The Tangmere Roundabout was evacuated shortly before 2 a.m. this morning due to reports of a single-vehicle collision on the eastbound carriageway.
The sole occupant of the vehicle, a 53-year-old man, was airlifted to a hospital with serious injuries.
After the road was closed for accident investigation work, traffic has returned to normal.
Police are looking for witnesses and would like to speak with anyone who saw the incident or the events leading up to it, as well as anyone who has relevant dash cam footage.
Officers are asking anyone with information to contact them at [email protected], quoting Operation Heydon.