Police are appealing for witnesses following a road traffic collision near Markyate in the early hours of Sunday.
At around 4.30am, police were called to reports of a blue Mercedes in collision with a pedestrian on the northbound carriageway of the A5183 north of Markyate.
Emergency services rushed to the scene and a man in his 20s was taken to hospital. He is currently in a stable condition.
Sergeant Russ Jones from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit, said: “We are appealing for anyone who may have seen the vehicle or the pedestrian at the time of the collision, or a short time before, and in particular anyone who has dashcam footage.
"This information will help us establish what happened.”
Anyone with information is asked to contact Sergeant Jones on 101 quoting reference Op Molong.