Standard-gauge

The standard gauge (also Stephenson gauge after George Stephenson, International gauge, or normal gauge) is a widely used railway track gauge. Approximately 55% of the lines in the world are this gauge. All high-speed rail lines, except those in Russia, Uzbekistan, and Finland, are standard gauge. The distance between the inside edges of the rails is defined to be 1435 mm except in the United States, where it is still defined in Imperial and US customary units as 4 feet 8 ¹⁄₂ inches (1,435.1 mm). It is also called the UIC gauge or UIC track gauge, the European gauge in the EU and Russia, or uniform gauge in Queensland, Australia.

As railways developed and expanded, one of the key issues was the track gauge (the distance, or width, between the inner sides of the rails) to be used. The result was the adoption throughout a large part of the world of a "standard gauge" of 1435 mm (4 ft  8 ¹⁄₂ in), allowing inter-connectivity and inter-operability.

In North East England, some early lines in colliery (coal mining) areas were 4 ft 8 in (1,422 mm), whilst in Scotland some early lines were 4 ft 6 in (1,372 mm). All these lines had been widened to standard gauge by 1846. Parts of the United States, mainly in the Northeast, adopted the same gauge, because some early trains were purchased from Britain. However, until well into the second half of the 19th century, Britain and the USA used several different track gauges. The American gauges converged as the advantages of equipment interchange became increasingly apparent; notably, the South's 5 ft (1,524 mm) broad gauge was converted to be compatible with standard gauge over the course of two days beginning on 31 May 1886.See Track gauge in the United States.

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