Abstract
A model is proposed for city centre traffic in which vehicles occupy discrete cells on a closed circuit, and are delayed by blockages which occur independently and at random. The blockages represent the effects of pedestrian activity and turning, parking and crossing traffic. Steady-state relationships between speed, flow and concentration are derived which fit existing Central London data quite well. The model is also used to illustrate some of the problems involved in trying to estimate such relationships from samples, and some qualitative conclusions are drawn about the stability of congested urban traffic flow.