Highways Agency

Controlled Motorways

Aim

To improve traffic flow, improve journey times and cut accidents by delaying or preventing the start of stop-start conditions familiar to many drivers. This smoother traffic flow is achieved by automatically reducing speeds at peak times in response to traffic speed and flow.

What it means for motorists

• Less congestion and improved traffic flows
• More reliable, smoother journeys
• Less aggressive driving such as tailgating
• Better use of lanes and less lane changing
• Reduction in accidents
• Increased throughput of vehicles
• Environmental improvements i.e. reduced traffic noise, vehicle emissions and fuel consumption

Main features

• The system uses mandatory speed limit signals, displayed on overhead gantries, which are strictly enforced by the police to achieve the high levels of compliance required for successful operation.
• Sensors detect the speed and flow of traffic travelling on the motorway. When the onset of congestion is predicted, the speed limit is automatically reduced to 60mph or 50mph before critical flow is reached. The limit is then raised when traffic flow improves.
• Automatic queue detection and protection system that sets 40mph speed limits to protect queuing traffic and automatically sets text messages to explain to drivers the reasons for the reduced speed limits.

Plans for the future

• Extension of current successful system on M25 between junctions 10-15 on to junctions 15-16.
• Possible use on other motorways with similar stop-start congestion problems.

For more information please contact the Highways Agency Press Office on 020 7921 4323/4389/4029.