A teenager from Boston was flown to Hull Royal Infirmary by air ambulance this morning (Friday) after a collision closed the A153 about three miles south of Horncastle.
Police were alerted to the incident near Dalderby just after 7am. Emergency vehicles rushed to the scene.
According to police, the 18-year-old suffered suspected head and internal injuries.
He was driving a Toyota car.
No other vehicles were involved in the incident.
It is understood the road was still closed at 9am.