Road signs on the M25 will tell drivers how long their motorway journey is expected to take.
The signs went live on Friday
The Highways Agency will use existing electronic signs to list estimated travel times to M25 junctions ahead.
The service is already in operation in the West Midlands and the South West, where 89% of motorists support its use.
Roads minister Tom Harris said it would help drivers to "consider options such as changing their route or taking a break if there were traffic delays".
"We are making best use of our technology to help drivers find out about traffic conditions on their route both before they leave and during their journey," he said.
The service came into operation on Friday.