A woman was cut free after a car overturned in a crash on the A23 just to the north of Brighton.
She, two other women and a man were taken to hospital by ambulance after the crash at Albourne on the southbound stretch of the road between the A2300 at Hickstead and the A273 at Pyecombe.
Firefighters from West Sussex Fire Service cut the woman out of the car after she became trapped in the crash.
The road was closed for almost four hours while paramedics, firefighters and crash investigators worked at the scene.
Initially only one vehicle was reported to have been involved in the crash which happened at about 4pm yesterday (Saturday 20 January). An update said that two cars collided.
Separately, the M23 remained open this weekend – despite electronic signs saying the opposite – as bad weather led to roadworks being postponed.
Highways England said: “Junctions 10 to 9 weekend closure of the M23 has been postponed due to a forecast of heavy rain.
“The M23 near Gatwick Airport will be open as normal.”
The southernmost stretch of the motorway was closed all weekend last weekend while train services were also affected by engineering works, making trips to and from Gatwick much harder.
The weekend closures are expected to resume next weekend.