Review of traffic signals on high-speed roads
In the UK, dilemma zone protection traffic signal control strategies are required on approaches where the 85th percentile speed exceeds 35 mph (where 15% of free-flow approach speeds exceed 35 mph (56 km/h)). The UK Department for Transport commissioned TRL to reassess the size and position of the dilemma zone, the speed at which traffic signal approaches should be classified as 'high-speed', and to review policy and practice used abroad. The 'Webster and Ellson' test track trials showed that at traffic signals acceptable stopping distances for the majority of drivers (90%) were foundto approximately equate to a one second brake reaction time and an average deceleration of 3.6 m/s². The video studies in this project showed that most drivers were not prepared to use decelerations as high as shown by Webster and Ellson, and drivers stop-continue decisions were found to be largely based upon their journey time to the stopline at the onset of amber, not upon braking ability. The results aligned with the 'Zeeger' on-street findings. The propensity to red-run was found to be very high, with 90% ofdrivers continuing if 2.5 seconds from the stopline and 10% continuing if4.5 seconds from the stopline (for all speeds between 35 mph and 55 mph (89 km/h)) - in the UK the stopping amber is three seconds. In-service Large Goods Vehicle (LGV) braking performance is much lower than cars, with some unable to achieve the stopping distances derived by Webster and Ellson.LGVs were found to be about one-and-a-half times more likely to run-the-red than other vehicle types, and run-the-red later. Dilemma zone events account for a notable proportion of red-light violations at higher speed sites, and appear to account for a significant proportion of rear-end shunts.The main policy in the UK for traffic signals on high-speed roads has been to limit the number of dilemma zone events through specific traffic control strategies. Recent developments in traffic control include 'optimisation' strategies, which allow green to end when there are no closely following vehicles in the dilemma zone, i.e. negating the chance of a rear-end collision, but not red-running; and specifically providing extensions for large vehicles. Alternative methods to address the dilemma zone issue include: speed reduction; longer amber periods; advanced warning of the amber period; and red-light running cameras. The effectiveness of each of these strategies is reviewed, and an assessment made as to their applicability. For the covering abstract see ITRD E135582.
- Record URL:
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Availability:
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Corporate Authors:
Association for European Transport (AET)
1 Vernon Mews, Vernon Street, West Kensington
London W14 0RL, -
Authors:
- MAXWELL, A
- WOOD, K
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Conference:
- European Transport Conference (ETC)
- Location: Strasbourg , France
- Date: 2006-9-0 to 2006-9-0
- Publication Date: 2006
Language
- English
Subject/Index Terms
- TRT Terms: Automobiles; Behavior; Conferences; Crimes; Decision making; Drivers; Rear end crashes; Red interval (Traffic signal cycle); Traffic signals; Trucks; Yellow interval (Traffic signal cycle)
- Uncontrolled Terms: Trlart
- Geographic Terms: United Kingdom
- ITRD Terms: 559: Amber light; 9001: Behaviour; 1243: Car; 8525: Conference; 2248: Decision process; 1772: Driver; 1236: Lorry; 1516: Offence; 1620: Rear end collision; 539: Red light; 565: Traffic signal; 8119: United Kingdom
- Subject Areas: Motor Carriers; Operations and Traffic Management; Security and Emergencies; I73: Traffic Control;
Filing Info
- Accession Number: 01089894
- Record Type: Publication
- Source Agency: Transport Research Laboratory
- ISBN: 1905701012
- Files: ITRD
- Created Date: Mar 17 2008 10:11AM