M25 speed limit controls extended to Kent
Variable speed limits are being introduced on the M25, near the Dartford crossing in Kent.
The Highways Agency said the system, already used on the motorway in Surrey and near Heathrow, was being introduced at Dartford from Wednesday.
Senior project manager John Martin claimed the move would help to reduce congestion and make journeys safer.
The speed limits are being brought in between junction 2 for Darenth and junction 3 for Swanley.
Mr Martin said the system would allow the agency to manage traffic flow during peak congestion, or following an incident, by varying speed limits to smooth out traffic and reduce the risk of further collisions.
He said: "On the M25, where the system has been in place since 1995, it has reduced collisions by 10% and provided the benefit of smoother, more reliable journeys at peak times.
"In addition, an overall reduction in vehicle emissions of between 2% and 8% has been recorded on the M25."
The system uses sensors in the road surface to detect the speed, volume and flow of traffic and calculates the best speed to keep the traffic moving.
The speed limit appears in a red circle, which means it is enforceable by law, on electronic overhead signals.
Kent Police will be using cameras to enforce the speed limits, the Highways Agency said.