A tunnel near the A27 is set to close overnight.
The Cuilfail Tunnel on the A26 in Lewes will close on June 7 from 8pm until 6am.
East Sussex Highways said this is for routine maintenance work.
A diversion will be in place via A27, Brighton Road, High Street, Market Street, Little East Street, and Phoenix Causeway.
A spokesman for the East Sussex Highways team said: "We are very sorry for any inconvenience caused."
The name of the tunnel, which opened in 1980, comes from the Cuilfail area of Lewes.
It is a single-carriageway tunnel through the chalk hillside leading to the A27.
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The closure comes at the same time as the full weekend A27 closure in Lancing.
This will start at 9pm on June 7 and will end at 6am on June 10.
It is the fourth full weekend closure to take place on the busy A-road, which is currently having a new roundabout built for the New Monks Farm housing development.
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