For the next 15 miles (24 km) it is a modern high-speed dual carriageway by-passing Tongwynlais and Castell Coch, Taff's Well, to Pontypridd.

Heading north to Abercynon, the road now follows the route of the Taff Vale Railways Llancaiach Branch to Quakers Yard roundabout,[3] where it is joined by the A4059 from Abercynon, Aberdare and Hirwaun; the A472 from Ystrad Mynach and Pontypool finally the A4054 from Quakers Yard, and Merthyr Tydfil.

This artificiality is apparent as a driver following the entire route north to south must diverge from the main line of respective stretches of road no fewer than five times.

A short three lane stretch heads north east before a sharp left turn is required to stay on the road.

Another sharp left turn at a stop sign in Llyswen takes the road alongside the River Wye into Builth Wells.

On reaching Llangurig, a right turn outside the village takes the road past Llanidloes and through Llandinam, the birthplace of David Davies and now the headquarters of Girl Guides Wales.

Another anomalous left turn at a level crossing sets the path for Caersws, Carno and Llanbrynmair.

The long descent towards Commins Coch is a relatively new stretch of road that replaced a set of road-works that had traffic light controlled single lane working for over 10 years because of unstable ground conditions.

The river bridge at Commins Coch is so narrow and set at such an angle that only one vehicle at a time can pass.

The country becomes more forested and the road climbs up through Dinas Mawddwy and then steeply up the eastern foot-hills of Cadair Idris before dropping down to the Dolgellau by-pass.

It was successful, and in 1978, the Welsh Office discussed a potential course of the road roughly through the centre of the country, which was implemented the following year.

Cross Foxes to near Gellilydan (in the Meirionydd part of Gwynedd south of Ffestiniog) brings us to a complicated series of route renumbering.

In 2014, Cerys Matthews presented a documentary on the A470 on BBC Radio 4, journeying from the north of the country to Cardiff Bay.