Another lane will be added to the Heads of the Valleys road between Bryn Mawr and Tredegar.
It follows the announcement of almost £82 million of European funding.
The A465 dualling scheme will see improvements to the 7.8km route which extends from the north of the A465 roundabout at Brynmawr and tie in with the previously improved A465 at Tredegar.
The work is likely to start early next year.
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Variable cloud and clear spells overnight with isolated showers mainly in the north.
Becoming drier and brighter from the northwest during the day, but with the risk of scattered, locally heavy, showers developing later.