PART of the A465 in Merthyr Tydfil will be closed for five weeks this summer for works to be completed.
The road between A470 (Cefn Coed) junction and the temporary roundabout at Pant Industrial Estate will be fully closed from July 29, with a diversion in place.
Welsh Government said this is to allow for important work to be completed sooner and with less uncertainty for the travelling public.
The closure will start at 6am on Monday, July 29 and will end at 6am on Monday, September 2 and is taking place during the school summer holidays when there is less traffic on this section.
The closure will allow several important elements of the A465 work to progress, helping save time on the construction programme and removing the uncertainty to journey times which overnight and weekend closures can cause, the Welsh Government said.
It said that feedback from the public indicates constant change, such as overnight and weekend closures, are more disruptive than a fixed closure with a clear diversion.
The diversion in this case will be around four miles longer, but the journey time should be under five minutes longer only, the Welsh Government added.
The A465 between the Dowlais Top junction and the Pant Industrial Estate temporary roundabout will still be open, but only for local traffic.
Welsh Government said that discussions have taken place with partners including the local authority, Prince Charles Hospital and the emergency services before the decision was taken.
The closure and the work is being managed by Future Valleys Construction.
The work being carried out during the closure includes removing the old bridge at Bryniau, construction of a new bridge at Bryniau, constructing a new highway embankment for the eastbound carriageway at Gurnos, progressing work to construct the new of Prince Charles Hospital junction, integrating all sections of road and the footway over Taf Fechan viaduct and completing the carriageway through Cefn Coed and over Taf Fawr viaduct.
More information is available on the Future Valleys Construction website.
