Motorists will be made to go slower to get there faster on Britain's busiest stretch of motorway in a pilot scheme launched yesterday.
The scheme will be tested for a year on the western section of the M25, the London orbital motorway, between junction 11 and junction 15 where variable speed limit signals will be installed on gantries.
The idea is that if all vehicles are travelling at the same speed, there will be no bunching and lane changing and, therefore, the capacity of the road will increase.
Sir George Young, the Secretary of State for Transport, likened the effect to riding a bicycle up and down hills: "You may go faster down the hills but you will go much slower up them and your average speed will be lower than if you are cycling constantly on the flat at the same speed."
At first the speed limits will be imposed at set times of the day but once drivers have got used to them, they will be triggered by the number of vehicles using each lane. When that reaches 1,650 per hour, the limit will go down to 60mph and then to 50mph when there are 2,100 vehicles per lane per hour.
Sir George said the scheme would only succeed with the public's co-operation: "Too often drivers sit in the outside lane while the inside lane is empty or will lane-hop to try to get one step ahead."
Lawrie Haynes, chief executive of the Highways Agency which is responsible for Britain's motorways and trunk roads, said the scheme could be extended if successful.
"There are several stretches of motorway where bunching occurs such as the M1, M4, M56, and M62 and parts of the M40," he added.
The pounds 12.5m scheme will be extended to junction 10 on the M25 later this year. Similar schemes in the Netherlands and Germany have proved successful and, according to Sir George, "led to 30 per cent reductions in accident rates".
Offenders will be prosecuted through information obtained from speed cameras mounted on gantries.
Initially they will only be sent warning letters but in the next few weeks - the police refused to say when - fixed penalty notices will be sent which will involve fines of pounds 40 plus three penalty points.
However, the police said that they would not use the cameras to prosecute motorists breaking the normal 70mph, but according to a spokesman, "that may happen in the future".
The Automobile Association supported the scheme but warned that motorists should not be prosecuted if the limits had been imposed by the police, rather than automatically, at times when there was not much traffic.
Paul Watters, its head of roads policy, said: "The police-operated variable speed limit could be left in place for longer than necessary and drivers will be photographed for contravening an unnecessary and inappropriate speed limit."Reuse content