A woman passenger died after the Porsche car she was travelling in left the road and hit a lamppost.
Joanne Collins, 34, of Worthing, died from her injuries after the smash on the A283 Steyning road under the Shoreham bypass on Wednesday night.
The 45-year-old driver of the Porsche Carrera, who lives in Portslade, received minor injuries.
The victim is believed to have died soon after she was taken to Royal Sussex County Hospital in Brighton.
The driver of the car did not require hospital treatment.
Sergeant Marcus Stuart, of Shoreham traffic police, said: "This was a very nasty crash.
"An investigation has been launched and we must wait for this to be completed before we can give a full explanation of what happened.
"We have still to confirm the relationship between the two people in the car. We are appealing for witnesses to come forward."
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