The Maerdy Branch was a railway branch line in South Wales. Financed and operated by the Taff Vale Railway, on amalgamation became part of the Great Western Railway in 1923. Designed and mainly operated as a coal mining freight railway, its creation and demise was wholly defined by the South Wales Coalfield.
The branch was wholly designed, being developed from integrating a series of private industrial track railways with the extension of the Taff Vale Railway from the south at Pontypridd. In 1840, the TVR bought the private Ferndale to Maerdy colliery track, and then extended to it from Porth from 1849.
Passenger operations started on the day of opening of the Mardy Colliery, serving interim stations from Porth at Ynyshir, Pontygwaith, Tylorstown, and Ferndale. Passenger traffic was neither heavy nor a major contribution to line finances, and so in 1900 the GWR introduced steam rail motors.
The last passenger train ran on 13 June 1964 under the Beeching cuts, leaving only the freight service to Mardy Colliery. As a result, the line was reduced to single track working. The line was placed into maintenance only upkeep from 1986, after the coal mined at Mardy was extracted from Tower Colliery.
The track was lifted in 1987, with the trackbed and most of the bridges left in situ. This formed the canal section of the Taff Trail cycle route.
In 2004, Rhondda Cynon Taff council came to an arrange with Network Rail to buy the trackbed from just north of Maerdy Junction to Margaret Street, Pontygwaith and convert it into a relief road for Ynyshir. Construction work started in May 2005, removing the remains of Ynyshir station, the bridges at Llanwonno road and Station street, and the replacement of the Rhondda Fach bridge at Ynyshir and the Ynyshir road bridge. Today the A4223 Porth and Lower Rhondda Fach Relief Road (Porth Bypass), has meant a significant decrease in traffic flows through the main street, Ynyshir Road.
- "Rhondda Valley Branches". RailBrit. Retrieved 24 December 2010.
- "TVR Maerdy Branch". Cardiff Rail. Retrieved 24 December 2010.