The Loughor viaduct was constructed to carry the broad gauge South Wales Railway (SWR) west of Swansea to Carmarthen. It was opened to traffic (broad gauge and standard gauge) in 1852. The viaduct was rebuilt several times; modifications made include the removal of its swing bridge and broad gauge tracks, replacement of the timber deck with an iron structure, and additional piles. In 1986, due to structural concerns, the track was singled and speed restrictions were imposed adding to journey times.