The M25 in Hertfordshire has become England's first section of motorway without a permanent hard shoulder.
An eight mile section of the hard shoulder between junctions 23 for the A1 and junction 25 for the A10 will be available from this week.
The new 'smart motorway' scheme aims to reduce congestion and ease traffic flow, improving the reliability of journeys.
Overhead gantries will display a red 'X' to clear a lane if there is an incident ahead, the Highways Agency said.
One more section on the southern part of the M25 is due to open next month, with a third later in the year on the northern section, with similar schemes being rolled out across the country including the M1, M3, and M62.
An estimated 1.1 million man hours have gone into converting this section of the road into a smart motorway.