Lincolnshire police are looking for witnesses after a single-vehicle collision on the A46 Lincoln bypass.
The incident happened just before 2.45am on September 10, between the Skellingthorpe and Doddington roundabouts on the A46.
A silver Vauxhall Vectra left the road and collided with trees at the side of the carriageway.
The 30-year-old local driver is at Queen’s Medical Centre in Nottingham, where he is currently in the Intensive Care Unit.
The bypass between the two roundabouts was closed until around 6.50am while removal and investigations took place.
If anyone saw the vehicle leave the road or before the collision, contact the force on 101 or leave a message on the witness hotline, 01522 558855.