The scheme was proposed in the 1990's to widen the original 1960's single carriageway to 2 lanes in each direction because of a high number of collisions on the road, the first bit of the scheme to open to traffic was from Tredegar - Dowlias Top in 2004 next was the section from Abergavenny - Gilwern in 2008 then the next to open was Brynmawr - Tredegar section in 2015 then the most recent to open was the section from Gilwern - Brynmawr in late 2021 and the next to open (which is currently being constructed) is the last section from Dowlais Top - Hirwaun in 2025.