Llantrisant and Taff Vale Junction Railway
In time the Canal became overwhelmed by the volume of traffic, and encouraged by the successful opening of railways with more advanced technology than the horse tramways of previous years, the Taff Vale Railway was promoted. It was authorised by Parliament in 1836 and it opened between Merthyr and Cardiff docks in 1841. The line passed close to the Maesmawr workings but did not make a connection.
Newport, Abergavenny and Hereford Railway
The South Wales valleys may be considered to run broadly southwards and many of them were already served by a railway line running to the ports. The Taff Vale Extension line was to run from east to west; this would enable it to connect into many of the valley lines, but as it crossed the grain of the valleys, it would be challenging to construct. In 1853 work was started on the Crumlin Viaduct, stated to be the largest viaduct in the world, crossing the Ebbw Valley at a height of 200 feet, and 1650 feet in length. The first section of the Taff Vale Extension line from Pontypool Road to Crumlin Junction was opened on 20 August 1855. It was a single line of Barlow rails at first, but was doubled soon afterwards. The branch down to Llanhilleth was opened to an NA&HR goods depot there on 3 September 1855 and a connection joining the Monmouthshire Railway's Western Valley line at Llanhilleth opened on 20 October 1855. Crumlin Viaduct was finished in May 1857 and was opened for traffic on 1 June 1857, together with a further three miles of single line to Tredegar Junction (now Pontllanfraith) on the Sirhowy Railway. The Sirhowy Railway had not yet been converted to a standard gauge railway, and it was not until 1865, when this was done, that the junction was used for through running.