Diffractors on a low screen: a valid alternative for conventional noise screens along multi lane motorways?

Abstract

Diffractors are an innovative way of shielding noise from e.g. motorways by bending the propagation direction of sound waves upwards and hence creating an acoustic shadow area along the road. The bending upwards is done by the interaction of the road noise with a series of slits, all parallel to the road but with varying depths for varying resonance frequencies. This principle has been invented about 10 years ago and has since then been tested with temporary and permanent constructions. The slits can be integrated in the ground, but can also be put on a low (0,5 - 1 m) screen for enhancing the performance at short distance. The Belgian Road Research Centre has carried out several measurement campaigns at different diffractor set ups on low screens. The measurements were of the "Controlled Pass-By" type yielding consistent results. An overview is given of the findings since the first measurement, including the new results obtained along a ring road in the Dutch town of Amersfoort in 2022, where for the first time such a device was constructed along a 2 x 2 lane, showing the performance in case the noise source is at a larger distance from the diffractor.