Police are appealing for witnesses following a serious collision near Arundel on Sunday (August 12) at 2.35pm.
The collision happened on the A29, Fairmile Botton in Madehurst and involved two vehicles, a Landrover Discovery 4x4 with caravan and a Landrover Freelander.
However the police are looking for a horsebox that was immediately in front of the Freelander.
A 73-year-old man from Chichester, the driver of the Freelander, was taken by road to the Royal Sussex County Hospital with serious injuries.
Another 73-year-old woman, also from Chichester, was airlifted to the same hospital with serious injuries. She was a passenger in the Freelander.
Both are in a critical but stable condition today (Monday August 13).
PC Glen McArthur from the Road Policing Unit said: “The road was closed for six hours and we thank drivers for their patience while we investigated. We are keen to talk to anyone who saw what happened. Please would they contact police on 101 quoting Op Allsworth.”