Since 1977 Slough Borouch Council have operated a compact urban traffic control (UTC) system in which a central computer coordinates the timings of traffic signals in slough. The signals are controlled by a flexible progressive system in which the central computer allows the timings to vary by a few seconds from the preset 'fixed time plans' which maintain coordination. The variations in timings are determined by the presence or absence of vehicles over stop-line detector loops; similar systems have been used for many years at other sites. In spring 1983, the TRRL conducted a survey to compare the flexible progressive system with a fixed time system that used the same coordination plans. A 'floating car' survey method was used to measure journey times along the A4 bath road and A355 Farnham road during four periods of the day for five weeks in spring 1983. The results show no significant differences in journey times measured with the two control systems, although there is some indication that the flexible progressive system gives slightly shorter journey times in the morning peak. It is possible that the flexible progressive control system can adapt to small changes in flow, and so reduce the need for updating the fixed time plans. (Author/publisher)
Abstract