A 21-year-old Dunstable man was airlifted to the JR2 Hospital in Oxford with head injuries after his car and a lorry were in collision on Monday evening just after 6pm.
His Ford Fiesta had broken down on the Stoke Hammond bypass.
The driver of the lorry, a 30-year-old man, was arrested on suspicion of dangerous driving and has been released on bail until August 12.