Eight cars collided on the eastbound carriageway at 7.44am, leaving one woman with a minor neck injury and causing major tailbacks.
A police spokesman said: “This looks as though it may have been initiated by a not particularly clever piece of driving by the driver of small black hatchback who didn’t hang around to view the result.
“We’d like a little chat with them.”
Anyone who witnessed the incident is asked to call Sussex Police on 101 quoting serial 187 of 18/01.