Esso Energy Award Lecture, 1982: Coordinating Traffic Signals to Reduce Fuel Consumption

Congestion at traffic signals in Britain wastes between 500 and 1000 Ml of fuel every year; at least one half of this waste occurs in central urban areas. The waste can be reduced by coordinating the timings of adjacent signals but it is difficult to achieve good coordination because traffic flow patterns are complex and the effects of signal timing changes are widespread. To help solve this problem, the Transport and Road Research Laboratory has developed a computer program, called TRANSYT, that models traffic movements and optimises the signal timings to minimise delay and stops. This paper describes the principles of TRANSYT and how the method has been extended and used to predict and minimise vehicular fuel consumption in urban areas. Transyt calculates fixed time coordination plans that are optimised for average flow patterns, e.g. during a typical evening peak period. A new method, called SCOOT, continuously measures flows and congestion, predicts current queues and automatically adjusts the signal coordination as the traffic patterns vary. An outline is given of the principles of SCOOT and its potential uses as part of a driver information system.