Urban Transport Strategy. Management in Developing Countries John A Cracknell, страница 104

Traffic Signals and “Area Traffic Control”

Rationale and Objectives.  The objectives of traffic signals are:

§  To control traffic movements at conflict points (usually junctions but also at pedestrian crossings or vehicle merges) in order to maximise road capacity and to ensure safe operation

§  To assist realise traffic management strategy by giving priority to buses, by assisting pedestrians and cyclists, by regulating traffic demand through managing traffic queuing.

Traffic signals can be linked together to co-ordinate the operation of signals over a route, a corridor or an area.  In developed cities, area wide co-ordination has been proved to provide significant benefits in terms of journey times, number of times traffic stops and so on.  Where co-ordination is under the control of a central computer, the system has been termed “Area Traffic Control or ATC” (in some countries “Urban Traffic Control” or UTC is used as the system can be used to control more than junctions such as variable message signs for car parks or directions, congestion monitoring and other management facilities).  There is an increasing trend towards systems which respond dynamically to traffic flows.

Types of Intervention – three general categories of traffic signal schemes exist.

§  Traffic signals at isolated junctions or sites (such as pedestrian crossings) to resolve an accident or capacity-conflict problem;

§  Linked traffic signals at a number of junctions usulally along a corridor using non-computer methods such fixed cable or cable-less linking.  The latter operate by synchronising each signal through the use of the regular pulses from the electricity supply with a battery back-up in case or power failure. Linking schemes can be used for small groups of signals in locations where central computer control is not justified;

§  Area wide systems (ATC) to control and co-ordinate all signals and to provide the ability to implement various management strategies such as public transport priority, emergency routes, queue management etc.  The following ATC systems exist: