Drivers stuck in traffic for several hours are being urged to 'be patient' as further delays are expected.
A crash between two lorries and a Ford Focus happened around 7:50am this morning between junctions 40 and 41, near Penrith.
Traffic build-up soon stretched for miles in both directions.
Late this afternoon there was little evidence of the situation of easing, despite police reopening the road.
The driver of the car was flown by air ambulance to the James Cook University Hopsital in Middlesbrough after sustaining serious head injuries.
He is in a critical but stable condition. The lorry drivers were not injured.
Cumbria Police has thanked motorists for their patience during this time.
Any witnesses should contact 101.