Broad-gauge
Broad-gauge railways are railways which use a track gauge (distance between the rails) greater than the 1,435 mm (4 ft 8 1⁄2 in) standard gauge.
In Britain the Great Western Railway, designed by Isambard Kingdom Brunel, pioneered broad gauge in 1838 with a gauge of 7 ft 1⁄4 in (2,140 mm), and retained this gauge until 1892. Some harbours also used railways of this gauge for construction and maintenance. These included Portland Harbour and Holyhead Breakwater, which used a locomotive for working sidings. As it was not connected to the national network, this broad-gauge operation continued until the locomotive wore out in 1913. The gauge initially proposed by Brunel was 7 ft (2,134 mm) exactly but this was soon increased by 1⁄4 in (6 mm) to accommodate clearance problems identified during early testing.
While the parliament of the United Kingdom of Great Britain and Ireland was initially prepared to authorise lines built to the broad gauge of 7 ft 1⁄4 in (2,140 mm), it was eventually rejected by the Gauge Commission in favour of all railways in the British Isles being built to standard gauge of 4 ft 8 1⁄2 in (1,435 mm), this being the gauge with the greatest mileage. Ireland, using the same criteria, was allocated a different standard gauge, the Irish gauge, of 5 ft 3 in (1,600 mm) which is also used in the Australian states of South Australia and Victoria. Broad-gauge lines in Britain were gradually converted to dual gauge or standard gauge from 1864, and finally the last of Brunel's broad gauge was converted over a single weekend in 1892.
...
Wikipedia