Motorists faced four miles of congestion following a collision on the M25.
National Highways said two of the four lanes were closed on the anti-clockwise stretch in Hertfordshire between junction 24 at Potters Bar and junction 23 at South Mimms.
A recovery vehicle was sent to the scene.
At 07:01, the agency said all lanes reopened, but there was still a 50-minute delay for drivers.
