Council repairs to a retaining wall on the A472 just north of Hafodyrynys are causing traffic delays.
Caerphilly County Borough Council said the wall on the left hand side as you travel towards Pontypool was unsafe and had to be demolished.
The council has said the works could take six weeks or more, but that every effort was being made to reduce disruption.
Cllr Rob Gough, cabinet member for public protection, engineering and transport, said: “We understand the A472 is a main thoroughfare for commuters both to Pontypool and Newport but these works are essential to remove the risk of the wall collapsing onto the road. We cannot remove the traffic controls due to the risk of falling debris from the exposed earth and rock face. Additional measures are being implemented to try and keep traffic build up to a minimum and the situation is being monitored.”
Drivers are asked to avoid the route if possible and the council will work as quickly as they can to resolve the problem, but commuters can expect delays until the end of August.