A traffic signal system for high-speed roads : TARU 3/71

This report describes the development of a traffic signal system for use on high speed roads. The aim of the system is to reduce the risk of driver error by minimising the chance of the traffic signals changing from green to amber while a vehicle is within the dilemma zone associated with its approach speed. The equipment developed consists of a series of conventional vehicle loop-detectors installed in the roadway on the high speed approach to the signals. These detectors are coupled to a standard traffic signal controller through a timing and detector output control device which renders the detectors sensitive to vehicles in certain speed ranges. The relationship between the distance of each detector from the stop line and the range of its speed sensitivity are derived from Crawford’s experimental results on driver judgement and error during the amber period at the traffic lights.