Below Aberfan, the river enters a wooded section, and the remains of the Merthyr Tramroad are sandwiched between the river and the modern railway. The Merthyr or Penydarren Tramroad was built in 1793, and was the scene of the first passenger carrying train journey in the world, when Richard Trevithick's high pressure steam locomotive pulled wagons containing 5 tons of iron ore and seventy passengers in 1804. The tramway ceased operation around 1880, and this section, which is a scheduled monument, is particularly well preserved. The river is crossed by an old farm access bridge at Pont y Gwaith, with a single span of and a width of . It carries a date plaque stating it was built in 1811, but that probably refers to an earlier wooden bridge, and the main arch was rebuilt in 1993. The river turns to the east to flow around the southern edge of Treharris, and then in a large loop around higher ground on which is Goitre-Coed. Three listed bridges cross the loop. The first was built by Isambard Kingdom Brunel in 1840–41, and consists of six arches on a slight curve. It carried the single track Taff Vale Railway, but was doubled in width within 20 years, to enable it to carry twin tracks. The second was part of the Merthyr Tramroad, and was built in 1815 after the original wooden bridge collapsed into the river when a train crossed it. It has a span of and is one of the earliest railway bridges, but was in poor condition in 2002, as is the Victoria Bridge, which was also rebuilt in 1815. Continuing to the south-west, the river is crossed by the A472 and A470 roads, and at Abercynon is crossed by the B4275 road. Immediately to the south of the bridge was an aqueduct carrying the defunct Glamorganshire Canal over the river. The Afon Cynon joins on the right bank, and close to the junction is spanned by a skewed railway bridge with two arches of unequal sizes. The valley then widens, and the river begins to meander. On the northern edge of Glyncoch, the river is joined by the Nant Clydach on its right bank, and to the south of the settlement is crossed by a three-bay girder viaduct, built in 1885 to carry a branch of the Taff Vale Railway over the river to Albion Colliery at Cilfynydd. Just