Police are appealing for witnesses after a collision on the A264 near Horsham on Sunday (December 3).
Officers were called to the incident at about 3.30pm on the eastbound carriageway, between the Rusper Road roundabout and the Moorhead roundabout.
It involved a turquoise Volkswagen ID3 that left the carriageway.
A man and a woman from Horsham sustained serious injuries and remain in hospital at this time.
The road was closed while police carried out an investigation. It has since reopened.
Officers are appealing for witnesses or anyone with relevant information such as dashcam footage of the vehicle and other vehicles in the area at the time to come forward.
Information can be reported to Sussex Police by emailing collision.appeal@sussex.police.ukand quote Operation Smallbrook.