A person suffered life-threatening injuries in a crash that shut a stretch of the M25 in Surrey.
Two other people were also taken to hospital with serious injuries, National Highways said.
The crash took place between Junctions 8 and 7 on the anti-clockwise carriageway near Reigate at 23:45 GMT on Thursday.
The road was closed, with one lane re-opening at 05:00 on Friday. Two lanes remained shut.
National Highways said the lanes were shut while a damaged barrier underwent repairs. Motorists were told on Friday morning to expect "severe delays" of up to 90 minutes.
The spokesperson said: "We know this is having a significant impact on many journeys and encourage drivers to allow extra time and plan ahead."