topic ref. 53387309
Broad gauge describes any track gauge which is greater than the global standard of 1435mm (formerly defined as 4ft 8.5in).
The Great Western Railway adopted a broad gauge in the 1830s on the advice of its engineer Isambard Kingdom Brunel. He argued that his choice of 7ft 0.25in (2140mm) provided a more stable and therefore safer ride – which was true – but too many railways in other parts of the country had already been built to standard gauge.
A Royal Commission considered the implications in 1845, and their recommendations were given legal authority by the passing of the Gauge of Railways Act 1846.
This made 4ft 8.5in the British standard, with some exceptions. The GWR continued to build broad gauge lines for a while, as permitted by the 1846 Act, but surrendered in 1863 (after Brunel’s death) by starting a programme of conversion which was finally completed west of Exeter between 20 and 23 May 1892. Before this conversion, some broad gauge lines had been fitted with an additional rail providing standard gauge, known as mixed gauge.
Different gauges still pose problems in some countries now, because through running becomes difficult or impossible. Spain is building its high speed network to standard gauge, although its domestic network (and that of Portugal) remains broad gauge (1668mm). There are differences between the states in Australia, Russia also uses a broad gauge (1520mm), and the Irish gauge is 1600mm.
Variations in tramway gauges are also known: the accepted standard is 1435mm but metre gauge (1000mm) lines exist.