|Length:||9.4 miles (15.1 km)|
|Meets:||B4487, A48, B4237|
|Route outline (key)|
The B4239 is a coastal B-road in south Wales. It was originally unclassified but gained its number in 1935.
The road starts in Rumney, now essentially a suburb of Cardiff, at traffic lights on the B4487 (former A48). It heads south along the residential Wentloog Road, gradually bearing leftwards before an unsigned TOTSO right then left takes the road over the railway line and through an industrial estate to reach a T-junction where we TOTSO left. The unclassified road to the right is signed as the main road, presumably allowing traffic to avoid Rumney; it quickly meets the A4232.
We now head northeastwards across the flat coastal plain passing a few warehouses and crossing two roundabouts before bearing right at a third. This is where we rejoin the original route of the B4239; that continued east along Wentloog Road (avoiding all the TOTSOs before crossing the railway line and coming in from the left here. Although the railway bridge still exists albeit closed to traffic the road has had warehousing built on top of it on this side of the railway and following the route, even on aerial photos, is very difficult.
Now wholly rural we continue across the marshes, with the Bristol Channel to the right but not visible. We do pass a few buildings and presently reach the scattered village of Peterstone Wentlooge. Here the road zigzags inland before continuing in the same direction to St Bride's Wentlooge, which is more compact. The road now becomes more winding and shortly turns inland. The railway line is crossed again, then we skirt the Newport suburb of Duffryn. The road is not built-up for long before we bear left (the road's original route was severed when the A48 was built) then turn right at a roundabout to end at another roundabout on the A48. The B4237 continues ahead into the city centre.