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System Requirements

  • SCOOT is an on-line UTC (urban traffic control) system.

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Split Cycle and Offset Optimisation Technique

World famous adaptive urban traffic signal control system

In urban areas where traffic signals are close together, the co-ordination of adjacent signals is important and gives great benefits to road users. Co-ordinating signals over a network of conflicting routes is much more difficult than co-ordinating along a route.

Early work developed off-line software to calculate optimum signal settings for a signal network. TRANSYT, developed by TRL, is probably the best known example. TRANSYT can be used to compile a series of fixed time signal plans for different times of day or for special recurring traffic conditions.

Preparing such signal plans requires traffic data to be collected and analysed for each situation and time of day for which a plan is required. This is time consuming and expensive and unless plans are updated regularly as traffic patterns change they become less and less efficient. To overcome these problems, the concept of a demand responsive UTC system was developed. Initial efforts were not successful, mainly because of a continuing reliance on plans, either pre-prepared or dynamically developed.

TRL developed a methodology to overcome these problems. An on line computer continuously monitored traffic flows over the whole network, fed the flows into an on-line model, similar to that used in TRANSYT, and used the output from the model as input to its signal timing optimisers. These optimisers made a series of frequent small adjustments to signal timings to minimise the modelled vehicle delays throughout the network. This was the basis of SCOOT, which, has been continuously developed to meet the needs of today's traffic managers.

SCOOT has proved to be an effective and efficient tool for managing traffic on signalised road networks and is now used in over 250 towns and cities in the UK and overseas. SCOOT uses data from vehicle detectors and optimises traffic signal settings to reduce vehicle delays and stops. There are a number of basic philosophies which led to the development of SCOOT. One of these was to provide a fast response to changes in traffic conditions to enable SCOOT to respond to variations in traffic demand on a cycle-by-cycle basis. SCOOT responds rapidly to changes in traffic, but not so rapidly that it is unstable; it avoids large fluctuations in control behaviour as a result of temporary changes in traffic patterns.