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01 January 2006

Intelligent amber arrows

We have now completed a study aimed at identifying whether intelligent amber arrows would overcome confusion at complex traffic signal junctions, where any combination of left, right and ahead movements may occur at different times within the signal cycle prompting some drivers to start moving when a different traffic stream is signalled.

This project, co-ordinated by John Gilliam of Leicester City Council – in collaboration with the department for transport - was funded by the Highways Agency and by the participating local authorities, including Leicester City Council, Nottingham City Council, Manchester City Council and Bournemouth Borough Council.

Earlier trials with a fixed amber arrow had resulted in an increase of drivers over-running the closing fixed amber/red signal at the end of the green signal sequence. The assumption was made that drivers could not see the fixed amber arrow as clearly as a normal amber roundel, which is what they normally expect at traffic signal junctions. To overcome this problem an intelligent amber arrow has been developed. An intelligent amber arrow opens up as fixed amber arrow, at the start of the signal sequence, and closes as a normal amber roundel at the end of the green phase.

We carried out video surveys at four signal junctions before and after the intelligent amber arrows were installed. The study found no evidence that either fixed or intelligent arrows have a detrimental affect on safety at a junction, but they did show that during the opening amber period amber arrows can overcome the confusion where double headed signals are used to control different movements separately at a stop line. The study also revealed that where speeds are higher, the number of violations during the closing amber period was reduced following the installation of the intelligent amber arrows.

Furthermore, the study suggested that Intelligent Amber Arrows reduce the number of violations during the closing red period at all of the sites. Consequently, there is significant support from practitioners to introduce amber arrows more widely and the Department of Transport has agreed to support the use of intelligent amber arrows at traffic signal junctions within the UK. The DfT has agreed to the use of intelligent amber arrows at a greater number of traffic signal junctions within the UK in order to gain a better understanding of the benefits and develop advice on their use.

This has been a very high profile project for Mott MacDonald further enhancing our reputation in the traffic signal world.
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