The accident happened shortly after 6 a.m. on the B2112 New Road between Ditchling and Clayton.
Anyone who witnessed the incident or captured it on dash cam is asked to email [email protected] quoting Operation Kempston.
Officers are particularly interested in hearing from anyone who sees a white van, possibly with a 2015 licence plate, with damage to its headlight and a missing nearside wing mirror.
At this time, a section of the road remains closed, and motorists are advised to seek alternate routes.
