Programs for traffic signal design

Abstract

A number of computer programs have become available in recent years as an aid to the design of signal-controlled junctions. These can be used to help determine the optimum geometric design of the junction, calculate appropriate signal settings for control purposes and predict queues and delays at the junction. Such programs are widely used and are a valuable aid to the traffic engineer, but do not remove the need for experienced design engineers. For example, the choice of stage sequencing, phase combinations, geometric details and so on still require the skill of the designer; the signal programs then provide a powerful tool for evaluating different alternatives and for optimisation. Other issues outside the scope of signal programs, but vital in the design process, include:

• (1) ‘designing for safety’ (for example, correct intergreen/minimum green settings and minimisation of conflicts);

• (2) adequate provision for all road users, including heavy vehicles (for example minimum turning circles), buses (for example, bus stops, priority facilities) and cyclists/pedestrians (for example, special protection/signalling facilities);

• (3) other design issues, such as junction location, signing, lighting and environmental impact.