Drivers are facing delays on one of the busiest routes between Burgess Hill and Haywards Heath.
Parts of Rocky Lane near the Haywards Heath end have been reduced to a single lane and traffic lights introduced.
There are also traffic lights at the junction of the new estate off the road.
New 30mph limit sign signs have also been put up.
Groundwork has started on land next to the road and disruption is expected for about 20 weeks.
Eventually a new roundabout, link road from the Bolnore estate, and bridge across the London to Brighton rail line will be built.
More housing is also earmarked for the land on the east of Rocky Lane.
No date has yet been confirmed for a start on the multi-million scheme to build a new bridge across the railway line.
Developers Crest Nicholson have said that the new road is planned to open in summer of 2015.
The road from the Bolnore estate will loop slightly eastwards returning to Rocky Lane.
Drivers are also waiting for the completed section of the relief from Wivelsfield Road to near the Birch Hotel at the A272 to be opened.