Motorists faced rush-hour diversions after a car reportedly ploughed into a tree.
One man has been arrested in connection with the incident on the A689, in Belle Vue Way, Hartlepool, with police suspecting that other occupants may have fled the scene.
A stretch of the A689 heading out of town was closed for nearly an hour on Tuesday morning after emergency services were called.
A Cleveland Police spokeswoman said: "Police attended Belle Vue Way, near Travis Perkins, at 7.35am today where a VW Golf was reported to have collided with a tree.
"On arrival a 38-year-old man remained in the car. However, it is believed there may have been other occupants who had left the scene.
"Stockton Road to Brenda Road was temporarily closed to allow emergency services access and the man was taken to hospital by ambulance.
"The westbound carriageway was reopened at 8.25am and emergency services remain on scene.
"The 38-year-old has been arrested in connection with this collision and inquiries into the circumstances have begun."
Anyone with any information about the incident should contact Cleveland Police on 101.