Special Highways Agency jam-busters will now patrol the whole of the M25 London orbital road.
The latest service, between J14 London Heathrow and J17 Rickmansworth, Herts, was introduced on Monday.
The patrols began between J2 and J14 last August and extended to J17 and J30 as the service moved into Essex in October and Herts in January.
Their responsibilities include cleaning up after accidents, moving abandoned vehicles and closing roads temporarily.
The 117 miles of the M25 will be patrolled by 50 traffic officers, in two-person crews on three shifts.
By the end of 2006, the Highways Agency Traffic Officer Service will operate 24 hours a day on 319 miles (513 km) of road, on the M25, the A1, the M1, M11, M10, A14 and the A405.
Roads Minister, Dr Stephen Ladyman, said: "By the summer around 1,500 staff based on-road or in one of seven regional control centres will be managing our entire motorway network, in an effort to ease congestion and improve journey times."
The on-road patrols are supported by staff at two regional control centres in Godstone, Surrey and South Mimms, Hertfordshire, who also answer emergency roadside telephones.