The M23 was closed in both directions after a serious accident meant delays for hundreds of drivers heading to and from Brighton and Hove.
The driver of a Ford Transit was taken to the Royal Sussex County Hospital in Brighton with serious injuries after crashing into the central reservation at about 4.30pm.
He was heading north at the time and the crash caused damage to both sides of the road over a 200-yard stretch.
The road was closed although traffic was sent past the crash scene via the slip roads at junction 10 for Crawley and East Grinstead.
Drivers were being advised to avoid the M23 until further notice although the delays affected people trying to reach Gatwick airport.
The Highways Agency said that the road would be reopened as soon as possible although this could take some time.
Sussex Police said at 6pm that its investigation was in its early stages and that there was no information about any other casualties at that stage.
Any witnesses are asked to call Sussex Police on 101.