The new year will mark the start of £14.8million improvements to the A259 in a bid to reduce severe congestion.
Single-carriageway sections of the busy A-road between Angmering and Littlehampton will be dualled, alongside other improvements by West Sussex County Council.
But before the bulk of the works can start, around four months of preparation will begin early next month.
Roger Elkins, county council cabinet member for highways and infrastructure, said: “This is essential preparation work ahead of the major A259 improvements scheme to widen around 2km of single-lane road to dual carriageway.
“A lot of future housebuilding and commercial development is planned for north of Littlehampton and this will increase the current traffic issues on the A259.
“The improvement scheme will reduce congestion and so cut both journey times and pollution.”
Weather permitting, clearance of vegetation and trees will start on January 7.
This is so pipework and other utilities can be moved and protected as the scheme progresses.
None of the trees being cleared are subject to tree preservation orders and a replanting scheme is being designed.
Work will take place between the Haskins garden centre roundabout and Station Road, Angmering, and the Body Shop roundabout and Highdown Drive, Littlehampton.
Minimal traffic control should be needed, a county council spokesman said.
The major works are set to start in mid to late 2019.
The first section of road widening will be from the new junction east of Wick roundabout, where the new Lyminster bypass and Fitzalan link road join the A259. This section will end at the Body Shop roundabout.
A new pedestrian and cycling path will be built to the south, separated from the road by a verge along much of the route. Minor alterations will be made to the Body Shop roundabout to take the new, wider approach into account.
The second section will be from the Station Road roundabout in Angmering to the A280 roundabout.
This will feature a new cycling and pedestrian route to the south, separated from the main carriageway by a verge.
The scheme is being funded by the county council and Coast to Capital Local Enterprise Partnership.