Stockbridge Road has been reopened to traffic after an earlier signalling fault closed the level crossing.
Traffic was diverted via Whyke Road while the Stockbridge level crossing remained closed.
At the scene, a member of Land Sherrif Ltd, which provides security for Network Rail, confirmed the level crossing closure was due to a signalling fault between Littlehampton and Chichester this morning.
He said the fault was first reported at around 1.30am and the Whyke Road level crossing was being controlled manually to let traffic through.
In a statement on its website, Network Rail confirmed the fault was a 'track circuit failure', where the signalling system is unable to automatically verify if the next section of track past the affected signal is clear.
The line was closed between Barnham and Havant from 11.30am to 12,30pm while repairs were carried out.