Sussex Police are appealing for witnesses of a single vehicle collision involving a 4x4 on the A24 Findon bypass near Worthing at around 8.30pm on Thursday (August 19).
The driver, a 28-year-old man, was taken to Royal Sussex County Hospital in Brighton with serious injuries.
Anyone who has any information about the collision or has dashcam or CCTV footage is asked to email collision.appeal@sussex.pnn.police.uk, quoting Operation Tackle.