Walnut Tree Viaduct was a railway viaduct located above the southern edge of the village of Taffs Well, South Wales. Originally built to carry the Barry Railway across a narrow gorge through which the River Taff, Taff Vale Railway and Cardiff Railway passed, it was deconstructed in 1969, leaving only two of the support columns visible from the A470 road.
Background
During the Industrial Revolution, and the mass-extraction of coal from South Wales, there was a resultant growth in construction of railways into the South Wales Coalfield. The Taff Vale Railway so monopolised the trade of shipping coal to Cardiff Docks, that mine owners were desperate for competitor railway companies to both improve speeds of shipping, provide access to new markets, and hence reduce shipping rates.
The first section of the Taff Vale Railway (TVR) to move iron from Merthyr Tydfil to Cardiff Docks opened in 1840, and included Taffs Well railway station. Following 1858, the Rhymney Railway (RR) had connected with the TVR, south of Taffs Well station at Walnut Tree Junction, a name given to the northern area of Radyr village. Almost two miles further south, Radyr station was situated, followed by Penarth Junction, later renamed Radyr Junction.
However, by 1880 the TVR and RVR were so congested with coal traffic, that a group of coal mine owners, iron makers and industrialists led by David Davies of Ocean Collieries, had all suffered from the capacity and monopoly issues created by two companies: Taff Vale Railway: which provided the dominant rail infrastructure. Capacity issues were particularly dominant after Pontypridd railway station, where down loaded trains and up return empty wagons were restricted to a single double track route, which could not be expanded due to the geographic challenges of the valley. Cardiff Docks: which having been developed by Lord Bute, were sufficient to serve his coal-exporting needs, but did not have sufficient capacity to cope with new mine developments. In light of the geographic restrictions of the valley south of Pontypridd, Davies proposed development of a secondary route which terminated at Barry, where a dock infrastructure could be developed without the mud flat or tidal restrictions which gave Cardiff's Tiger Bay its name. This would create a competitive edge to the development, and due to being later developed to a more easily accessible docks, a resultant efficiency advantage over Cardiff.
The Barry Dock and Railway Bill was introduced in the 1883 Parliamentary session but was defeated by opposition, particularly from the Bute Docks and Taff Vale Railway. The Bill was introduced again the following year and the Barry Dock and Railway Company Act was passed on 14 August 1884 for the construction of a dock between Barry and Barry Island. The name was changed to the Barry Railway Company by an Act of 5 August 1891.
Llanbradach branch
By 1889 the main line of the BRC connected Barry Docks to Hafod Junction, on the Taff Vale line, south-east of Trehafod railway station, within the Rhondda Valley. However, Davis also wanted access to the Rhymney Valley and the industrial hub of Dowlais at Merthyr Tydfil, so proposed a direct branch line to Llanbradach from Tynycaeau Junction on the Cadoxton-Trehafod main line.
Having already engineered the main line of the BRC, Chief Engineer Sir James Szlumper proposed that the new Llanbradach branch run from the BRC main line at Tynycaeau Junction near St Fagans, direct to the a junction with the Brecon and Merthyr Railway (BMR) at Llanbradach first known as Barry Junction (BMR) and later, Duffryn Isaf Junction. There would be no stations, allowing the freight trains to run unimpeded at full speed, but taking into account gradients and stopping for pinning down wagon brakes as necessary but hence maximising traffic revenue.
After passing through the Lesser Garth hill via the Walnut Tree Tunnel (), a siding served Dolomite Quarry, before the line curved right to reach the viaduct which bridged the River Taff valley via the congested geographical squeeze-point just north of Radyr, known as Walnut Tree. The height and form of the viaduct at this point not only needed to cope with the congested valley bottom, crossing the River Taff, but also at its north-eastern end, curve onto a shelf of rock on the eastern hillside followed by a deep cutting for ¼ mile. The railway then climbed the eastern hillside to finally route north-east to reach the Rhymney Railway via Penrhos Lower Junction, allowing access to Caerphilly.