SIGNS at the Clover Leaf Roundabout, off the A27 in Shoreham, are warning drivers to expect major delays from Monday.
Roadworks begin on the A283 to create a new right-turn for a new housing development in Sullington.
The junction improvements are expected to last for 20 weeks, finishing around August 3.
The works are in Storrington Road, between Water Lane and Hampers Lane. Two-way signals will be in operation 24-hours a day, with manual control to manage traffic flows at peak times.
There will be a temporary 30mph speed limit.
West Sussex County Council said: “Due to the location of these works, significant delays are expected on the A283, with increased traffic on the surround road network.”