Passengers on the Glasgow subway, SPT underground railway, city centre train / railway, Strathclyde, Scotland, UK

The Glasgow Subway is an underground metro line in Glasgow, Scotland. Opened on 14 December 1896, it is the third-oldest underground metro system in the world after the London Underground and the Budapest Metro. It is the only heavy rail underground metro system in the United Kingdom outside London, and also the only one in the United Kingdom which operates completely underground. It is also one of the very few railways in the world with a track running gauge of 4 ft (1, 219 mm). Formerly a cable railway, the Subway was later electrified, but its twin circular lines were never expanded. The line was originally known as the Glasgow District Subway, but was later renamed Glasgow Subway Railway. It was so called when taken over by the Glasgow Corporation who renamed it the Glasgow Underground in 1936. Despite this rebranding, many Glaswegians continued to refer to the network as "the Subway". In 2003 the name "Subway" was officially readopted by its operator, the Strathclyde Partnership for Transport (SPT). A £40, 000 study examining the feasibility of an expansion into the city’s south side is in progress. The system is not the oldest underground railway in Glasgow; that distinction belongs to a 3.1 mi (5.0 km) section of the Glasgow City and District Railway opened in 1863, now part of the North Clyde Line of the suburban railway network, which runs in a sub-surface tunnel under the city centre between High Street and west of Charing Cross. Another major section of underground suburban railway line in Glasgow is the Argyle Line, which was formerly part of the Glasgow Central Railway. The Subway runs from 06:30 to 23:40 Monday to Saturday and 10:00 to 18:12 on Sunday.