Officers were called to the M5 slipway at junction 21 at Weston-super-mare at 10.10pm on Friday to reports of a 26-year-old man having being stabbed.
Avon and somerset police said the man “suffered stab injuries” after a “dispute” with another driver.
The victim was taken to hospital with police adding his injuries are “not life-threatening”.
Avon and Somerset Police said in a statement: “The victim was a passenger in a car which had just exited the M5 at this junction and was at a set of traffic lights.
“A dispute then ensued with the driver of another car, following which the victim was stabbed.
“The offender was in a dark coloured car and we’re making urgent enquiries to locate this vehicle.
“One lane of the slip road remains closed so we can carry out a further examination of the scene.”
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