The M23 was closed near Gatwick Airport for about 10 hours after a pedestrian died in a crash involving a van and a lorry on the motorway.
It happened at about 01:00 GMT, between junctions 8 (M25) and 9 (Gatwick).
Sgt Dan Pascoe, from Surrey Police, said: "The circumstances behind this collision are unclear at the moment."
The force is asking anybody on the road around that time to get in touch if they witnessed anything, or have any useful dashcam footage.
The section of the M23 reopened at about 11:00 GMT, Highways England later confirmed.