The effects of traffic management and control on vehicle capacity in London

Journey speed is a good measure of the performance of a road system in a town, provided it allows journeys to be made by a reasonably direct route. Journey speed and its changes have also been used as a measure of performance of the effect of traffic management schemes. The standard method of measurement, a moving observer car technique, was used extensively in the measurement of the effects of urban traffic control techniques (UTC). It has been shown that journey time reductions of at least 12% could be achieved by UTC. However, introducing UTC and other traffic management techniques in London, has not increased the average journey speed as measured by the regular surveys. There is clearly a finite limit to the capacity of a road network during which traffic moves at an acceptable speed. Attempts have been made to predict this and a method by Wardrop (1976) is described. This shows that the traffic capacity of the network has increased over the years but recent data suggests that it has probably reached a maximum. The author considers whether the application of further traffic management techniques such as SCOOT and Autoguide will achieve the actual improvements that are predicted by theoretical techniques