Caerphilly County Borough Council has announced roadworks on the A472.
From Friday May 20, a temporary one-way system will be operation between the Royal Oak and Cwm Du roundabouts in Ystrad Mynach.
The council has said the works are necessary ready for the opening of the new Ysbyty Ystrad Fawr hospital later this year.
The temporary one-way system is likely to be in place for eight weeks.
Motorists are advised that A472 eastbound movements will continue as normal from the Royal Oak roundabout towards the Cwm Du roundabout.
For A472 westbound traffic, a diversion will be in place from the Dyffryn Industrial Estate roundabout to the Coopers Arms Pub traffic lights and along Caerphilly Road to rejoin the A472 at the Royal Oak roundabout.