A woman has died and a man has been left with serious injuries after a collision on the M23.
Police have shut the northbound carriageway and are investigating the single-vehicle collision, which happened just before 5am on Thursday between junctions nine and 10.
The driver of the car, a 21-year-old man from London, has been arrested for causing death by dangerous driving and causing serious injury by dangerous driving, Sussex Police said.
The car left the main northbound carriageway during the incident, the force said.
One passenger, a 23-year-old woman, was pronounced dead at the scene. A 23-year-old man who was also a passenger is being treated in hospital for serious injuries.
"This is a tragic incident, and we are actively investigating the full circumstances of what happened," said Inspector Matt Wightwick.
Police said the woman's family has been informed and the northbound carriageway will remain closed while the vehicle is recovered and an investigation is carried out.
"It will be opened as soon as it is safe and practical to do so," Sussex Police said.
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The incident led to queues that were over four miles long and waits of more than an hour.
A diversion has been put in place, with National Highways advising drivers to exit the M23 at junction 10 and initially follow the A264 eastbound.
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