Since 1989 an Automatic Incident Detection (AID) system has been in operation on an 83km section of the English M1 motorway. The system was designed by the Highways Agency to automatically detect and locate slow moving or stationary traffic on the northbound and southbound carriageways. Warning signs, in the form of an advisory 50mph speed limit, can then be set upstream of the queues to advise drivers to reduce speed. Once normal flows are re-established the system automatically turns off the warning signs. When the AID system was installed it was expected that there would be benefits in terms of a reduction in the numbers and severities of accidents into the backs of queues of traffic. Also, because of the automatic nature of the system, more timely setting and removal of warning signs were expected to minimise flow disruption and reduce delays to journeys. Additionally, the system was also expected to benefit the emergency services, as the motorway control centres should be able to accurately locate incidents and route emergency services to the scene. This report details the results of a before and after study of the benefits of installing the AID system on the M1 motorway. Each of the potential benefits of the AID system are presented together with an overall figure for the cost saving per year following the installation of the system. (A)

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