Guidelines for optimizing road traffic noise shielding by non-deep tree belts

This paper discusses that a non-deep tree belt along a road can be an interesting solution to achieve road traffic noise reduction. Noise shielding is mainly obtained as a combination of multiple scattering in the tree trunk layer and due to the presence of an acoustically soft soil. A large dataset of full-wave and highly detailed numerical simulations, based as much as possible on measured input data, shows that high biomass density should be strived for as a general rule. This conflicts, however, with practical limitations regarding access to light, nutrients and water for the trees. Some interesting approaches have been identified to relax the need for high biomass density, without affecting noise shielding to an important extent. Rectangular planting schemes, where the spacing orthogonal to the road can be increased, omitting full rows parallel to the road length axis, and thinning inside the belt are examples of such measures. It is discussed that the specific choice of a planting scheme could make a tree belt along a road an efficient noise reducing measure or not.