The A4230 is a short road (less than four miles long in total) which, in two sections, follows the former path of two long-distance routes through built-up areas lying to the west and north-east of the town of Neath in west Glamorgan.
Starting at the Lôn-las interchange (junction 44) of the M4 – on the ridge dividing Llansamlet in the Swansea Valley from Skewen in the Vale of Neath – it descends through the latter community, following what had been, before construction of the motorway, a section of the now-interrupted route of the A48.
At this point the A4230 also parallels the South Wales main railway line between Swansea and Neath, although the tracks (running at first in a cutting and then on an embankment) remain almost entirely out of sight of the road. Zigzagging right-left to cross over the railway at the western end of Skewen proper we now descend the fairly narrow, shop-lined New Road (a parallel Old Road lies a little to the south) – a route which is nearly always very busy with local traffic today and must have been a nightmare when this was the main A48!
At the foot of the hill, we run out of Skewen and into the adjoining district of Neath Abbey, passing the remains of the Abbey gateway on the north side of the road (our left) before encountering a double mini-roundabout. What is left of the Cistercian abbey (a surprising amount considering that the site and most of the buildings were the site of copper-smelting works and a large iron foundry for the best part of 200 years) lies to the south of the A4230, between our road and the A465 dual carriageway.
It is a part of the original route of the A465, north and north-east of Neath town centre, that the A4230 follows next. But first our route is interrupted by a stretch of the A474 (now the Briton Ferry to Ammanford road) running from a large roundabout by the Neath Abbey branch of Tesco (on the site, it is said, of a 12th-century castle) past, to our left, the playing fields of Dwr-y-Felin School (on the site of Roman Nidum) and Neath College, and, to our right, the old Neath river bridge (now pedestrianized); this is where the A48 used to turn off into Neath and the A465 used to start. We then dip beneath the railway and arrive finally at a pair of small roundabouts at the northern end of the modern road bridge over the River Neath.
At the second of these roundabouts the A474 heads off to the left towards Pontardawe, while the A4230 resumes, now following the original route of the A465, through Cadoxton / Llangatwg. Cadoxton-juxta-Neath, to give the village its full name in English, has far fewer shops and other commercial premises than Skewen, but again the route of the old main road is narrow for the most part.
We are paralleling a different railway now, the former Neath and Brecon (today a freight-only branch running up the Dulais Valley as far as the coal washery at Onllwyn). Immediately after this line crosses overhead from right to left of our route, we pass from the eastern end of Cadoxton into the western edge of Aberdulais and the A4230 comes to an end at a junction with the modern A465 dual carriageway – heading up the Vale of Neath towards Glynneath, Hirwaun, and the "Heads of the Valleys" road – and the A4109, which also reaches Glynneath but by means of a rather longer route through Crynant and Seven Sisters in the Dulais Valley.