Appin Road will close for three days next week for maintenance.
The closure - between the M1 and Appin township - will occur on September 17-19, between 9am and 3pm.
Motorists travelling between Wollongong and Campbelltown can detour via Picton Road and the Hume Motorway.
Light vehicles can also use Broughton Pass between Appin and Picton roads.
Roads and Maritime Services expects the detours will add up to 15 minutes travel time to a trip.