Road Surfaces (Hansard, 2 December 1996)

§ Mr. Watts

I have asked the chief executive of the Highways Agency to write to the hon. Member.

Letter from Lawrie Haynes to Mr. David Chidgey, dated 2 December 1996: The Secretary of State for Transport has asked me to reply to your recent question asking what are the (a) construction, (b) cost and (c) environmental criteria which determine where and when low noise, open textured, road surfacing should be used on trunk roads or motorways instead of, or as a replacement for, concrete or standard bituminous construction. Low noise surfaces may be considered for new roads, or those which are being substantially altered, where these pass through noise sensitive areas. Their environmental benefits are considered during the development of the detailed design of a new road scheme and balanced against the additional costs of their use compared with 477W alternative means of reducing the impact of traffic noise. The need to replace the surface of an existing road is determined solely by criteria relating to its residual life and skidding resistance. Porous asphalt is the best known of low noise, open textured, surfacing. It has been subjected to extensive trials and we have established technical criteria for ensuring acceptable durability. Guidance on the criteria for construction is provided in the HMSO publication The Design Manual for Roads and Bridges, Volume 7: Pavement Design and Maintenance. The guidance includes advisory limits on traffic intensity and other factors affecting the practicality of its use. It is not Highways Agency policy to use porous asphalt as an overlay for existing roads partly because the surface drainage arrangements need to be altered, but also because the substantial additional costs cannot be accepted without any offsetting saving on other necessary noise mitigation measures or financial compensation. Other types of open textured surfacing are being developed such as thin bituminous overlays. Examples have been approved for limited use in trunk road and motorway maintenance to restore skidding resistance. These products appear to offer promise through reduced noise levels when compared with conventional road surfaces, but have not yet demonstrated their ability to withstand heavy traffic. It is too soon to say whether or not these products will provide an economical alternative to conventional bituminous asphalt overlays. There are particular difficulties with thin overlays on jointed concrete roads because of the tendency for the joints to be reflected as cracks in the surface material, causing a line of weakness. The trials with the new thin surfacing products include techniques to address this problem and are being monitored as part of the Highways Agency's continuing programme of research and development.