THE DEVELOPMENT OF SCOOT
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.
New features have been added as SCOOT has been developed. Traffic management features have been added and refined in each version. Major enhancements include:
- Version 3.1 included bus priority, database facilities and incident detection.
- Version 4.2 added estimates of the emission of pollutants.
- Version 4.5 enabled the bus priority to differentiate between different buses, e.g. to give more priority to late buses, enhanced the technique to "gate" traffic into sensitive areas and provided extra help to engineers setting up a system.
- SCOOT MC3 has enabled the Kernel software to safely use data supplied by packet switched communications systems, provided a congestion supervisor and increased the priority available to buses by allowing stage skipping where it is appropriate.
- SCOOT MC3 Service Pack 1 introduced strategies which gave controllable priority to pedestrians at stand alone pedestrian crossings so as to reduce their waiting times.
- SCOOT MMX provided additional facilities to prioritise pedestrians at junctions, a significant update and enhancement of emissions estimates as well as features to improve operation during low flow periods.
- SCOOT MMX Service Pack 1 provided a facility Journey Time Reliability (JTR) to help engineers to control the SCOOT link saturation level more effectively and thus assist them in improving the Journey Time Reliability along key routes.