In rail transport, track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks.
The term derives from the metal bar, or gauge, that is used to ensure the distance between the rails is correct.
Railways also deploy two other gauges to ensure compliance with a required standard. A loading gauge is a two-dimensional profile that encompasses a cross-section of the track, a rail vehicle, and a maximum-sized load: all rail vehicles and their loads must be contained in the corresponding envelope. A structure gauge specifies the outline into which structures (bridges, platforms, lineside equipment, etc.) must not encroach.
Uses of the term The most common use of the term "track gauge" refers to the transverse distance between the inside surfaces of the two load-bearing rails of a railway track, usually measured at to below the top of the rail head to clear worn corners and allow for rail heads having sloping sides. The term derives from the "gauge", a metal bar with a precisely positioned lug at each end that track crews use to ensure the actual distance between the rails lies within tolerances of a prescribed standard; on curves, for example, the spacing is wider than normal. Deriving from the name of the bar, the distance between these rails is also referred to as the track gauge.
Choice of gauge
Early track gauges
The earliest form of railway was a wooden wagonway, along which single wagons were manhandled, almost always in or from a mine or quarry. Initially, the wagons were guided by human muscle power; subsequently, by various mechanical methods. Timber rails wore rapidly; later, flat cast-iron plates were provided to limit the wear. In some localities, the plates were made L-shaped, with the vertical part of the L guiding the wheels; this is generally referred to as a "plateway". Flanged wheels eventually became universal, and the spacing between the rails had to be compatible with that of the wagon wheels.M. J. T. Lewis (1970), Early Wooden Railways, Routledge Keegan Paul, London
As the guidance of the wagons was improved, short strings of wagons could be connected and pulled by teams of horses, and the track could be extended from the immediate vicinity of the mine or quarry, typically to a navigable waterway. The wagons were built to a consistent pattern, and the track was made to suit the needs of the horses and wagons; the gauge was the more critical factor. The Penydarren Tramroad of 1802 in South Wales, a plateway, spaced these at over the upstands.R. Cragg (1997), Civil Engineering Heritage – Wales and West Central, Thomas Telford Publishing, London, 2nd edition, England,
The Penydarren Tramroad probably made the first journey by locomotive in 1804, and it was successful for the locomotive but unsuccessful for the track: the plates were not strong enough to carry its weight. A considerable step forward was made when cast-iron edge rails were first employed; these had the major axis of the rail section oriented vertically, giving a much stronger section to resist bending forces, and the introduction of fish-belly rails further improved this.Andy Guy and Jim Rees, Early Railways 1569–1830, Shire Publications in association with the National Railway Museum, Oxford, 2011,
Edge rails required a close match between rail spacing and wheelset configuration, reinforcing the importance of the gauge. Railways were still seen as local concerns: there was no appreciation of a future connection to other lines, and the choice of track gauge remained a pragmatic decision based on local requirements and prejudices, probably determined by existing local designs of (road) vehicles.
Thus, the Monkland and Kirkintilloch Railway (1826) in the West of Scotland used ;Don Martin, The Monkland and Kirkintilloch and Associated Railways, Strathkelvin Public Libraries, Kirkintilloch, 1995, the Dundee and Newtyle Railway (1831) in the north-east of Scotland adopted ;N. Ferguson (1995), The Dundee and Newtyle Railway including the Alyth and Blairgowrie Branches, The Oakwood Press, . the Redruth and Chasewater Railway (1825) in Cornwall chose .D. B. Barton (1966), The Redruth and Chasewater Railway, 1824–1915, D. Bradford Barton Ltd, Truro, 2nd edition
The Arbroath and Forfar Railway opened in 1838 with a gauge of ,Francis Whishaw, The Railways of Great Britain and Ireland Practically Described and Illustrated, 1842, reprint 1969, David & Charles (Publishers) Limited, Newton Abbot, and the Ulster Railway of 1839 used .
"Standard" gauge appears Locomotives were being developed in the first decades of the 19th century; they took various forms, but George Stephenson developed a successful locomotive on the Killingworth Wagonway, where he worked. His designs were successful, and when the Stockton and Darlington Railway was opened in 1825, it used his locomotives, with the same gauge as the Killingworth line, .W W Tomlinson, The North Eastern Railway, its Rise and Development, Andrew Reid & Co, Newcastle upon Tyne, 1915Nicholas Wood, A Practical Treatise on Rail-Roads, Longman, Orme, Brown, Green and Longmans, London, Third edition, 1838
The Stockton and Darlington line was very successful, and when the Liverpool and Manchester Railway, the first intercity line, was opened in 1830, it used the same gauge. It too was very successful, and the gauge, widened to and named "standard gauge", was well on its way to becoming the established norm.
Gauge differences The Liverpool and Manchester was quickly followed by other trunk railways, with the Grand Junction Railway and the London and Birmingham Railway forming a huge preponderance of standard gauge. When Bristol promoters planned a line from London, they employed the innovative engineer Isambard Kingdom Brunel. He decided on a wider gauge, to give greater stability, and the Great Western Railway adopted a gauge of , later eased to . This became known as broad gauge. The Great Western Railway (GWR) was successful and was greatly expanded, directly and through friendly associated companies, widening the scope of broad gauge.
At the same time, other parts of Britain built railways to standard gauge, and British technology was exported to European countries and parts of North America, also using standard gauge. Britain was polarised into two areas: those that used broad gauge and those that used standard gauge. In this context, "standard gauge" was referred to as "narrow gauge" to emphasize the contrast. Some smaller concerns selected other non-standard gauges: the Eastern Counties Railway adopted . Most of them converted to standard gauge at an early date, but the GWR's broad gauge continued to grow.
The larger railway companies sought to expand geographically, and large areas were considered under their control. When a new independent line was proposed to open up an unconnected area, the gauge was crucial in determining the allegiance that the line would adopt: if it was broad gauge, it had to be friendly to the Great Western Railway; if narrow (standard) gauge, it had to favor the other companies. The battle to persuade or coerce that choice became very intense, and became referred to as the "gauge wars".
As passenger and freight transport between the two areas became increasingly important, the difficulty of moving from one gauge to the other—the break-of-gauge—became more prominent and more objectionable. In 1845, a Royal Commission on Railway Gauges was created to look into the growing problem, and this led to the Regulating the Gauge of Railways Act 1846, which forbade the construction of broad gauge lines unconnected with the broad gauge network. The broad-gauge network was eventually converted—a progressive process completed in 1892, known as gauge conversion. The same Act mandated the gauge of for use in Ireland.
Gauge selection in other countries
As railways were built in other countries, the gauge selection was pragmatic: the track would have to fit the rolling stock. If locomotives were imported from elsewhere, especially in the early days, the track would be built to fit them. In some cases, standard gauge was adopted, but many countries or companies chose a different gauge as their national gauge, either by governmental policy or as a matter of individual choice.The Russian Railways and Imperial Intersections in the Russian Empire, Karl E. M. Starns, Thesis, University of Washington 2012, p. 33
Terminology
Standard gauge is generally known world-wide as being . Terms such as broad gauge and narrow gauge do not have any fixed meaning beyond being materially wider or narrower than standard.
In British practice, the space between the rails of a track is colloquially referred to as the "four-foot", and the space between two tracks the "six-foot", descriptions relating to the respective dimensions.
Standard gauge
In modern usage, the term "standard gauge" refers to . The standard gauge is dominant in most countries, including those in North America, most of Western Europe, North Africa, the Middle East, and China.
Broad gauge
In modern usage, the term "broad gauge" generally refers to track spaced significantly wider than .
Broad gauge is the dominant gauge in countries in the Indian subcontinent, the former Soviet Union (CIS states, Baltic states, Georgia, and Ukraine), Mongolia, Finland (which still uses the original Russian imperial gauge of 1524mm), Spain, Portugal, Argentina, Chile, and Ireland. It is also used for the suburban railway systems in South Australia, and Victoria, Australia.
Medium gauge The term "medium gauge" had different meanings throughout history, depending on the local dominant gauge in use.
In 1840s, the Irish gauge was considered a medium gauge compared to Brunel's broad gauge and the narrow gauge, which became the modern standard gauge.
Narrow gauge
In modern usage, the term "narrow gauge" generally refers to track spaced significantly narrower than .
Narrow gauge is the dominant or second-dominant gauge in countries in Southern, Central, and East Africa; Southeast Asia; Japan; Taiwan; the Philippines; and Central and South America.
During the period known as the "battle of the gauges", Stephenson's standard gauge was commonly known as "narrow gauge", while Brunel's railways' gauge was termed "broad gauge". Many narrow gauge railways were built in mountainous regions such as Wales, the Rocky Mountains of North America, Central Europe, and South America. Industrial railways and mine railways across the world are often narrow gauge. Sugar cane and banana plantations are mostly served by narrow-gauge.
Minimum gauge
Very narrow gauges of under were used for some industrial railways in space-restricted environments such as mines or farms. The French company Decauville developed and tracks, mainly for mines; Heywood developed gauge for estate railways. The most common minimum gauges were , , , , or .
Break of gauge
Through operation between railway networks with different gauges was originally impossible; goods had to be transshipped, and passengers had to change trains. This was obviously a major obstacle to convenient transport, and in Great Britain, it led to political intervention.
On narrow-gauge lines, rollbocks or transporter wagons are used: standard-gauge wagons are carried on these special vehicles, generally with wider-rail tracks to enable the vehicles to roll on and off at transfer points.
On the Transmongolian Railway, Russia and Mongolia use while China uses the standard gauge of 1,435 mm. At the border, each carriage is lifted and its bogies are changed. The operation can take several hours for a whole train of many carriages.