A 51-year-old lorry driver from Uckfield suffered serious injuries in a collision on the A22 in Maresfield.
The collision happened at 6.15am on Tuesday (November 5). An air ambulance was sent to the scene and the road was closed for several hours.
A spokesman for Sussex Police said: “We are appealing for witnesses to an incident on the A22 at Lampool roundabout, Maresfield, in which a lorry driver sustained serious head injuries.
“A blue Mercedes-Benz Antos 18-tonne flat-bed lorry and a grey Volkswagen Crafter CR35 van both came to an abrupt halt while negotiating the roundabout.
“The lorry driver, a 51-year-old man from nearby Uckfield, got out his cab to speak to the van driver, a 27-year-old man from Hailsham, and while on foot was in collision with a grey Citroen Picasso, driven by a 67-year-old man from East Grinstead.
“He was taken by ambulance to the Royal Sussex County Hospital, Brighton, where he is being treated for potentially life-threatening injuries.
“The A22 and other roads feeding into the scene were closed for almost five hours while the incident was dealt with.
“Police would like to thank motorists who were affected by delays and diversions for their patience and understanding.”
Anyone who saw what happened, noticed any of the vehicles being driven shortly before the collision or who may have dash-cam footage is asked to contact Sussex Police online or call 101, quoting Operation Drybrook.