A crash closed a stretch of the M25 in Essex for seven hours on Wednesday.
A Fiesta, Mini and BMW collided on the anti-clockwise section between junctions 30 and 29 in Basildon at 1830 BST.
The passenger in the Mini, a 23-year-old woman from Chelmsford, is in hospital in a critical condition. The Mini and BMW drivers were not injured.
The Fiesta driver, a 32-year-old Basildon man, was arrested at the scene on suspicion of dangerous driving.
The section of the M25 was closed while investigators examined the scene and diversions put in place.
