The gauge of a railway is the distance between the rails. The actual gauge is not important, but the the lack of consistency of gauges has been and continues to be a big problem for railways, as it hinders the through transport of passengers and goods.
The gauge is measured between the inside edges of the head of the rail.
The gauge needs to be maintained to the specified measurement within a tolerance such as half an inch1.27 cm
0.0417 feet under to one inch2.54 cm
0.0833 feet over.
A variety of gauges are used on railways and tramways, with the most common being "standard gauge", 4'8½"1,435.099 mm. Gauges smaller than this are generally known as narrow gauge, and larger gauges as broad gauge.
Some common gauges include:
- Two feet (610 mm) and similar
Two-foot gauge is used for many mining, sugar, construction and other industrial lines, as well as many smaller general carrier railways. The first narrow-gauge railway in the world, the Ffestiniog railway uses a gauge described as 1'11⅝", which equates to 600mm.
The famous Darjeeling Himalaya railway is built to a gauge of 2'.
- Two feet, six inches (710 mm)
- Three feet (915mm)
Three-foot gauge railways are also not all that common.
- One metre (3'3⅜")
Many European branch-line railways were built to a gauge of one metre.
- Three feet, six inches (1067mm)
Three feet six inches is the smallest gauge in use for entire railway networks. The railways of Queensland, Western Australia, Tasmania, New Zealand, and various African countries including South Africa are mostly if not totally built to this gauge. Some of these railways also carry some of the heaviest traffic in the world.
- Standard gauge: four feet, eight and a half inches (1435mm)
- Russian gauge: 1520 mm
Russian gauge is the second most used in the world, connecting Russia and most of the former Soviet Union countries. It was originally a 1524 mm (5') gauge, which was retained in Finland. These gauges are close enough for Finnish trains to travel in Russia and vice versa.
- Five feet, three inches (1600mm)
Also known as the Irish gauge, this gauge is not common, but is used in Ireland, Victoria, and some other places. South Australia also adopted this gauge, but most such track has been converted to standard gauge or closed, apart from the Adelaide suburban system.
- Five feet, six inches (1677mm)
Five feet six inches is used for most main lines in India, as well as some other places. Spain and Portugal use the similar Iberian gauge, 1668 mm. The new high-speed lines in Spain use standard gauge instead, to be linked to the future European high-speed network.
- Seven feet, one quarter inch
The famous seven-foot gauge of the Great Western Railway and other railways in Britain was an early attempt at choosing a "better" gauge than what became known as standard gauge, but the fact that it was not the same gauge as most of the rest of the railways in mainland Britain led to its early demise.