The chapter discusses the basic principles of traffic signal control and elementary theory for a street network, and especially for a series of signal-controlled junctions along a main road. Through suitable coordination of the signal settings at successive junctions, it is often possible to establish a green wave, whereby a platoon of traffic may pass through a sequence of junctions without stopping. A time-distance diagram provides a good way to represent the off-line coordination and control of traffic signals along a road. There are two basic approaches to the difficult problem of obtaining good coordination of green times along a road in both directions. The proactive approach identifies paths to which traffic should be attracted, and coordinates settings to reduce travel times on these paths. The reactive approach gives priority to no path, but attempts to optimise a performance index, such as a weighted combination of delays and stops. A platoon dispersion formula and a cyclic flow profile traffic model are presented, which form the basis for the SATURN traffic simulation model, the TRANSYT off-line traffic signal optimisation tool, and the SCOOT on-line traffic control system, where traffic signal settings may respond to varying traffic flows. The TRANSYT and SCOOT systems are described briefly. For the covering abstract, see IRRD 892228.
Abstract