The Welsh Assembly Government will be closing a section of the A470 to motorists to enable emergency repairs.
The trunk road, which is under the control of the Welsh Assembly Government, will be closed between the Navigation Park turn-off and the Abercynon roundabout from 12.01am to 6am on January 20.
The order has been made to protect road users and the workforce as essential work is carried out.
All vehicles, with the exception of emergency vehicles, must use the alternative route, which will see them exiting the A470 at Navigation Park and taking the second exit at the B4275 roundabout.
They can then rejoin the A470 by taking a right some 250 yards after the roundabout, and following the A4054 northbound to the roundabout with the A472, following the road eastbound before rejoining the A470 at Abercynon roundabout.
