The A27 Brighton bypass was closed as emergency crews dealt with a crash in the early hours of this morning (Sunday 1 July).
The westbound side of the road was shut from the Hangleton and Portslade turn-off, where the A293 link road joins the bypass, past the Holmbush shopping centre to the Adur flyover in Shoreham.
Diversions were set up, sending drivers along the Old Shoreham Road.
Inspector Keith Stoneham, of Sussex Police, said that an accident investigation was taking place but declined to give any information because, he said, it would lead to speculation.
The Highways Agency said that the stretch of road, which includes the Southwick Tunnel, was expected to reopen at about 7.15am.