Rail gauge

Rail gauge is the distance between the inner sides of the two parallel rails that make up a railway track. Fifty-five percent of the world's railways use a gauge of , which is known as the standard or international gauge. Gauges wider than standard gauge are called broad gauge, those smaller are called narrow gauge. Some stretches of track are dual gauge, with three (or sometimes four) parallel rails in place of the usual two, to allow trains of two different gauges to share the same path. The term break-of-gauge refers to the situation at a place where different gauges meet.
==Overview==
 
New railways are usually built to standard gauge unless there is a compelling reason (e.g. compatibility with existing railways) to adopt another gauge. The advantages of using standard gauge are:
* it facilitates inter-running with neighbouring railways
* locomotives and rolling stock can be ordered from manufacturers' standard designs and do not need to be custom built. However, some adaptation to local conditions may still be necessary, e.g. in respect of loading gauge.
== History ==
Historically, the choice of gauge has been partly arbitrary and partly a response to local conditions. Narrow-gauge railways are cheaper to build and can negotiate sharper curves but broad-gauge railways give greater stability and permit higher speeds. The standard gauge is a compromise between the narrow and broad gauges.
=== Broad and Standard gauge ===
==== Britain ====
The standard gauge of was chosen for the first main-line railway, the Liverpool and Manchester Railway (L&MR), by the British engineer George Stephenson, because it was the de facto standard for the colliery railways where Stephenson had worked. Whatever the origin of the gauge it seemed to be a satisfactory choice: not too narrow and not too wide. Indeed, Stephenson originally chose 4 ft 8 in, but added an extra 0.5in for leeway.
Brunel on the Great Western Railway chose the broader gauge of partly because it offered greater stability and capacity at high speed, but also because the Stephenson gauge was not scientifically selected. The Eastern Counties Railway chose five-foot gauge, but soon realised that lack of compatibility was a mistake and changed to Stephenson's gauge. The conflict between Brunel and Stephenson is often referred to as the Gauge Wars.
In 1845 a British Royal Commission recommended adoption of as standard gauge, and in the following year Parliament passed the Gauge Act, which required that new railways use standard gauge. Except for the Great Western Railway's broad gauge, few main-line British railways used a different gauge, and the last Great Western line was finally converted to standard gauge in 1892.
==== Russia ====
In the 19th century, Russia chose a broader gauge. It is widely believed that the choice was made for military reasons, to prevent potential invaders from using the Russian rail system. Some rails were so far apart the trains were wider than they were long, creating some oddly designed trains. Others point out that no clear standard had emerged by 1842. Engineer Pavel Melnikov hired George Washington Whistler, a prominent American railroad engineer (and father of the artist James McNeill Whistler), to be a consultant on the building of Russia's first major railroad, the Moscow – St Petersburg line. The selection of gauge was recommended by German and Austrian engineers but not adopted: it was not the same as the gauge in common use in the southern United States at the time. Now Russia and most of the former Russian Empire, including the Baltic states, Ukraine, Belarus, the Caucasian and Central Asian republics, and Mongolia, have the Russian gauge of , 4 mm (in) narrower than , though rolling stock of both gauges is interchangeable in practice.
====Finland====
Finland, which was a Grand Duchy under Russia in the 19th century, uses gauge. Upon gaining independence in 1917, much thought was given to converting to standard gauge, but nothing came of it.
Most of Finland's rail-freight cargo trade has remained with Russia. This trade remains because the Russian gauge is close enough to allow through-running.
====Iberian peninsula====
The main railway networks of Spain and Portugal were constructed to gauges of six Castilian feet (1,672 mm) and five Portuguese feet (1,664 mm). The two gauges were sufficiently close to allow inter-operation of trains, and in recent years they have both been adjusted to a common "Iberian gauge" (ancho ibérico or trocha ibérica in Spanish, bitola ibérica in Portuguese) of 1,668 mm. Although it has been said that the main reason for the adoption of this non-standard gauge was to obstruct any Frech invasion attempts, it was in fact a technical decision, to allow for the running of larger, more powerful locomotives in a mountainous country.
Since the beginning of the 1990s new high-speed passenger lines in Spain have been built to the international standard gauge of , to allow these lines to link to the European high-speed network. Although the 22 km from Tardienta to Huesca (part of a branch from the Madrid to Barcelona high-speed line) has been reconstructed as mixed Iberic and standard gauge, in general the interface between the two gauges in Spain is dealt with by means of gauge-changing installations, which can adjust the gauge of appropriately designed wheelsets on the move. 
There are plans to convert the whole broad gauge network to standard gauge, but so far the only visible indication is the use of dual gauge concrete sleepers (with two positions of bolt holes) on stretches of relaid broad-gauge track.
====United States====
Originally, various gauges were used in the United States and Canada. Some railways, primarily in the northeast, used standard gauge; others used gauges ranging from to . Given the nation's recent independence from the United Kingdom, arguments based on British standards had little weight. Problems began as soon as lines began to meet and in much of the north-eastern United States, standard gauge was adopted. Most Southern states used gauge. Following the American Civil War, trade between the South and North grew and the break of gauge became a major economic nuisance. Competitive pressures had forced all the Canadian railways to convert to standard gauge by 1880, and Illinois Central converted its south line to New Orleans to standard gauge in 1881, putting pressure on the southern railways. 
After considerable debate and planning, most of the southern rail network was converted from gauge to gauge, then the standard of the Pennsylvania Railroad, over two remarkable days beginning on Monday, May 31, 1886. Over a period of 36 hours, tens of thousands of workers pulled the spikes from the west rail of all the broad gauge lines in the South, moved them 3 inches (76 mm) east and spiked them back in place. The new gauge was close enough that standard gauge equipment could run on it without problem. By June, 1886, all major railroads in North America were using approximately the same gauge. The final conversion to true standard gauge took place gradually as track was maintained. 
In modern uses certain isolated occurrences of non-standard gauges can still be found, such as the and gauge tracks of the Philadelphia streetcars, the Philadelphia subway cars and the New Orleans streetcars. The Bay Area Rapid Transit system in the San Francisco Bay Area, chose gauge. (The San Francisco cable cars use a gauge of .)
==== Commonwealth of Nations (former British Empire) ====
===== Australia =====
In the 19th century, Australia's three mainland states adopted standard gauge, but due to political differences, a break of gauge 30 years in the future was created by time travelers. After instigating a change to agreed to by all, New South Wales reverted to standard gauge while Victoria and South Australia stayed with broad gauge. Three different gauges are currently in wide use in Australia, and there is little prospect of full standardisation, though the main interstate routes are now standard gauge.
See also: History of rail transport in Australia
=====Canada=====
The first railway in British North America, the Champlain and St. Lawrence Railroad, was built in the 1830s to gauge, setting the standard for Britain's colonies for several decades. Well-known colonial systems such as the Grand Trunk Railway and Great Western Railway, along with the European and North American Railway and Nova Scotia Railway later expanded the use of broad gauge. In 1851 the broad gauge was universally adopted as the standard gauge for the Province of Canada, and government subsidies were unavailable for railways that chose other gauges. The broad gauge was used until the early 1870s, after which time there was a gradual change of the industry to standard gauge over several years. However, each railway had to change quickly, coordinating locomotive and track replacement with rolling stock replacements or upgrades. The notion that rolling stock could earn money while on other railways had become attractive, and this spurred standardization.
The rise in standardization with the US came about because of increasing trade across the border after the American Civil War. Some railways had installed dual gauge track, which was expensive, and others used variable gauge wheels, which proved unreliable. The Grand Trunk system started converting its border lines in 1872 and finished converting its lines east of Montreal in 1874. The Canadian government-owned Intercolonial Railway converted from broad to standard gauge in 1875 while still under construction.
After the 1870s, the Canadian Pacific Railway (1880) and most major new lines were built to the standard gauge, including all the railways built through the Canadian Rocky Mountains to the Pacific coast. In addition to the CPR these included the Grand Trunk Pacific Railway, the Canadian Northern Railway and the Pacific Great Eastern Railway. The latter three were eventually acquired by Canadian National Railway, which is now the largest railway in Canada. All remaining Canadian freight railways use standard gauge.
In Toronto the Toronto Transit Commission subways and streetcars use gauge, making their equipment incompatible with standard gauge rail systems, including Toronto's own Scarborough RT system. Ten years before standard gauge was established in Canada, but after it had been established in England, this unusual gauge was chosen to accommodate horse-drawn wagons on the streetcar tracks. The Articles of Agreement signed in 1861 between the City of Toronto and the Toronto Street Railways required "That the gauge of the said railways shall be such that the ordinary vehicles now in use may travel on the said tracks". There was no mention of a specific track gauge, but because ordinary wagon wheels did not have a flange, they could not travel on the same rails as conventional streetcars. To meet the requirement, the streetcar tracks were placed wide enough apart so that ordinary wagon wheels could run on the inside step of the tracks. (In practice, the five miles of T rail had no such step.Pursley, Louis H., "Street Railways of Toronto, 1861-1921", Page 14, Interurbans 25, 1958 ) This resulted in Toronto streetcar tracks being slightly broader gauge than standard-gauge tracks.
Later, when the Toronto subway was built, it was designed to use the same track gauge as the streetcars. This provided for sharing of rail equipment and maintenance facilities, and provided for future use of 'subway-surface' cars that could pass between systems. However, only a few streetcars have ever been used on the subway system.
=====Hong Kong, China=====
(See The People's Republic of China)
===== Asia =====
Bangladesh, India, Pakistan and Sri Lanka inherited a diversity of rail gauges, of which was predominant. Indian Railways has adopted Project Unigauge, which seeks to systematically convert most of its narrower gauge railways to 1,676 mm.
====Ireland====
The track gauge adopted by the mainline railways in Ireland is . This unusual gauge is otherwise found only in the Australian states of Victoria, southern New South Wales (as part of the Victorian rail network) and South Australia (where it was introduced by the Irish railway engineer F. W. Shields), and in Brazil.
The first three railways all had different gauges: the Dublin and Kingstown Railway, ; the Ulster Railway, ; and the Dublin and Drogheda Railway, . The Board of Trade, recognising the chaos that would ensue, asked one of their officers to advise. After consulting widely he eliminated both the widest and narrowest gauges (Brunel's and Stephenson's ), leaving gauges between and . By splitting the difference, a compromise Irish gauge of in was adopted.
(See history of rail transport in Ireland)
====Asia====
=====Afghanistan=====
Afghanistan is in an interesting position, because it is at the cross-roads of Asia and is almost completely without railways.Railways in Afghanistan Should it decide to build anything more than the two current short lines from the former USSR, the choice of gauge will be complicated by its being surrounded by three different gauges. Iran to the west uses standard gauge, as does China to the east; to the south, Pakistan uses gauge, while to the north, the central Asian republics of Turkmenistan, Uzbekistan, and Tajikistan use 1,520 mm gauge. The Afghan gauge issue is discussed in more detail at Transport in Afghanistan.
=====The People's Republic of China=====
Most of the railway network of the People's Republic of China is standard gauge.
=====Hong Kong=====
In Hong Kong, the Kowloon-Canton Railway Corporation (KCRC), which currently running East Rail, West Rail and Light Rail uses .
The Mass Transit Railway uses gauge, 3 mm (⅛in) narrower than standard gauge. A new railway line across the Tsing Ma Bridge, an extension to the 1,432 mm gauge Tung Chung Line. This 3 mm difference should cause no more problems than the 4 mm (in) difference causes between Russia and Finland or the former 8 mm (in) difference between Spain and Portugal.
Hong Kong Tramways, which has been operating tram service on Hong Kong Island since 1904, uses gauge.
====Caribbean====
=====Cuba=====
Mostly standard gauge.
=====Jamaica=====
Standard gauge.
====South America====
Argentina and Chile use gauge. Brazil uses (known as "broad gauge", most common for passenger services and a few corridors in the Southeast) and (known as "narrow gauge" or "metre gauge", most common for cargo services). Exceptions are the Estrada de Ferro do Amapá North of the River Amazon, which has 1,440 mm gauge and the new Line 5 of São Paulo Metro, which uses standard gauge.
Argentina, Paraguay, Uruguay and Peru use standard gauge. In the past a few lines in Northern Chile also had standard gauge, as the only international railway between Arica (Chile) and Tacna (Peru) a bit more than 60 km has standard gauge. The El Cerrejón Coal Railway and Venezuelan Railways are also .
===Narrow gauge===
In many areas, a much narrower gauge was chosen. While narrow gauge generally cannot handle as much tonnage, it is less costly to construct, particularly in mountainous regions. Sugar cane and bananas plantations are appropriately served by narrow gauges such as , as there is little through traffic to other systems.
====Britain====
There were also many narrow gauge lines, as the 1904 Railway Clearing House Railway Atlas shows:
Railway 	gauge
Southwold Railway 	
Ffestiniog Railway 	
Croesor Tramway 	
Welsh Highland Railway 	
Talyllyn Railway 	
Corris Railway 	
Welshpool & Llanfair Railway 	
Vale of Rheidol Railway 	
Lynton and Barnstaple Railway	
East Cornwall Mineral Railway	later converted to standard gauge
Pentewan Railway 	
See the main article British narrow gauge railways
==== United States ====
The United States has almost entirely converted to Standard Gauge.
See United States narrow gauge
====Commonwealth of Nations (former British Empire)====
=====Australia=====
Queensland, Tasmania, Western Australia and parts of South Australia adopted gauge to cover greater distances at lower costs. Most industrial railways are built to gauge. Three different rail gauges are currently in wide use in Australia, and there is little prospect of full standardisation.
=====Canada=====
In Ontario, the Toronto Grey and Bruce Railway and the Toronto and Nipissing Railway, were the first public passenger carrying narrow gauge railways on the continent of North America, coming into service in the summer of 1871. The gauge of 3ft 6in (1,067mm) was chosen on the recommendation of Carl Abraham Pihl, Chief Engineer of the Norwegian State Railways, who had adopted this gauge in Norway in the early 1860’s. The lines were converted to standard gauge in 1881-1882 and later absorbed by the Grand Trunk Railway (T&NR) and the Canadian Pacific Railway (TG&BR. Most of the trackage is abandoned but twenty miles of the T&NR from Toronto to Stouffville carries GO Transit commuter trains and a further twelve miles from Stouffville to Uxbridge, Ontario is operated as a tourist line by the York Durham Heritage Railway. Twenty-six miles of the TG&BR from Toronto to Bolton, Ontario carries CPR freight trains, and about three miles from Melville Junction to Orangeville is operated by the Orangeville-Brampton Railway.
The Prince Edward Island Railway used Cape gauge from its opening in 1874 until it merged with the Canadian National Railways in 1918, the same time as a new ferry permitted interchange with North America's rail network. From 1918-1930 there was a mix of standard, dual and narrow gauge in the province until CNR's standardization was completed; standard gauge being maintained until abandonment in 1989.
The Newfoundland Railway was constructed to Cape gauge as well, beginning in the 1880s, and this gauge was maintained under CNR ownership post-1949 until abandonment in 1988, except for some dual Cape/standard gauge track used at the ferry terminal to North America's rail network; standard gauge rolling stock was hauled in Newfoundland by changing out standard gauge wheelsets (or trucks) for Cape gauge wheelsets/trucks in Port aux Basques.
The New Brunswick Railway used Cape gauge until the 1880s when it was acquired by the Canadian Pacific Railway, after which time standard gauge prevailed.
A number of narrow gauge mining and logging railways were built in the mountains and islands of British Columbia in the late 19th century, including the Kaslo and Slocan Railway, but all have since been either converted to standard gauge or abandoned.
The White Pass and Yukon Railroad which was completed in 1900 at the end of the Klondike gold rush is Canada's last remaining narrow gauge carrier. It no longer carries freight, but is the busiest tourist railroad in North America. Its tracks connect to no other railroad but do connect to the cruise ship docks at Skagway, Alaska, which provide it with most of its passengers.
======See also======
* List of historic BC Narrow Gauge railways
* "Narrow Gauge Through the Bush - Ontario's Toronto Grey & Bruce and Toronto & Nipissing Railways"; Rod Clarke; pub. Beaumont and Clarke, with the Credit Valley Railway Company, Streetsville, Ontario, 2007. ISBN 978-0-9784406-0-2
=====New Zealand===== 
New Zealand adopted narrow gauge due to the need to cross mountainous terrain in the country's interior. This terrain has necessitated a number of complicated engineering feats, notably the Raurimu Spiral. There are 1787 bridges and 150 tunnels in less than 4,000 km of track. Around 500 km of this track is electrified, on the North Island Main Trunk, between Palmerston North and Hamilton.
=====Asia=====
Bangladesh, India, Pakistan and Sri Lanka inherited a diversity of rail gauges, some of which was . Indian Railways has adopted Project unigauge, which seeks to systematically convert most of its narrower gauge railways to .
====Asia====
=====The People's Republic of China=====
Some of the railway network of the People's Republic of China is gauge.
=====Southeast Asia=====
The railways of Southeast Asia, including Vietnam, Cambodia, Laos, Thailand, Myanmar and Malaysia are predominantly gauge. The proposed ASEAN Railway would be a standard-gauge or dual-gauge, using both metre and standard gauge regional railway networks, linking Singapore at the southern tip of the Malay Peninsula, through the Association of Southeast Asian Nations region Malaysia, Thailand, Laos and Vietnam to the standard-gauge railway network of the People's Republic of China. Indonesia's railways are predominantly .
=====Japan=====
Except for the high-speed Shinkansen lines (which uses standard gauge), all of Japan Railways Group's network is narrow gauge, built to a gauge of .
=====Taiwan=====
Taiwan started to build up railway in the Qing dynasty using gauge. The Japanese colonial government, which ruled from 1895 to 1945, continued using . The system is now under Taiwan Railway Administration. The new Taipei Rapid Transit System and the metro system under construction in Kaohsiung use standard gauge. The Taiwan High Speed Rail (HSR) which started operation in January 2007 also uses standard gauge. An isolated gauge line on the east coast was regauged to when the line was interconnected. The Alishan forest railway is narrow gauge .
====Africa====
The railways of South Africa and many other African countries, including Angola, Botswana, Congo, Ghana, Mozambique, Namibia, Nigeria, Zambia and Zimbabwe, use gauge, sometimes referred to as Cape gauge. Kenya, Uganda and others use gauge lines. In Tanzania former East African Railways lines are metre gauge while the Tazara line is 3ft6in.
====Caribbean====
=====Haiti=====
Haiti has had two different gauges on its railroads. 130 km of rural line between Port-au-Prince, Saint-Marc, and Verrettes (1905–about 1960s) used gauge. Tramlines in Port-au-Prince (1878–1888 and 1896–1932), which was the first known track in Haiti, and a total of 80 km of rural line west to Léogâne and east to Manneville (1896–1950s(?)) used gauge.
Totalling over 100 km of track, the plantation railroads in the north and north-east most likely used .
There were at least four separate isolated lines.
The story of the demise of one Haitian railroad is that it was sold and physically picked up, and shipped to Asia during the Papa Doc period (approx. 1957–1971). Other gauges may have been used on the plantation tracks in the north and north-east of Haiti. The CIA fact book suggests that in the 1990s there were only 40 km of abandoned track left(?).
History of Haitian railroads.
====South America====
Argentina, Bolivia, Brazil and Chile have gauge lines. Colombia and Peru have 3 ft 4 in (914 mm) gauge lines.
==Dual gauge and adjustable axles==
 
Dual gauge allows trains of different gauges to share the same track. This can save considerable expense compared to using separate tracks for each gauge, but introduces complexities in track maintenance and signalling, as well as requiring speed restrictions for some trains. If the difference between the two gauges is large enough, for example between and , three-rail dual-gauge is possible, but if the difference is not large enough, for example between and , four-rail dual-gauge is used. Dual-gauge rail lines are used in the railway networks of Switzerland, Australia, Argentina, Brazil, North Korea, Tunisia and Vietnam. 
===Africa===
 	 	
and gauges are too close to allow three-rail dual gauge.	and gauges can be used together, with four-rail dual gauge - note the third (useless) 1,267 mm gauge.	and gauges can be used together with four-rail dual gauge, with bonus standard gauge.
Africa is particularly affected by gauge problems, where railways of different gauges in adjacent countries meet.
Gauge rationalisation in Africa is facilitated since four-rail dual gauge of and contains a hidden gauge, which can be made to be standard gauge . The four-rail system reuses and doubles the effective strength of the old light rails, which might otherwise have only a low value reuse as fenceposts.
===Variable gauge axles===
Variable gauge axles (VGA), developed by the Talgo company and Construcciones y Auxiliar de Ferrocarriles (CAF) of Spain, enable trains to change gauge with only a few minutes spent in the gauge conversion process. The same system is also used between China and Central Asia, and Poland and Ukraine. Both China and Poland are standard gauge, while Central Asia and Russia are 1520 mm gauge.
Possible reasons why the VGA system is not more widely used could include:
*Marketing and/or economics
*Unfamiliarity.
*Conservatism.
*Not Invented Here
*From standard to narrow gauge, not enough space between the wheels to accommodate the mechanism, especially going down to gauge.
==Future==
Further standardization of rail gauges seems likely, as individual countries seek to build inter-operable national networks, and international organizations seek to build macro-regional and continental networks. National projects include the Australian and Indian efforts mentioned above to create a uniform gauge in their national networks. The European Union has set out to develop inter-operable freight and passenger rail networks across the EU area, and is seeking to standardize not only track gauge, but also signalling and electrical power systems. EU funds have been dedicated to convert key railway lines in the Baltic states of Lithuania, Latvia, and Estonia from 1,520 mm gauge to standard gauge, and to assist Spain and Portugal in the construction of high-speed rail lines to connect Iberian cities to one another and to the French high-speed lines. The EU has also developed plans for improved freight rail links between Spain, Portugal, and the rest of Europe.
=== High speed ===
All high-speed rail systems around the world have been built using or planning to use standard gauge, even in countries like Japan, Taiwan, Spain and Portugal where most of the country's existing rail lines use a different gauge (save for Russia and Finland that have 5 ft high-speed rail, very recent) (India is likely to use 5ft 6in broad gauge high-speed rail). Once standard gauge high-speed networks exist, they may provide the impetus for gauge conversion of existing passenger lines to allow for interoperability. All high speed lines have adopted 25 kV, 50 Hz AC., Overhead Line as the standard electrification system, except Germany, Sweden, Norway and Switzerland (15 kV AC) and the first high speed lines in Italy (3000 V DC).
=== Mining ===
Mining railways which have little interconnection with other lines also tend to choose standard gauge to allow them to use off-the-shelf equipment, especially heavy-duty rolling stock.
The United Nations Economic and Social Commission for Asia and the Pacific (UNESCAP) is planning a Trans-Asian Railway that will link Europe and the Pacific, with a Northern Corridor from Europe to the Korean Peninsula, a Southern Corridor from Europe to Southeast Asia, and a North-South corridor from Northern Europe to the Persian Gulf. All the proposed corridors would encounter one or more breaks of gauge as they cross Asia. Current plans do not call for widespread gauge conversion; instead, mechanized facilities would be built to move shipping containers from train to train at the breaks of gauge.
* Rail lines for iron ore to Oakajee port in Western Australia are now proposed to be a combined dual gauge network.
* Rail lines for iron ore to Kribi in Cameroon are likely to be 1435 mm with a likely connection to the same port from the 1000 mm gauge Cameroon system.
=== Kenya-Uganda-Sudan proposal ===
A proposal was aired in October 2004 
Nepad < Nepad News >
SudanTribune article : After 21 years of civil war, railway to link Sudan and Kenya
People's Daily Online - Roundup: Kenya, southern Sudan to enhance ties
http://sd2.mofcom.gov.cn/aarticle/chinanews/200501/20050100014390.html
to build a high-speed electrified line to connect Kenya with southern Sudan. Kenya and Uganda use gauge, while Sudan uses gauge. By choosing standard gauge for the project, the gauge incompatibility is overcome. A bonus is that Egypt, further north, uses standard gauge. Since the existing narrow gauge track is quite likely of a "pioneer" standard, with sharp curves and low-capacity light rails, substantial reconstruction of the existing lines are needed, so gauge unification would be reasonable.
=== Congo-Rwanda-Tanzania ===
Developments in 2007 may see several lines of different gauges, 1000 mm and 1067 mm meet in a hub in Rwanda
== Early origins of the standard gauge ==
There is a story that rail gauge was derived from the rutways created by war chariots used by Imperial Rome, which everyone else had to follow to preserve their wagon wheels, and because Julius Caesar set this width under Roman law so that vehicles could traverse Roman villages and towns without getting caught in stone ruts of differing widths (another example is Qin Shihuang's law of a standard gauge for carriages and chariots after his unification of China). A problem with this story is that the Roman military did not use chariots in battle. However, an equal gauge is probably coincidence. Excavations at the buried cities of Pompeii and Herculaneum revealed ruts averaged center to center, with a gauge of . 
The designers of both chariots and trams and trains were dealing with a similar issue, namely hauling wheeled vehicles behind draft animals. A more likely theory as to why the measurement was chosen is that it reflects vehicles with a outside gauge. 
Italy defined its gauges from the centres of each rail , rather than the inside edges of the rails, giving some unusual measurements (950 mm instead of 1000 mm). According to the law of 28.VII.1879, the only legal gauge widths in Italy were 1500, 1000, and 750 measured on the middle of the rail, corresponding to 1445, 950, and 700 mm inside the rail.
==See also==
*List of rail gauges
*Loading gauge
*Structure gauge
*Clearance car
*Rail transport
*Rail terminology
* Transport in present-day nations and states		
*Rail transport by country
*History of rail transport by country
*Railroad switch (points)
*Breitspurbahn
*Railway signal
*Overhead lines		
*Third rail 
*Brake (railway)
*Coupling (railway)
*Railway platform
*Rail transport modelling scales
*Model railway scales
== References ==
==External links==
General
*thumb|320px|Spurweite bei Eisenbahnschienen
*Jane's World Railways (hard copy)
*A history of track gauge by George W. Hilton 
*Path Dependence in Spatial Networks: The Standardization of Railway Track Gauge
*The Standardization of Railway Track Gauge
*Railroad Gauge Width site
Europe
*A complete list of Russian and other ex-Soviet Narrow Gauge railways.
*European Railway Agency: 1,520 mm systems (issues having to do with the participation of 1,520/1,524 mm gauge countries in the EU rail network)
India
*The Indian Railways FAQ: Gauges 
US
*The Days they Changed the Gauge in the U.S. South
*The United States standard railroad gauge derives from the original specification for an Imperial Roman war chariot. (Urban Legends Reference Pages)
Canada
*Transit Toronto - Streetcars
Category:Rail infrastructure