Briefing: Review of CIRIA Report 142 on highway pollutants

Abstract

Pollutants build up on highways and are washed off during a rainfall event and are usually discharged via an outfall to a watercourse. CIRIA report 142 (1994) guidance indicates that pollutant build-up on highways is a linear process which is proportional to traffic flow and time. This guidance has since been adopted in the Design Manual for Roads and Bridges. However, recent studies suggest that these assumptions may not be ideal. This article explores the pollutant build-up and runoff mechanisms on highways and suggests possible alternative assumptions which may be implemented to enhance the original CIRIA methodology.