Roadworks which have created weeks of traffic jams should be completed by the end of this month.
The final phase of the improvements on the A23 near Preston Drove in Brighton, starts on Monday.
It involves resurfacing the road using high quality materials to improve skid resistance and reduce tyre noise.
Temporary traffic lights and diversions will be in place for about two weeks, including weekends.
Drivers are being asked to find alternative routes wherever possible to avoid delays.
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