The iron industries of Dowlais and Merthyr needed transport systems to take their products to market, and to bring raw materials to them.

included a general permission to build tramroads as feeders from mines within four miles of the canal: the so-called "four-mile clause",[note 1] which did much to foster mineral working in the area.

From Pont Maesmawr it ran east, immediately crossing the River Taff by a floating bridge, that is, a ferry, at the ford just below Upper Boat.

It was completed by 28 December 1843 and a connection to the Taff Vale Railway was opened on 25 April 1844, when a train of Powell's coal was taken to Cardiff.

This railway was primarily intended to reach the mineral districts close to Llantrisant, with branches to Glanmychydd (or Castellau), and Gellyrhaidd, near Hendreforgan.

These were broad gauge lines, allied to the South Wales Railway, but this proved to be a considerable disadvantage, frustrating easy access to Cardiff Docks and the ironworks of Merthyr and Dowlais.

Daniel Gooch wrote, "Our object in taking the line would be chiefly for getting a connection to our own colliery and also to get, some day, into the steam coal not yet opened out.

He said that he had acquired the Llantwit Vardre tramroad for £9,000, and was prepared to make that the core of a new railway from Llantrisant to the Taff Vale line.

[3][page needed] If a new company, the Llantrissant and Taff Vale Junction Railway,[note 3] were authorised, the TVR would contribute £10,000 to the share issue.

The provision of mixed gauge on the Mwyndy branch was much delayed by the GWR, only being ready on 5 December 1864, from which date the majority of the iron ore traffic was able to take the new route.

This would enable the Cowbridge narrow (standard) gauge trains to run through to Pontypridd over the L&TVJR and the Taff Vale Railway.

[6][page needed] The approval of the Board of Trade inspecting officer was required to open the line for passenger traffic, and there were a succession of shortcomings in the arrangements at Maesaraul and on the Cowbridge Railway.

[3][page needed] The L&TVJR had been working the trains, but did not have powers to operate over the Ely Valley line, having done so as agent for the Cowbridge company only.

It would build a new line on a north-west to south-east diagonal, from the Ely Valley Railway at Ynysmaerdy to Waterhall Junction south of Radyr.

(The Waterhall Junction was originally planned to be triangular, allowing trains to turn north and reach the lower part of the Taff Vale Railway system, but this was not built.)

Further obstructive manoeuvering frustrated early completion of the through route, and eventually it was the gauge conversion of the Great Western Railway lines that unblocked the difficulty.

The TVR wished to abandon the construction of it, but there were heavy penalty clauses in the authorising Act in this event; moreover a new colliery had been opened on the route and it was likely that the proprietor would successfully seek compensation if the line was not built.

An extension of time for construction of Railway No 1 (the Waterhall Junction line) was obtained in 1877 and the intention was to return to Parliament the following year and apply for abandonment.

"[3][page needed] Nant Mychydd extends north-westwards from Llantrisant Common, and appeared to have potential for mining coal, and in 1823 a primitive tramroad was built to convey the output to market.

The line opened by 30 August 1883,[note 7] but although business was brisk (due to the Glyn backlog) the company still lacked money for ordinary operational purposes, and a lease to the TVR was discussed.

[3][page needed] In 1892 the management of the Glyn Colliery on the Treferig branch approached the TVR, asking for a workmen's train service to be run by contract.

[3][page needed] The thinly populated terrain through which the L&TVJR line passed had gradually been built up, and pressure arose for additional stations.

[3][page needed] The west curve of the triangle at Common Branch Junction had been abolished ion the early days, never having seen much traffic.

Now the mineral trains from Glyn Colliery to Penarth and Newport required the missing link: without it they had to be routed via Llantrisant Junction at Treforest.

Chapman is ambiguous about this, page 49: "[The TVR Traffic Manager] asked that facilities be provided at Common Branch Junction to enable trains to make use of the direct route.

"[3][page needed] At the turn of the century the passenger stations on the main line were at Church Village, Llantwit and Cross Inn.

In 1903 the Taff Vale Railway experimented with what it called "motor cars"—railmotors, that is, single passenger coaches with an integrated small steam engine.

The intention was to provide a passenger service in remote areas by setting up low-cost stopping places; these were generally 40-feet long timber platforms without shelter or any other facility.

Although the grouping is generally considered to have taken place at the beginning of 1923, the necessary negotiations resulted in the Taff Vale's transfer to the new GWR effective from January 1922.

[3][page needed] The upper end of the Trefreig branch had long been dormant, and it was successively cut back to Castellau siding by 1933, and closing completely in 1935.