The environmental capacity approach to the generation of urban traffic schemes.

This paper describes the environmental capacity approach to the design of urban traffic management schemes. The environmental capacity of a street, or a whole road network, is the traffic volume which is compatible (for a given land use) with specified types and levels of environmental criteria. The approach is illustrated in the form of two case studies, the first for the historic city of Bath, the second a study carried out for a district of London. The paper shows how the design process is necessarily interactive and that the approach can also be of value for the evaluation of alternative schemes. Recent developments in the methodology are described including the use of microcomputer spreadsheets and the addition of an air pollution criterion to the noise, pedestrians environment and visual intrusion criteria contained in the computer package ENV. The paper argues that the approach can aid the development of appropriate hierarchical road networks in urban areas - a facility which is particularly relevant given the increasing interest in route guidance and information technology in such programmes as DRIVE and AUTOGUIDE.