Commuters and motorists can expect massive traffic delays on the A24 southbound carriageway during repair work which begins on Sunday.
One lane of the dual carriageway will be closed for two weeks from Sunday, November 11.
The inside lane of the southbound section of carriageway is being shut so urgent parapet and fencing work can be done at Hole Street in Ashington.
It will affect about 500 metres of the southbound Ashington bypass.
There are already big tailbacks of traffic on the road when both carriageways are in use at peak commuting times.
Queues sometimes extend as far back as Hole Street.
West Sussex County Council says the work is necessary to ensure the carriageway remains safe for the public to use.
The closure will be in place 24 hours a day until the lane is re-opened.
The £75,000 scheme is being carried out by West Sussex County Council’s highways contractor, Balfour Beatty.
County Council Cabinet Member for Highways and Transport, Pieter Montyn, said: “We apologise in advance for the inconvenience this may cause.
“In case of delays during this period, we advise people travelling along this stretch of the A24 to allow more time for their journey.”