The N24 re-opened overnight between Kilsheelan and Carrick on Suir following a collision yesterday afternoon.
The crash – involving a car and a truck – happened at Ballydine.
The driver of the car – a man in his 30s – was airlifted to Cork University Hospital where he is being treated for serious injuries.
The road was closed for a number of hours to allow forensic collision investigators carry out an examination of the scene.
Gardaí in Clonmel are appealing for witnesses or anyone who has dash-cam footage to contact them on 052 6177640.