly treated as are community reactions to noise from such sources. The dBA is used as the accepted measure for characterizing truck and automobile noise. Both spherical and cylindrical radiation of sound are discussed for low density and high density traffic, respectively. The paper concludes with an example of attenuation of a typical truck noise by spherical and cylindrical radiation for low- and high-density traffic and a 200-ft deep planting of dense, mature forest. It is concluded that a mature belt of either coniferous or deciduous forest with underbrush can produce barely acceptable noise levels in the community which is separated by such a noise barrier from a heavily traveled highway.