Noise barriers such as walls, fences or earth mounds are often used to reduce traffic noise pollution. An alternative, which is likely to be environmentally and aesthetically more pleasing, is a belt of vegetation. This report describes a literature survey to investigate the effectiveness of vegetation in reducing traffic noise annoyance, and a field study which measured traffic noise attenuation through five vegetation types up to a depth of 30 m. Both the literature and the field study found that foliage is important in reducing high frequencies (above 2000 Hz), while low frequencies (250 to 500 Hz) are attenuated by the absorbing qualities of the ground - qualities which may be enhanced by the plant root system and leaf litter. The maximum attenuation in the field study was measured through 30 m of dense spruce plantation. This gave a noise reduction 6 dB(A)L10 greater than the same depth of grassland. However, the effectiveness of the vegetation was greatest close to the road, and 10 m of vegetation gave a noise reduction 5 dB(A)L10 greater than grass, or 8 dB(A)L10 greater than the theoretical attenuation over a hard reflecting surface. Narrow belts of vegetation may therefore be worth considering for noise reduction purposes. (A)

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