The Cuilfail Tunnel in Lewes will be closed to traffic from 8pm this evening (Friday, March 9) until 6am tomorrow morning while cleaning work is carried out.
Diversion routes will be in place but East Sussex Highways has warned drivers to expect delays.
For more information call 0345 6080193.
Elsewhere, carriageway resurfacing work is due to start in Winterbourne Hollow, Lewes, on Tuesday, March 13.
The road, together with Bell Lane, will be closed to traffic for three nights between 8pm and 6am.
East Sussex Highways said a diversion route will be in place via the A2029, B2193 and vice versa.