The B6270 between Low Row and Gunnerside was closed for around five hours following the incident at 11am on Thursday, when a Ford Mondeo left the road between Low Row and Gunnerside near Richmond.
North Yorkshire Police said the car had come to rest approximately 50 metres from the road in a field.
The driver, a man aged in his 30s from the Darlington area, suffered serious injuries and was airlifted to James Cook Hospital in Middlesbrough where he remains in a critical condition. The passenger in the car, a 17- year-old boy, also from the Darlington area, sustained less serious injuries and was taken to Darlington Memorial Hospital.
Investigators examined the scene of the collision for several hours yesterday.
Anyone who witnessed the collision is asked to contact North Yorkshire Police on 101, select option 2 and ask for Richmond Roads Policing Group, or email [email protected]
Quote reference number 12170231022.