Standard-gauge railway
A standard-gauge railway is a railway with a track gauge of 1,435 mm (4 ft 8 1⁄2 in). The standard gauge is also called Stephenson gauge after George Stephenson, International gauge, UIC gauge, uniform gauge, normal gauge and European gauge in the EU and Russia. It is the most widely used railway track gauge across the world with approximately 55% of the lines in the world using it. All high-speed rail lines, except those in Russia, Finland, Uzbekistan and Australia, utilise 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 approximately 4 ft 8 1⁄2 in.
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.
A popular legend that has been around since at least 1937 traces the origin of the 1435 mm (4 ft 8 1⁄2 in) gauge even further back than the coalfields of northern England, pointing to the evidence of rutted roads marked by chariot wheels dating from the Roman Empire. It is curious that the Roman pace or passus was 4.855ft or 1435mm; a thousand such was one Roman mile. Snopes categorized this legend as "false", but commented that "it is perhaps more fairly labelled as 'True, but for trivial and unremarkable reasons'". The historical tendency to place the wheels of horse-drawn vehicles approximately 5 feet (1,500 mm) apart probably derives from the width needed to fit a carthorse in between the shafts. In addition, while road-traveling vehicles are typically measured from the outermost portions of the wheel rims (and there is some evidence that the first railroads were measured in this way as well), it became apparent that for vehicles travelling on rails it was better to have the wheel flanges located inside the rails, and thus the distance measured on the inside of the wheels (and, by extension, the inside faces of the rail heads) was the important one.
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