The Forest Service USDA. Research Bulletin
263. โ July 1974. โ 54 p.
Combinations of trees, shrubs, and solid barriers are effective means for shielding sensitive areas from intrusive noise. Reductions of sound levels in the order of 10 to 15 decibels (less than half as loud) are common for 12-foot-high land-forms combined with wide belts of tall trees. Greater reductions have been observed in many instances.
Trees and solid barriers appear to be complementary in reducing noise levels. Either trees or solid barriers may be used separately, but the combination tends to provide more uniform control for a greater distance than does either one alone. Relative placement of the barrier between the noise source and the protected area is of great importance, as is the overall sound propagation distance. Generally, a barrier placed close to a noise source is more effective than one placed midway between source and receiver.
Screening is effective only when the noise source is hidden from view at the protected area, and the effectiveness increases as the height of the screen is increased. Optimum heights are suggested for several applications, and brief instructions for establishing trees and shrubs on land-forms have been included.