A 20-year-old woman and a 23-year-old man have been arrested in relation to the crash.
The collision which happened late last night tragically killed a 25-year-old man.
The road has remained closed for most of the day causing disruption to the roads.
His passenger – a 19-year-old man also from Havant – suffered life-threatening injuries and has been taken to hospital.
Sussex Roads Police say "thank you for your patience and understanding. Pease contact us if you have any information".
Call 101 or email collision.appeal@sussex.pnn.police.uk quoting Operation Westdown.
This is the statement from the police:
"A black Volkswagen Golf was travelling east towards Chichester, on the Sussex /Hampshire border, when it crashed into the central reservation about 11.40pm.
"The driver – a 25-year-old man from Havant – was sadly pronounced dead at scene.
"The sole passenger – a 19-year-old man from Havant – suffered life-threatening injuries and has been taken to hospital for treatment.
"A 20-year-old woman and a 23-year-old man, both from Havant, have been arrested on suspicion of causing death by dangerous driving, and remain in police custody at this stage.
"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."
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