|Distance:||9.3 miles (15 km)|
|Meets:||A4109, A465, B4434|
|Route outline (key)|
The present B4242 follows the Vale of Neath downstream from Pontneddfechan. It starts on the Neath side of the boundary between Brecknockshire and Glamorgan, at the bridge over the River Nedd Fach at Pontneddfechan which today marks the boundary between the Powys and Neath Port Talbot principal areas.
The road follows a southwesterly course down the Vale of Neath, on the right bank of the river and on the route formerly taken by the Heads of the Valleys Road, the A465 (now removed to a new dual-carriageway alignment closer to the centre of the valley floor).
Within 2 km of its starting-point the B4242 enters Glynneath, where it crosses the A4109 at a signalized junction. At the far end of the village a short spur connects to the new route of the A465 at Blaengwrach, while halfway along the remaining 10 km a junction with the north-eastern terminus of the B4434 provides another link to the A465. The B4242 ends at Aberdulais, 3 km northeast of Neath, where it once again meets the A4109 (that road having meanwhile looped around via Seven Sisters and Crynant).
As already mentioned, the major part of this road – below Glynneath – follows the original line of the A465. However, the B4242 started life, in the 1940s, as no more than the first 1700 m of the present route: from the Angel Inn by the bridge over the Nedd Fechan to a junction with the A465 (which at that time ran along Aberdare Road and the High Street) in Glynneath.