Roadworks will take place on the A38 Mardle Viaduct near Buckfastleigh.
Highways Agency chiefs will be re-waterproofing the westbound carriageway of the viaduct from September 26 to October 23.
While work is taking place one lane of the westbound carriageway on the viaduct will remain closed 24 hours a day.
The remaining lane will be narrowed to allow the work to be carried out safely – a 40mph speed limit will also be in place.
The adjacent slip roads on to the viaduct from Dart Cross Bridge and Peartree junction will be closed to allow traffic to slow down through the single lane.