Heads of the Valleys road widening increases by £54m
The cost of widening the A465 Heads of the Valleys road will cost an extra £54m, it was announced on Wednesday.
The Welsh Government is turning the 30-mile stretch of the A465 between Abergavenny and Hirwaun into a dual carriageway.
It has said the primary cause of the cost increase was "complex" work on a five-mile section in the Clydach Gorge.
The expected December 2019 completion date will also be missed, the government said.
The project was originally planned to cost £220m but that rose in November 2017 by over £50m.
It has been announced that a further £54m will be added to the overall cost, taking the total to an estimated £324m.
In a statement, the Minister for Economy and Transport, Ken Skates, said he was disappointed that the project would not be completed on time.
He said: "The project has experienced delays and cost increases due to difficulties experienced on site."
Work being done includes widening the steep-sided and environmentally sensitive gorge.
Mr Skates said contractor Costain had highlighted "a complex construction solution required to address the geological feature that they have discovered in one particular location".
In June 2018, Wales' public spending watchdog, the Wales Audit Office, also began an audit of the project's commercial position. It is expected to pass its initial findings to ministers soon.