MOVING THE TARGETS

Most urban area traffic control (ATC) systems, such as those using SCOOT or SCATS, use common, fixed cycle times for their traffic signals. This article describes SPOT, an alternative approach to ATC, which is now running in the Norwegian cities of Oslo, Bergen, and Trondheim, and in 12 other cities in six other countries. In the SPOT system, optimisation of signal settings is based on continuous measurement of real-time data. Each junction is allowed to decide its own signalling strategy for a period of two minutes, though neighbouring junctions have some input. SPOT still aims to improve area-wide traffic flow, but provides for better prioritisation of public transport. It can use tracking information on public vehicles, and give them varying priority according to the urgency of their situation. The ability of each junction to vary its cycle time makes the system seem unpredictable to road users, but 'green waves', adjusted to actual traffic demand, occur if it functions properly. A full evaluation of its effects on traffic behaviour and road safety has not yet been made. The article gives some details of the operation and performance of SPOT in the three Norwegian cities, where test results have shown better traffic flow, shorter journey times for private traffic, and extended priority for public transport.