Detailed full-wave numerical calculations, partly based on measured input data, show that tree belts can be much more efficient than commonly thought. For road traffic noise applications, the trunks and the forest floor are expected to be responsible for the main part of the noise shielding. The choice of planting scheme and tree belt depth are essential parameters at realistic tree densities. The noise attenuation provided by a tree belt is discussed in relation to the one obtained by traditional thin rigid noise walls. The reference ground type between the edge of the road and the receiver showed to be an important parameter in this comparison. In case of rigid soil, a 30-m deep optimized tree belt could give a similar A-weighted sound pressure level as a 4-m high noise wall at receiver distances exceeding 50 m. For grass-covered ground, the equivalent noise screen height is typically lowered with roughly 1 m. Although both types of noise abatement change the frequency balance in a different way, the course of A-weighted sound pressure levels versus Zwicker loudness is rather similar.
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