This paper describes the mechanisms governing the generation and propagation of noise from road vehicles running on porous road surfaces and reviews the considerations given to obtain design guidelines for feasible low noise porous road surfaces for high speed road applications. It is concluded that a 20mm maximum aggregate size porous road surface laid to a thickness of 0.05m, and with an optimised binder content to maximise the total void volume in the layer, will provide substantially lower noise levels from road vehicles than equivalent non-porous Hot Rolled Asphalt (HRA) surfaces. In addition, the surface design will provide distinct advantages in terms of spray suppression and resistance to clogging when compared with other designs of porous road surfacing made with smaller aggregates. In practice, roads surfaced with 20mm porous asphalt (PA) have been found to lower vehicle noise levels by 5 - 6 db(A) compared with the noise generated on an equivalent non-porous road surface. (A)
Abstract