A pilot `controlled motorway' has operated on the south west quadrant of the M25 motorway around London since August 1995. The pilot's concept is to deal with or prevent traffic flow breakdown by controlling traffic speeds at times of heavy flow. This could result in reduced accidents, more driver comfort, and perhaps an increase in throughput over the controlled section. This paper describes the monitoring and assessment of the scheme, which was conducted by the Highways Agency and its contractors; it summarises the results obtained during the first two years of operation. For drivers, the most obvious feature of the controlled motorway is the new generation of mandatory motorway signals, which have replaced the traditional advisory signals mounted on gantries over the lanes. The new signal is the CMI (Controlled Motorway Indicator), which can display speed limits from 20mph to 60mph, and `lane closed', diversion, and fog warnings. The speeds displayed to drivers are controlled automatically by MIDAS systems. Detailed assessments were made of every aspect of the pilot scheme, including comprehensive technical and operational assessments of the signals, the enforcement system, and MIDAS. The Transport Research Laboratory (TRL) monitored the scheme's effectiveness in influencing traffic and driver behaviour.
Samenvatting