A driver from Storrington suffered serious injuries in a crash on the A27 near Chichester, police said.
Sussex Police issued an appeal for witnesses and dashcam footage after the crash which happened on Wednesday (13 December) at about noon.
The force said: “Police are appealing for witnesses and footage following a collision on the A27 near Chichester.
“Emergency services were called to the westbound carriageway at Southbourne at about midday on Wednesday 13 December.
“The collision involved two vehicles, a silver Peugeot and a Volkswagen Transporter.
“The driver of the Peugeot, a 66-year-old man from Storrington, sustained serious injuries and was taken to the Southampton General Hospital, where he remains.
“The driver of the Volkswagen, a 27-year-old man from Brighton, was not injured.”
Detective Sergeant Rosie Newman, from the Serious Collision Investigation Unit, said: “This was a serious collision and we are appealing for witnesses to come forward.
“In particular, we would like anyone with dashcam footage of the vehicles either during or in the run up to the collision to come forward.”
Sussex Police said: “Information can be reported online, on 101 or by emailing collision.appeal@sussex.police.uk, quoting Operation Abbotstone.”
