Worthing police are hunting a van driver who hammered on a woman's car and shouted abuse.
He had been tailgating the woman's Ford Escort before the attack on the A24 in Findon Road, Worthing.
A police spokesman said: "The van overtook and pulled up sharply in front her close to the Kings Parade shops.
"After assaulting her the man drove away at high speed."
The blue Ford Transit van is described as a builder's or decorator's van.
Police want to trace a woman who came to the victim's aid and said she knew the van driver.
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