A man was airlifted to hospital after his car left the A19 and hit woodland before coming to rest.
The accident happened on the southbound carriageway of the A19, near Peterlee.
The Great North Air Ambulance took the male to the James Cook University Hospital in Middlesbrough for emergency treatment.
Police, fire crews and ambulances also attended the scene but the man’s condition is not known.
Investigations to determine the circumstances surrounding the smash are underway.