The road had been closed off in both directions from the Havant Road junction in Warblington up to Fishbourne Roundabout for Chichester following the crash at 11.40pm last night.
A black Volkswagen Golf was travelling east towards Chichester when it crashed into the central reservation.
The driver – a 25-year-old man from Havant – was pronounced dead at scene, while the car’s passenger – a 19-year-old man from Havant – suffered life-threatening injuries and has been taken to hospital for treatment.
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Now police have arrested a 20-year-old woman and a 23-year-old man, both from Havant,on suspicion of causing death by dangerous driving.
They are in police custody.
A spokesman from Sussex Police said: ‘The road was closed in both directions while investigations were carried out, and has since reopened. We’d like to thank the public for their patience and understanding.’
Police are appealing for witnesses and are particularly interested to hear from anyone with dash cam footage of the collision, or the Golf or a red Audi A3 being driven in the area prior to the collision.
Anyone with information is asked to contact police on 101, quoting the reference Operation Westdown.