A car and the male pedestrian were in collision on the westbound carriageway just after 12.30am.
His next of kin has been informed.
The man was held on suspicion of causing death by careless driving while under the influence of drugs.
The road remained closed while crews and accident investigators attended the scene, causing long delays.
It reopened around 8am.
Police are appealing for witnesses who have not already spoken to police to contact them on 101.