The A27 eastbound at Falmer has re-opened after an earlier accident.
The incident involving two cars and a motorcycle happened just before the B2123 The Drove junction.
Sussex Police said the accident happened at around 12.45pm.
A police source said: "A man came off his bike and hit two vehicles. An air ambulance was called. The Falmer and Hollingbury slip roads were closed both-ways.
"The man has serious injuries but they are not life threatening. He was taken to the Royal Sussex County Hospital by ambulance in the end."