Police are appealing for witnesses after a car hit the rear of a parked lorry on the A23 at Hickstead on Sunday evening (18 August).
The Renault Scenic was travelling south when the collision occurred as the HGV was parked in a layby at 8.40pm. The front seat passenger, an 18-year-old man, suffered serious injuries and was taken to the Royal Sussex County Hospital, Brighton. His condition is critical.
The driver of the car, an 18-year-old man from London, suffered minor injuries and was later arrested on suspicion of dangerous driving. He is currently in custody. The lorry driver was unhurt.
Sergeant Dan Eaton said: "We would like to hear from anyone who saw this serious injury collision or has any information about it. The road was closed for several hours last night while we carried out an investigation and we would like to thank drivers for their patience."
If you can help with the investigation report online or ring 101 quoting Operation Beaufort.