Police are appealing for witnesses after a man was airlifted from the scene of a crash on the Stoke Hammond Bypass on Monday night.
The emergency services were called shortly after 6pm after reports of a collision involving a blue Ford Fiesta, which had broken down on the carriageway and had been in collision with a lorry.
The driver of the Fiesta, a 21-year-old man from Dunstable, was airlifted to the JR2 Hospital in Oxford with head injuries. The driver of the lorry, a 30-year-old man, was arrested on suspicion of dangerous driving and was released on bail until August 12.
Anyone with information should contact the non-emergency number 101.