Construction work on dualling of the A465 above Gilwern is 85% complete but Costain has run into unexpected problems and it will not be finished until April 2021 at the earliest, Wales economy and transport minister Ken Skates has reported.
Now plans to improve the section from Hirwaun to Dowlais are being developed but under a fixed price contract and with minimum disruption to traffic using the main road to and from the Midlands.
The biggest road project in Wales to widen the A465 through the Clydach gorge between Gilwern and Brynmawr should have been finished in 2018, four years after it started when it was estimated to cost £223M.
However, the geology in the area and the nature of the project with weekend road closures and diversions has led to a dispute between Welsh Government and contractor Costain and has now been recalculated to be about £321M.
However, the Wales Audit Office report into the delays said it was impossible to say how long the dispute would take to resolve and the uncertainty meant it was difficult for the Welsh Government to predict the final figure.