A large stretch of the A27 will be closed overnight for around two months so the Stockbridge Footbridge can be replaced.
Highways England is carrying out the work, and will close the A27 from the Fishbourne to the Bognor roundabout from Monday, January 8.
The road will be closed from 8pm to 6am during weekday nights until mid March, when the work is scheduled to be completed, Highways said.
A temporary crossing for pedestrians is being installed this week while the old footbridge is being removed and a new one installed.
From Saturday, January 12 at 6am, there will be a 24-hour speed restriction of 50mph for the duration of the works, as well as a dedicated slip road closure on the westbound carriageway at Stockbridge roundabout.
The work was due to take place in September last year, but Highways delayed the project to make design changes.
The old A27 footbridge at Stockbridge will close until its new replacement is erected and opens.