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Merthyr Tramroad and Penydarren rail locomotive
Penydarren, Merthyr Tydfil, Wales, UK
Merthyr Tramroad and Penydarren rail locomotive
associated engineer
George Overton
Richard Trevithick
date  1799 - 1804, 1815
UK era  Georgian  |  category  Railway  |  reference  SO051067
ICE reference number  HEW 705
photo  courtesy Cyfarthfa Castle Museum & Art Gallery, Merthyr Tydfil
The Merthyr Tramroad — sometimes erroneously referred to as the Penydarren Tramroad — was one of the first tracks in the country to be fitted with metal rails instead of wooden ones. Known as a plateway, it was designed for horse-drawn wagons. However, it is also famous for the first steam engine that ran the line, Richard Trevithick's Penydarren locomotive, the world's first steam locomotive to run on rails.
Trevithick was a Cornishman and a pioneer of steam power. He was the first British person to develop mechanical transportation, though his ideas were not fully appreciated in his lifetime. His Penydarren locomotive was constructed at the Penydarren Ironworks and the name Penydarren Tramroad refers to the short length of track that connected the ironworks to the Merthyr Tramroad.
By 1800, mining centre Merthyr Tydfil was the largest town in Wales and had a population of around 7,500 people. The population was increasing as a result of the Industrial Revolution and the growing need for commodities. Of the five major ironworks in the area — Dowlais (established 1759), Plymouth (1763), Cyfarthfa (1765), Ynysfach (1769) and Penydarren (1784) — Cyfarthfa was then the largest in the world.
The Glamorganshire Canal (opened 1794) was the main transport artery for iron going south to Cardiff, but it suffered from water shortages in the many locks along its length. Also, it was managed by Richard Crawshay (1739-1810), owner of Cyfarthfa ironworks, who may have given his own barges preference.
To overcome the problems, on 18th January 1799 the owners of the Dowlais (Thomas Guest, 1748-1807), Penydarren (Samuel Homfray, 1762-1822) and Plymouth (Richard Hill, d.1818) ironworks agreed to build a tramroad between Merthyr Tydfil and Abercynon, following the valley of the River Taff. They could then use horse-drawn wagons to carry their iron instead of relying on the canal.
Guest and Homfray each held five shares in the venture, while Hill had four shares and organised the tramroad’s construction — supervised by Welsh engineer George Overton (1774-1827) between 1800 and 1802. It was 15.7km long, falling 104m to its terminus at Abercynon in the south (ST085950), with a maximum gradient of 1 in 50 near Merthyr Tydfil. The tramway passed through a tunnel (southern portal at SO058045) 2.44m high and 2.57m wide, constructed in sandstone blocks, beneath part of Plymouth Ironworks. It also crossed the river twice on timber bridges at Quaker’s Yard (HEW 799, ST090966 and ST094963).
To keep the space between the rails clear for the horses’ hooves, the tramway was built without transverse sleepers and had a track gauge of 1.435m (4ft 8.5in). The L-shaped cast iron rails each weighed 25.4kg and were 910mm long and 110mm wide, with the flanges on their inside edges. They were fixed with wrought iron spikes into 130mm long oak pegs set in the centres of stone blocks approximately 750mm square. Cast iron ‘chairs’ were installed later between the rails and the bedding stones, raising the rails up to half a metre and facilitating replacement.
In 1803, Homfray engaged Trevithick (1771-1833) to install a high pressure stationary engine at Penydarren. He had heard about the Cornishman’s experiments with locomotives and thought that one could be tested here. Crawshay did not believe that a machine could replicate the work of one horse and so he and Homfray each wagered 500 guineas (£525) on whether or not Trevithick’s engine could haul 10 ‘long tons’ (11.4 tonnes) of iron bars from Merthyr Tydfil to Abercynon and return with the five empty wagons. Hill took charge of the money and acted as referee.
The locomotive that Trevithick built at Penydarren Ironworks had a horizontal cylinder 210mm in diameter with a 1.37m stroke, working at 40 strokes per minute. This was set into the boiler above the flue. The boiler was cast iron, 1.83m long and 1.3m in diameter, with a demountable plated iron chimney 3.35m tall. It was mounted on four wheels, with a large flywheel and two gear wheels on one side. The piston rod was connected to a horizontal crosshead that, via the gears, drove the flywheel and the two running wheels on the same side.
Its first ever journey on rails was during trials on 11th February 1804, followed by a 3.2km trip pulling 11.4 tonnes of iron on 20th February. The next day the locomotive travelled from Penydarren to Abercynon in four hours and five minutes, consuming just 101.6kg of coal. It had transported 70 passengers — Crawshay among them — as well as the iron bars, making the total train weight some 25 tonnes. Trevithick asserted that the engine could pull 40 tonnes.
Some 6km into the return journey, one of the bolts between axle and boiler worked loose, letting the water out of the boiler and causing delay because the boiler had to be refilled with cold water as the hot water feed pump was not working. Though Crawshay accepted that he had lost the bet, Hill quibbled over awarding the 1,000 guineas (£1,050) to Homfray on the grounds that the engine had broken some of the tram plates by being too heavy for the rails and that the boiler had leaked. It is not known whether the wager was ever honoured — or what happened to the money.
The Cambrian newspaper (established January 1804 in Swansea) dated 25th February 1804, reported the events of 21st February — "the long expected trial of Mr. Trevithick’s new-invented steam engine … took place near this town and was found to perform with admiration, all that was expected from it by its warmest advocates. In the present instance, the novel application of steam, by means of this truly valuable machine was made use of to convey along the Tram-road ten tons long weight of bar-iron from Pendarren [sic] Ironworks, to the place where it joins the Glamorganshire Canal … the machine in the hands of the present proprietors, will be made use of in a thousand instances never yet thought of for an engine”.
Subsequently the engine was indeed put to various uses — it worked a pump in April 1804, and it continued to haul goods along the tramway until July 1804 and after which it became a stationary engine working a hammer and winding. Locomotive engines were not used on tracks again until 1825, on the more robust rails of the Stockton & Darlington Railway in County Durham.
Iron continued to be transported by horse-drawn trains — three horses would pull 25 wagons at a time on the Merthyr Tramroad. Each wagon was 2.3m long and 1.44m wide with planked sides 530mm high, originally timber and later iron plate, and fitted with cast iron wheels 760-840mm in diameter and 45mm wide.
On 16th February 1815, one of the tramroad bridges collapsed owing to timber decay and the other was in a parlous state. They were replaced by segmental elliptical masonry arches of 18.3m spans, 2.75m wide, with their decks 9.75m above the river. The arches have parallel rings 460mm deep composed of 50-75mm flat stone voussoirs. Both bridges have survived and are Grade II* listed structures.
To commemorate Trevithick’s achievements, David E. Roberts unveiled a stone plinth at Penyard Road (the site of the entrance to Penydarren Ironworks, not gone) in Gwalia Place, Pontmorlais, Merthyr Tydfil on 19th April 1934. A model of the locomotive was added to the top in 1993. The inscription reads —
A full size working replica of the Penydarren locomotive was built in 1981 by the Welsh Industrial & Maritime Museum. It is still operational.
RCAHMW_NPRN 91513, 91516
Sub-contractor (tramroad, 1800-02): James Barnes
Research: ECPK
"Richard Trevithick: Giant of Steam" by Anthony Burton, Aurum Press Ltd, London, 2000
"Steam and the Mumbles Railway" by Professor Frank Llewellyn-Jones, in Transactions of the Newcomen Society, London, 9th April 1980
"William Smith, Richard Trevithick and Samuel Homfray: Their Correspondence on Steam Engines, 1804-1806" by Joan M. Eyles, in Transactions of the Newcomen Society, London, 19th May 1971
"The Cornish Giant: The Story of Richard Trevithick, father of the steam locomotive" by L.T.C. Rolt, Lutterworth Press, London, 1960
"Trevithick and the Merthyr Tramroad" by Stanley Mercer, in Transactions of the Newcomen Society, London, 11th February 1948
"Richard Trevithick: the engineer and the man" by H.W. Dickinson and Arthur Titley, Cambridge University Press, London, 1934
"Trevithick's First Rail Locomotive" by W.W. Mason, in Transactions of the Newcomen Society, London, 27th April 1932
"Life of Richard Trevithick, with an account of his inventions" by Francis Trevithick, E. & F.N. Spon, London, 1872
reference sources   CEH W&W

Merthyr Tramroad and Penydarren rail locomotive