Editing Track gauge

{{Short description|Spacing of the rails on a railway track}}
{{Use dmy dates|date=April 2022}}
{{more citations needed|date=December 2019}}
{{Sidebar track gauge}}
{{train topics}}

In [[rail transport]], '''track gauge''' is the distance between the two rails of a [[railway track]]. All vehicles on a rail network must have [[Wheelset (rail transport)|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 {{convert|12.7|mm|in|abbr=off|comma=off|sigfig=2}} to {{convert|15.9|mm|in|abbr=off|comma=off|sigfig=2}} below the top of the rail head in order to clear worn corners and allow for rail heads having sloping sides.<ref>{{cite book |last=Tratman |first=E.E. Russell |date=1908 |title=Railway track and track work |publisher=The Engineering News Publishing Co. |edition=3rd |location=New York |page=383}}</ref> 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.<ref>{{cite book|last= Wilson |first= John |date= 2021 |title= The train to Oodna-Woop-Woop: a social history of the Afghan Express |location= Banksia Park, South Australia |publisher= Sarlines Railway Books |isbn= 9780646842844 |page=31 }}</ref> Deriving from the name of the bar, the distance between these rails is also referred to as the track gauge.<ref>{{cite book|title=Track Maintenance Guide |author=<!--Not stated-->|date=1988 |location=Adelaide |publisher=Australian National [Railways Commission] |section=Section 12.2 }}</ref>

==Choice of gauge==

===Early track gauges===
{{See also|Permanent way (history)|Wagonway|Plateway}}

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.<ref name="lewis">M. J. T. Lewis (1970), ''Early Wooden Railways'', Routledge Keegan Paul, London</ref>

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 would be made to suit the needs of the horses and wagons: the gauge was more critical. The [[Merthyr Tramroad|Penydarren Tramroad]] of 1802 in South Wales, a plateway, spaced these at {{Track gauge|4ft4in}} over the outside of the upstands.<ref name =" cragg">R. Cragg (1997), ''Civil Engineering Heritage – Wales and West Central'', Thomas Telford Publishing, London, 2nd edition, England, {{ISBN|0 7277 2576 9}}</ref>

[[File:Chpr rail.jpg|thumb|right|Fish-belly cast-iron rails from the Cromford and High Peak Railway]]
The Penydarren Tramroad probably carried the first journey by a 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 progressive step was made when cast iron edge rails were first employed; these had the major axis of the rail section configured vertically, giving a much stronger section to resist bending forces, and this was further improved when fish-belly rails were introduced.<ref name="earlyrailways">Andy Guy and Jim Rees, ''Early Railways 1569–1830'', Shire Publications in association with the National Railway Museum, Oxford, 2011, {{ISBN|978 0 74780 811 4}}</ref>

Edge rails required a close match between rail spacing and the configuration of the wheelsets, and the importance of the gauge was reinforced. Railways were still seen as local concerns: there was no appreciation of a future connection to other lines, and the choice of track gauge was still a pragmatic decision based on local requirements and prejudices, and probably determined by existing local designs of (road) vehicles.

Thus, the [[Monkland and Kirkintilloch Railway]] (1826) in the West of Scotland used {{Track gauge|4ft6in}};<ref name = martin>Don Martin, ''The Monkland and Kirkintilloch and Associated Railways'', Strathkelvin Public Libraries, Kirkintilloch, 1995, {{ISBN|0 904966 41 0}}</ref> the [[Dundee and Newtyle Railway]] (1831) in the north-east of Scotland adopted {{Track gauge|4 ft 6 1/2 in}};<ref name = ferguson>N. Ferguson (1995), ''The Dundee and Newtyle Railway including the Alyth and Blairgowrie Branches'', The Oakwood Press, {{ISBN|0-85361-476-8}}.</ref> the [[Redruth and Chasewater Railway]] (1825) in Cornwall chose {{Track gauge|4ft}}.<ref>D. B. Barton (1966), ''The Redruth and Chasewater Railway, 1824–1915'', D. Bradford Barton Ltd, Truro, 2nd edition</ref>

The [[Arbroath and Forfar Railway]] opened in 1838 with a gauge of {{Track gauge|5ft6in}},<ref name = whishaw>[[Francis Whishaw]], ''The Railways of Great Britain and Ireland Practically Described and Illustrated'', 1842, reprint 1969, David & Charles (Publishers) Limited, Newton Abbot, {{ISBN|0-7153-4786-1}}</ref> and the [[Ulster Railway]] of 1839 used {{Track gauge|6ft2in}}.<ref name = whishaw/>

==="Standard" gauge appears===
[[File:Killingworth-locomotive.jpg|thumb|An early Stephenson locomotive]]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]], {{Track gauge|4ft8in}}.<ref name = tomlinson>W W Tomlinson, ''The North Eastern Railway, its Rise and Development'', Andrew Reid & Co, Newcastle upon Tyne, 1915</ref><ref name = wood>Nicholas Wood, ''A Practical Treatise on Rail-Roads'', Longman, Orme, Brown, Green and Longmans, London, Third edition, 1838</ref>

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 {{Track gauge|4ft8.5in|disp=or}}<ref name = tomlinson/> 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 {{Track gauge|7ft}}, later eased to {{Track gauge|7ft0.25in|lk=on}}. 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 polarised into two areas: those that used [[Brunel gauge|broad gauge]] and those that used standard gauge. In this context, standard gauge was referred to as "narrow gauge" to indicate the contrast. Some smaller concerns selected other non-standard gauges: the [[Eastern Counties Railway]] adopted {{Track gauge|5ft|lk=on}}. Most of them converted to standard gauge at an early date, but the GWR's broad gauge continued to grow.

The larger railway companies wished to expand geographically, and large areas were considered to be 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 must be friendly to the Great Western railway; if narrow (standard) gauge, it must favour the other companies. The battle to persuade or coerce that choice became very intense, and became referred to as the [[British Gauge War|"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]],<ref>{{cite web
| url = http://www.railwaysarchive.co.uk/documents/HMG_Act_Reg1846.pdf
| title =An Act for regulating the Gauge of Railways
|date = 18 October 1846
|access-date =26 April 2010}}</ref> 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, called [[Track gauge conversion|gauge conversion]]. The same Act mandated the gauge of {{Track gauge|5ft3in|lk=on}} for use in Ireland.

===Gauge selection in other countries===
[[File:World RR Gauge Map.agr.png|thumb|300px|Map of the world's railways showing the different gauges in use. {{ubl |{{legend|#a100ff|[[3 ft gauge railways|3 ft gauge]] (914 mm)}}
|{{legend|#6000ff|[[Meter gauge]] (1,000 mm)}}
|{{legend|#0500e0|[[3 ft 6 in gauge railways|Cape gauge]] (1,067 mm)}}
|{{legend|#000000|[[Standard gauge]] (1,435 mm)}}
|{{legend|#c00100|[[Russian gauge]] (1,520 mm)}}
|{{legend inline|#ff0100|[[Five foot gauge]] (1,524 mm)}}
|{{legend|#ffa000|[[Irish gauge]] (1,600 mm)}}
|{{legend|#ffc000|[[Iberian gauge]] (1,668 mm)}}
|{{legend|#ffe000|[[Indian gauge]] (1,676 mm)}}
}}
]]
[[File:Different gauges in China Railway Museum.jpg|thumb|right|upright|[[Triple gauge]], from left: {{Track gauge|1435mm}}, {{Track gauge|1000mm}}, and {{Track gauge|600mm}}, on display at the [[China Railway Museum]] in [[Beijing]]]] 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.<ref>''[https://digital.lib.washington.edu/researchworks/bitstream/handle/1773/21998/Starns_washington_0250O_10676.pdf The Russian Railways and Imperial Intersections in the Russian Empire]'', Karl E. M. Starns, Thesis, University of Washington 2012, p. 33</ref>

==Terminology==
''Standard gauge'' is generally known world-wide as being {{Track gauge|sg}}. 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 ===
{{Main|Standard-gauge railway}}
In modern usage the term "standard gauge" refers to {{Track gauge|sg}}. Standard gauge is dominant in a majority of countries, including those in North America, most of western Europe, North Africa, the Middle East, and China.

===Broad gauge===
{{Main|Broad-gauge railway}}
In modern usage, the term "broad gauge" generally refers to track spaced significantly wider than {{Track gauge|sg}}.

Broad gauge is the dominant gauge in countries in Indian subcontinent, the former Soviet Union ([[Commonwealth of Independent States|CIS]] states, Baltic states, Georgia and Ukraine), Mongolia, Finland (which still uses the original Soviet Gauge of 1524mm), Spain, Portugal, Argentina, Chile and Ireland. It is also used for the suburban railway systems in [[Railways in Adelaide|South Australia]], and [[Rail transport in Victoria|Victoria]], [[Australia]].

=== Medium gauge ===
The term "medium gauge" had different meanings throughout history, depending on the local dominant gauge in use.

In 1840s, the {{Track gauge|1600mm|lk=on}} [[Irish gauge]] was considered a medium gauge compared to Brunel's {{Track gauge|84.25in|lk=on}} [[broad gauge]] and the {{Track gauge|standard}} narrow gauge, which became the modern [[standard gauge]].<ref>{{cite web|url=http://keepontrack.scoilnet.ie/kildare/the-beginning-of-the-great-southern-and-western-railway/|title=The beginning of the Great Southern and Western Railway}}</ref>

===Narrow gauge===
{{Main|Narrow-gauge railway}}

In modern usage, the term "narrow gauge" generally refers to track spaced significantly narrower than {{Track gauge|sg}}.

Narrow gauge is the dominant or second dominant gauge in countries of Southern{{Clarify|reason=Southern what?|date=April 2025}}, Central Africa, East Africa, Southeast Asia, Japan, Taiwan, Philippines, Central America and South America,

During the period known as "[[Battle of the gauges#"The Battle of the Gauges"|the Battle of the gauges]]", Stephenson's standard gauge was commonly known as "narrow gauge", while Brunel's railway's {{Track gauge|7ft0.25in|lk=on}} 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 railway]]s and [[mine railway]]s across the world are often narrow gauge. Sugar cane and banana plantations are mostly served by narrow gauges.

===Minimum gauge===
{{Main||Minimum-gauge railway}}

[[Minimum-gauge railway|Very narrow gauges]] of under {{convert|2|ft|mm}} were used for some [[industrial railway]]s in space-restricted environments such as [[mining|mines]] or farms. The French company [[Decauville]] developed {{Track gauge|500mm}} and {{Track gauge|400mm}} tracks, mainly for mines; [[Arthur Percival Heywood|Heywood]] developed {{Track gauge|15in}} gauge for [[British narrow-gauge railways#Estate railways|estate railways]]. The most common minimum gauges were {{RailGauge|15in}},<ref name="Heywood, Minimum Gauge Railways" >{{cite book
  |last=Heywood |first=A.P.
  |author-link=Sir Arthur Heywood
  |title=Minimum Gauge Railways
  |url=https://www.gutenberg.org/ebooks/44341
  |orig-year=1881, Derby: Bemrose
  |year=1974
  |publisher=Turntable Enterprises
  |isbn=0-902844-26-1
  |ref=Heywood, Minimum Gauge Railways
}}</ref> {{RailGauge|400mm}}, {{RailGauge|16in}}, {{RailGauge|18in}}, {{RailGauge|500mm}} or {{RailGauge|20in}}.

===Break of gauge===
{{Main|Break of gauge|Variable gauge}}
[[File:Break of gauge GWR Gloucester.jpg|thumb|A cartoon depicting the horrors of goods transfer at the break of gauge at [[Gloucester railway station|Gloucester]] in 1843]]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, led to political intervention.

On narrow gauge lines, [[rollbock]]s or [[transporter wagon]]s are used: standard gauge wagons are carried on narrow gauge lines on these special vehicles, generally with rails of the wider gauge to enable those vehicles to roll on and off at transfer points.

On the [[Transmongolian Railway]], Russia and Mongolia use {{Track gauge|1520mm|lk=on}} while China uses the standard gauge of 1,435&nbsp;mm. At the border, each carriage is lifted and its [[Bogie exchange|bogies are changed]]. The operation can take several hours for a whole train of many carriages.

Other examples include crossings into or out of the former Soviet Union: Ukraine/Slovakia border on the [[Bratislava]]–[[Lviv]] train, and the Romania/Moldova border on the [[Chișinău]]–[[Bucharest]] train.<ref>{{cite web
 |url          = http://lukashenko.blogspot.com/2007/02/break-of-gauge.html
 |title        = Beyond Thunderdome: Iron Curtain 2k6
 |access-date   = 2007-10-10
 |archive-url  = https://web.archive.org/web/20110708051715/http://lukashenko.blogspot.com/2007/02/break-of-gauge.html
 |archive-date = 2011-07-08
 |url-status     = dead
}}</ref>

A system developed by [[Talgo]] and [[Construcciones y Auxiliar de Ferrocarriles]] (CAF) of Spain uses variable gauge [[wheelset (rail transport)|wheelsets]]; at the border between France and Spain, [[Through service|through passenger trains]] are drawn slowly through an apparatus that alters the gauge of the wheels, which slide laterally on the axles.<ref name="alvarez">Alberto García Álvarez, [http://www.vialibre-ffe.com/pdf/Track_gauge_changeover.pdf "Automatic Gauge Changeover for Trains in Spain"] (PDF), Fundación de los Ferrocarrilos Españoles, 2010.</ref>

A similar system is used between China and Central Asia, and between Poland and Ukraine, using the [[SUW 2000]] and [[INTERGAUGE]] variable axle systems.<ref>{{cite web |url=http://www.oevg.at/aktuell/veranstaltungen/umspurung/waryn.pdf |title=Experience and results of operation the SUW 2000 system in traffic corridors |access-date=2008-12-07 |url-status=dead |archive-url=https://web.archive.org/web/20090319042706/http://www.oevg.at/aktuell/veranstaltungen/umspurung/waryn.pdf |archive-date=2009-03-19 }}</ref> China and Poland use standard gauge, while Central Asia and Ukraine use {{Track gauge|1520mm}}.

==Dual gauge==
{{Main|Dual gauge}}
[[File:Cross-section of 4-rail dual-gauge track (standard and metre gauge).png|thumb|right|Cross-section of 4-rail dual-gauge track (standard and metre gauge/ narrow gauge) (click to enlarge)]]
[[File:Cross-section of Australian dual-gauge railway track.tif|thumb|right|Cross-section of Australian dual-gauge track – {{Track gauge|1600mm|comma=off}} and {{Track gauge|1435mm|comma=off}} gauges (click to enlarge)]]
[[File:Mixed gauge Sassari.jpg|thumb|Mixed gauge track at Sassari, Sardinia: {{Track gauge|1435mm|allk=on}} and {{Track gauge|950mm|lk=on}}]]

When individual railway companies have chosen different gauges and have needed to share a route where space on the ground is limited, [[Dual gauge|mixed gauge]] (or dual gauge) track, in which three (sometimes four) rails are supported in the same track structure, can be necessary. The most frequent need for such track was at the approaches to city terminals or at [[Break of gauge|break-of-gauge]] stations.

Tracks of multiple gauges involve considerable costs in construction (including signalling work) and complexities in track maintenance, and may require some speed restrictions. They are therefore built only when absolutely necessary. If the difference between the two gauges is large enough – for example between {{Track gauge|sg|allk=on}} and {{Track gauge|3ft6in|lk=on}} – three-rail dual-gauge is possible, but if not – for example between {{Track gauge|3ft6in}} and {{Track gauge|1000mm|allk=on}} – four rails must be used. Dual-gauge rail lines occur (or have occurred) in Argentina, Australia, Brazil, Japan, North Korea, Spain, Switzerland, Tunisia and Vietnam.

[[File:Mixed gauge track Didcot.JPG|thumb|Reconstructed [[Dual gauge|mixed-gauge]], {{Track gauge|1435mm|allk=on}} / {{Track gauge|7ft0.25in|lk=on}} track at [[Didcot Railway Museum]], England]]
On the GWR, there was an extended period between political intervention in 1846 that prevented major expansion of its {{Track gauge|7ft0.25in|lk=on}} [[broad gauge]]<ref group = note>The Act of Parliament did not prohibit expansion of the existing broad gauge system, but it had the indirect and delayed effect of forcing conformity with the "standard" gauge eventually.</ref> and the final [[Track gauge conversion|gauge conversion]] to standard gauge in 1892. During this period, many locations practicality required mixed gauge operation, and in station areas the track configuration was extremely complex. This was compounded by the common rail having to be at the platform side in stations; therefore, in many cases, standard-gauge trains needed to be switched from one side of the track to the other at the approach. A special fixed point arrangement was devised for the purpose, where the track layout was simple enough.<ref group="note">{{cite book |first1=S. C. |last1=Jenkins |name-list-style=and |first2=R. C. |last2=Langley |title=The West Cornwall Railway |publisher=The Oakwood Press |location=Usk |year=2002 |isbn=0853615896 |mode=cs2}}, gives an illustration and description on page 66.</ref>

In some cases, mixed gauge trains were operated with wagons of both gauges. For example, MacDermot<ref name = macdermot2>E. T. MacDermot (1931), ''History of the Great Western Railway'', vol. II: 1863–1921, London: Great Western Railway, p. 316</ref> wrote:

<blockquote>In November 1871 a novelty in the shape of a ''mixed-gauge'' goods train was introduced between Truro and Penzance. It was worked by a narrow-gauge engine, and behind the narrow-gauge trucks came a broad-gauge match-truck with wide buffers and sliding shackles, followed by the broad-gauge trucks. Such trains continued to run in West Cornwall until the abolition of the Broad Gauge; they had to stop or come down to walking pace at all stations where fixed points existed and the narrow portion side-stepped to right or left.</blockquote>

==Triple gauge==
{{Main|Dual gauge#Triple gauge}}
[[File:Cross-section of Australian triple-gauge track.png|thumb|left|Cross-section of triple-gauge track at [[Gladstone railway station, South Australia|Gladstone]] and [[Peterborough railway station, South Australia|Peterborough]], [[South Australia]], before [[Sydney–Perth rail corridor|gauge standardisation]]. The three gauges require the respective gaps between the outer and inner rails to be different, unlike four-rail dual gauge.]]

In rare situations, three different gauges may converge on to a rail yard and triple-gauge track is needed to meet the operational needs of the break-of-gauge station – most commonly where there is insufficient space to do otherwise. Construction and operation of triple-gauge track and its signalling, however, involves immense cost and disruption, and is undertaken when no other alternative is available.<ref>{{cite book|title=Making tracks: 46 years in Australian railways |last=Fitch |first=Ronald J. |date=1989 |location= Kenthurst NSW |publisher=Kangaroo Press |page=141 |isbn=0864172702 }}</ref>

==Nominal track gauge==
The nominal track gauge is the distance between the inner faces of the rails. In current practice, it is specified at a certain distance below the rail head as the inner faces of the rail head (the ''gauge faces'') are not necessarily vertical. Some amount of tolerance is necessarily allowed from the nominal gauge to allow for wear, etc.; this tolerance is typically greater for track limited to slower speeds, and tighter for track where higher speeds are expected (as an example, in the US the gauge is allowed to vary between {{cvt|4|ft|8|in|mm}} to {{cvt|4|ft|10|in|mm}} for track limited to {{cvt|10|mph|km/h}}, while {{cvt|70|mph|km/h}} track is allowed only {{cvt|4|ft|8|in|mm}} to {{cvt|4|ft|9+1/2|in|mm}}. Given the allowed tolerance, it is a common practice to widen the gauge slightly in curves, particularly those of shorter radius (which are inherently slower speed curves).

Rolling stock on the network must have running gear ([[Wheelset (rail transport)|wheelsets]]) that are compatible with the gauge, and therefore the gauge is a key parameter in determining interoperability, but there are many others – see below. In some cases in the earliest days of railways, the railway company saw itself as an infrastructure provider only, and independent hauliers provided wagons suited to the gauge. Colloquially the wagons might be referred to as "four-foot gauge wagons", say, if the track had a gauge of four feet. This nominal value does not equate to the flange spacing, as some freedom is allowed for.

An infrastructure manager might specify new or replacement track components at a slight variation from the nominal gauge for pragmatic reasons.

==Units==
The gauge is defined in [[imperial units]], [[metric unit]]s or [[International System of Units|SI]] units.

Imperial units were established in the United Kingdom by the [[Weights and Measures Act 1824]]. The [[United States customary units]] for length did not agree with the imperial system until 1959, when one [[international yard]] was defined as 0.9144 meters and, as derived units, 1 foot (={{frac|1|3|}}&nbsp;yd) as 0.3048 meter and 1 inch (={{frac|1|36|}}&nbsp;yd) as 25.4&nbsp;mm.

The list shows the imperial and other units that have been used for track gauge definitions:
{| class="wikitable sortable"
! Unit
! SI equivalent
! class="unsortable" | Track gauge example
|-
| [[Imperial foot]]
| {{nowrap|304.8 mm}}
| 
|-
| [[Spanish customary units|Castilian foot]]{{citation needed|date=November 2014}}
| {{nowrap|278.6 mm}}
| {{Plainlist|1= <!--comment|dummy parameter number required if list contains "="-->
* 6 Castilian feet = {{track gauge|1672mm|lk=on}}
* 2 Castilian feet {{nowrap|558 mm}} {{nowrap|(1 ft {{frac|9|31|32}} in)}}
}}
|-
| [[Portuguese customary units|Portuguese foot]]
| {{nowrap|332.8 mm}}
| 5 Portuguese feet = {{track gauge|1664mm|lk=on}}
|-
| [[Swedish units of measurement|Swedish foot]]
| {{nowrap|296.904 mm}}
| {{Plainlist|1= <!--comment|dummy parameter number required if list contains "="-->
* 3 Swedish feet = {{track gauge|891mm|lk=on}}
* 2.7 Swedish feet = {{track gauge|802mm|lk=on}}
}}
|-
| [[Obsolete German units of measurement|Prussian foot]] (Rheinfuß)
| {{nowrap|313.85 mm}}
| {{frac|2|1|2}} Prussian feet = {{track gauge|785mm|lk=on}}
|-
| [[Austrian fathom]]{{citation needed|date=May 2013}}
| {{nowrap|1520 mm}}
| {{frac|1|2}} Austrian fathom = {{track gauge|760mm|lk=on}}
|}

==Temporary way – permanent way==
{{main|Permanent way}}
[[File:East Side Access GCT cavern with work train.jpg|thumb|Narrow gauge work train in the [[East Side Access]] cavern where the Manhattan terminus of the standard gauge [[Long Island Rail Road]] was built.]]
A '''temporary way''' is the temporary track often used for construction, to be replaced by the [[permanent way]] (the structure consisting of the rails, fasteners, [[Railroad tie|sleepers/ties]] and [[Track ballast|ballast]] (or slab track), plus the underlying subgrade) when construction nears completion. In many cases narrow-gauge track is used for a temporary way because of the convenience in laying it and changing its location over unimproved ground.

In restricted spaces such as tunnels, the temporary way might be double track even though the tunnel will ultimately be single track. The [[Airport Link Company|Airport Rail Link]] in Sydney had construction trains of {{Track gauge|900mm|lk=on}} gauge, which were replaced by permanent tracks of {{Track gauge|1435mm}} gauge.

During World War I, trench warfare led to a relatively static disposition of infantry, requiring considerable logistics to bring them support staff and supplies (food, ammunition, earthworks materials, etc.). Dense light railway networks using temporary narrow gauge track sections were established by both sides for this purpose.<ref name = wolmar>Christian Wolmar, ''Engines of War: How Wars Were Won & Lost on the Railways'', Atlantic Books, London, 2010, {{ISBN|978-1848871724}}</ref>

In 1939 it was proposed to construct the western section of the [[Yunnan–Burma Railway]] using a gauge of {{Track gauge|15.25in|lk=on}}, since such tiny or "toy" gauge facilitates the [[Minimum railway curve radius|tightest of curves]] in difficult terrain.<ref>{{cite news |url=http://nla.gov.au/nla.news-article49460166 |title=TOY RAILWAY. |newspaper=[[The Northern Standard]] |location=Darwin, NT |date=8 December 1939 |access-date=5 December 2011 |page=15 |publisher=National Library of Australia}}</ref>

==Maintenance standards==
[[File:Checking the gauge at Plymouth.JPG|thumb|Track maintenance workers checking the gauge at {{stnlnk|Plymouth}}, England]]
Infrastructure owners specify permitted variances from the nominal gauge, and the required interventions when non-compliant gauge is detected. For example, the [[Federal Railroad Administration]] in the US specifies that the actual gauge of a 1,435&nbsp;mm track that is rated for a maximum of {{convert|60|mph|km/h|1|abbr=on}} must be between {{Convert|4 ft 8|in|mm|sigfig=4|abbr=on}} and {{convert|4 ft 9.5|in|mm|abbr=on}}.<ref>{{cite web|url=http://www.fra.dot.gov/downloads/safety/tss_compliance_manual_chapter_5_final_040107.pdf|title=Track Safety Standards Compliance Manual Chapter 5 Track Safety Standards Classes 1 through 5|publisher=Federal Railroad Administration|access-date=26 February 2010|url-status=dead|archive-url=https://web.archive.org/web/20080528020612/http://www.fra.dot.gov/downloads/safety/tss_compliance_manual_chapter_5_final_040107.pdf|archive-date=28 May 2008}}</ref>

==Advantages and disadvantages of different track gauges==
{{More citations needed|section|date=May 2020}}

Speed, capacity, and economy are generally objectives of rail transport, but there is often an inverse relationship between these priorities. There is a common misconception that a narrower gauge permits a tighter turning radius, but for practical purposes, there is no meaningful relationship between gauge and curvature.<ref>{{Cite book | last = Wellington | first = Arthur | title = The Economic Theory of the Location of Railways | publisher = John Wiley & Sons | date = 1910 | location = New York | pages = 751–754}}</ref><ref>{{cite journal | last =Siddall | first = William | title = Railroad Gauges and Spatial Interaction | journal = Geographical Review | volume = 59 | issue = 1 | page = 36 | publisher = American Geographical Society | date = January 1969 | jstor = 213081 | doi = 10.2307/213081| bibcode = 1969GeoRv..59...29S }}</ref>

===Construction cost===
Narrower gauge railways usually cost less to build because they are usually lighter in construction, using smaller [[railway car|cars]] and [[locomotive]]s (smaller [[loading gauge]]), as well as smaller [[bridge]]s, smaller [[tunnel]]s (smaller [[structure gauge]]).<ref>{{cite book |first=Charles Easton |last=Spooner |url=https://books.google.com/books?id=3pUpAAAAYAAJ&pg=PA71 |title=Narrow Gauge Railways |date=1879 |page=71}}</ref> Narrow gauge is thus often used in mountainous terrain, where the savings in [[civil engineering]] work can be substantial. It is also used in sparsely populated areas, with low potential demand, and for temporary railways that will be removed after short-term use, such as for construction, the logging industry, the mining industry, or large-scale construction projects, especially in confined spaces (see [[Track gauge#Temporary way – permanent way|Temporary way – permanent way]]).

For temporary railways which will be removed after short-term use, such as those used in logging, mining or large-scale construction projects, especially in confined spaces, such as when constructing the [[Channel Tunnel]], a narrow-gauge railway is substantially cheaper and easier to install and remove. Such railways have almost vanished due to the capabilities of modern [[truck]]s. In many countries, narrow-gauge railways were built as branch lines to feed traffic to standard-gauge lines due to lower construction costs. The choice was often not between a narrow- and standard-gauge railway, but between a narrow-gauge railway and none at all.

Broader gauge railways are generally more expensive to build, because they are usually heavier in construction, use larger [[railway car|cars]] and [[locomotive]]s (larger [[loading gauge]]), as well as larger [[bridge]]s, larger [[tunnel]]s (larger [[structure gauge]]). But broader gauges offer higher speed and capacity. For routes with high traffic, greater capacity may more than offset the higher initial cost of construction.

===Interchangeability===
The [[Value (economics)|value]] or [[utility]] a user derives from a [[Goods|good]] or [[Service (economics)|service]] depends on the number of users of compatible products – the "[[network effect]]" in economics. Network effects are typically positive, resulting in a given user deriving more value from a product as other users join the same network.<ref>{{Cite book|last=Shapiro, Carl.|url=https://www.worldcat.org/oclc/39210116|title=Information rules : a strategic guide to the network economy|date=1999|publisher=Harvard Business School Press|others=Varian, Hal R.|isbn=0-87584-863-X|location=Boston, Mass.|oclc=39210116}}</ref> At national levels, the network effect has resulted in commerce extending beyond regional and national boundaries. Increasingly, many governments and companies have made their railways' engineering and operational standards compatible in order to achieve interchangeability – hence faster, longer-distance train operation. A major barrier to achieving interchangeability, however, is [[path dependence]]<ref>{{cite book |last1=Liebowitz |first1= S. |last2=Margolis |first2= Stephen |title= Encyclopedia of Law and Economics |year= 2000 |isbn= 978-1-85898-984-6 |page= 981 |publisher= E. Elgar }}</ref> – in this context the persistence of an already adopted standard to which equipment, infrastructure and training has become aligned.

Since adopting a new standard is difficult and expensive, continuing with an existing standard can remain attractive, unless longer-term benefits are given appropriate weight. An example of the consequences of path dependence is the persistence in the [[United Kingdom]] – the earliest nation to develop and adopt railway technologies – of [[structure gauge]]s that are too small to allow the larger [[rolling stock]] of continental Europe to operate in the UK. The reduced cost, greater efficiency, and greater economic opportunity offered by the use of a common standard has resulted in the historical multitude of track gauges dwindling to a small number that predominate worldwide.

When interchangeability has not been achieved, freight and passengers must be transferred through time-consuming procedures requiring manual labour and substantial capital expenditure.<ref>{{cite book |url=https://books.google.com/books?id=8OVGAQAAMAAJ&pg=RA1-PA200 |title=Irish Railways including Light Railways (Vice-Regal Commission |date=1908 |volume=XLVII |page=200 |publisher=House of Commons |location=London)}}</ref> Some bulk commodities, such as [[coal]], [[ore]], and [[gravel]], can be mechanically [[Transshipment|transshipped]], but even this is time-consuming, and the equipment required for the transfer is often complex to maintain. If rail lines of different gauges coexist in a network and a [[break of gauge]] exists, it is difficult in times of peak demand to move rolling stock to where it is needed.

Sufficient rolling stock must be available to meet a narrow-gauge railway's peak demand, which might be greater in comparison to a broader-gauge network, and the surplus equipment generates no cash flow during periods of low demand. In regions where narrow-gauge lines form a small part of the rail network (as was the case on Russia's [[Sakhalin Railway]]), extra cost is involved in designing, manufacturing or importing narrow-gauge equipment.

Solutions to interchangeability problems include [[bogie exchange]]s, a [[rollbock]] system, [[dual gauge]], [[variable gauge]], or [[gauge conversion]].

== Dominant railway gauges ==
{{Further|List of track gauges}}
{{See also|List of tram systems by gauge and electrification|Rapid transit track gauge|}}

More than half of the world's railways are built to {{Track gauge|1435 mm|allk=on}}.<ref>{{cite web|url=https://transportgeography.org/wp-content/uploads/Map_Rail_Gauge.pdf |title=Major Gauges of the Global Rail Systems, in The Geography of Transportation Systems, 6th ed.|author=Jean-Paul Rodrigue|date=2024|access-date=January 16, 2025}}</ref> New railways have been built in Africa to standard gauge. Most of the narrow-gauge railways in India are being converted to the dominant, broad-gauge.<ref>{{cite web | url=https://www.livehistoryindia.com/story/eras/indian-railways | title=Indian Railways: Battle of the Gauges | date=22 April 2021 }}</ref>

{|class="wikitable sortable"
! colspan=2 | System
! colspan=4 | Installation
|-
! Gauge
! Name
! in km
! in miles
! % world
! by location
|-
|{{Track gauge|1000mm}}
| [[Metre-gauge railway]]
|{{convert|71000|km|mi|disp=table}}
|6.4%
| [[Rail transport in Argentina|Argentina]] ({{convert|11000|km|mi|abbr=on|disp=or}}), [[Rail transport in Brazil|Brazil]] ({{convert|23489|km|mi|abbr=on|disp=or}}), [[Rail transport in Bolivia|Bolivia]], northern [[Rail transport in Chile|Chile]], [[:Category:Railway lines in Greece|Greece]] ([[:Category:Metre-gauge railways in Greece|in the disused Peloponnese network]]), [[Rail transport in Spain|Spain]] ([[Renfe Feve|Feve]], [[Ferrocarrils de la Generalitat de Catalunya|FGC]], [[Euskotren Trena|Euskotren]], [[Ferrocarrils de la Generalitat Valenciana|FGV]], [[Serveis Ferroviaris de Mallorca|SFM]]), [[Rail transport in Switzerland|Switzerland]] ([[Rhaetian Railway|RhB]], [[Montreux–Oberland Bernois railway|MOB]], [[Bernese Oberland railway|BOB]], [[Matterhorn Gotthard Bahn|MGB]]), [[Rail transport in Malaysia|Malaysia]], [[Rail transport in Thailand|Thailand]], [[Rail transport in Cambodia|Cambodia]], [[Bangladesh]], [[East Africa]], [[Rail transport in Vietnam|Vietnam]] and [[Rail transport in Denmark|Denmark]]
|-
|{{Track gauge|1067mm}}
| [[3 ft 6 in gauge railways]]
|{{convert|96000|km|mi|disp=table}}
|8.6%
| Southern and Central Africa; [[Rail transport in Nigeria|Nigeria]] (most); [[Rail transport in Indonesia|Indonesia]] (Java and Sumatera); [[Rail transport in Japan|Japan]]; [[Rail transport in Taiwan|Taiwan]]; [[Rail transportation in the Philippines|Philippines]]; [[Rail transport in New Zealand|New Zealand]]; and the Australian states of [[Rail transport in Queensland|Queensland]], [[Rail transport in Western Australia|Western Australia]], [[Rail transport in Tasmania|Tasmania]] and [[Rail transport in South Australia|South Australia.]]
|-
|{{Track gauge|1435mm}}
| {{nowrap|[[Standard-gauge railway]]}}
|{{convert|678000|km|mi|disp=table}}
|60.6%
| [[Rail transport in Albania|Albania]], [[Rail transport in Argentina|Argentina]], [[Rail transport in Australia|Australia]], [[Rail transport in Austria|Austria]], [[Rail transport in Belgium|Belgium]], [[Rail transport in Bosnia and Herzegovina|Bosnia and Herzegovina]], [[Rail transport in Brazil|Brazil]] ({{convert|194|km|mi|abbr=on|disp=or}}), [[Rail transport in Bulgaria|Bulgaria]], [[Rail transport in Canada|Canada]], [[Rail transport in the People's Republic of China|China]], [[Rail transport in Croatia|Croatia]], [[Rail transport in Cuba|Cuba]], [[Rail transport in the Czech Republic|Czech Republic]], [[Rail transport in Denmark|Denmark]], [[Rail transport in Djibouti|Djibouti]], [[Rail transport in the Democratic Republic of the Congo|DR Congo]] (Kamina-Lubumbashi section, planned), [[Rail transport in Ethiopia|Ethiopia]], [[Rail transport in France|France]], [[Rail transport in Germany|Germany]], [[Rail transport in Great Britain|Great Britain]] (United Kingdom), [[Rail transport in Greece|Greece]], [[Rail transport in Hong Kong|Hong Kong]], [[Rail transport in Hungary|Hungary]], [[Rail transport in India|India]] (only used in [[Urban rail transit in India#Rapid transit|rapid transit]] and [[High-speed rail in India|High-speed rail]]), [[Rail transport in Indonesia|Indonesia]] ([[Cut Meutia (train)|Aceh rail]], [[Bali MRT]] (under construction), [[LRT Jabodetabek]], [[LRT Jakarta]], [[MRT Jakarta East - West Line Corridor]], [[High-speed rail in Indonesia]], and [[Sulawesi]]), [[Rail transport in Italy|Italy]], [[Rail transport in Israel|Israel]], [[Rail transport in Kenya|Kenya]] ([[Mombasa–Nairobi Standard Gauge Railway]]), [[Rail transport in Laos|Laos]], [[Rail transport in Liechtenstein|Liechtenstein]], [[Rail transport in Lithuania|Lithuania]] ([[Rail Baltica]]), [[Rail transport in Luxembourg|Luxembourg]], [[Rail transport in Macedonia|Macedonia]], [[Rail transport in Mauritius|Mauritius]] ([[Metro Express (Mauritius)|Metro Express]]), [[Rail transport in Mexico|Mexico]], [[Rail transport in Montenegro|Montenegro]], [[Rail transport in the Netherlands|Netherlands]], [[Rail transport in North Korea|North Korea]], [[Rail transport in Norway|Norway]], [[Rail transport in Panama|Panama]], [[Rail transport in Peru|Peru]], [[Rail transportation in the Philippines|Philippines]], [[Rail transport in Poland|Poland]], [[Rail transport in Romania|Romania]], [[Rail transport in Serbia|Serbia]], [[Singapore MRT]], [[Rail transport in Slovakia|Slovakia]], [[Rail transport in Slovenia|Slovenia]], [[Rail transport in South Korea|South Korea]], [[Rail transport in Spain|Spain]] ([[AVE]], [[Alvia]] and [[Ferrocarrils de la Generalitat de Catalunya|FGC]]), [[Rail transport in Sweden|Sweden]], [[Rail transport in Switzerland|Switzerland]],  [[Rail transport in Turkey|Turkey]], [[Rail transport in the United States|United States]], [[Rail transport in Uruguay|Uruguay]], [[Rail transport in Venezuela|Venezuela]], north [[Rail transport in Vietnam|Vietnam]]. Also private companies' lines and JR high-speed lines in [[Rail transport in Japan|Japan]]. High-speed lines in [[Rail transport in Taiwan|Taiwan]]. [[Gautrain]] commuter system in South Africa. New lines in [[Tanzania]] and [[Nigeria]].
|-
|{{Track gauge|1520mm}}
| rowspan="2" |[[5 ft and 1520 mm gauge railways]]
|{{convert|155000|km|mi|disp=table}}
|13.8%
| [[Rail transport in Armenia|Armenia]], [[Rail transport in Azerbaijan|Azerbaijan]], [[Rail transport in Belarus|Belarus]], [[Rail transport in Georgia (country)|Georgia]], [[Rail transport in Kazakhstan|Kazakhstan]], [[Rail transport in Kyrgyzstan|Kyrgyzstan]], [[Rail transport in Latvia|Latvia]], [[Rail transport in Lithuania|Lithuania]], [[Rail transport in Moldova|Moldova]], [[Rail transport in Mongolia|Mongolia]], [[Rail transport in Russia|Russia]], [[Rail transport in Tajikistan|Tajikistan]], [[Railways in Turkmenistan|Turkmenistan]], [[Rail transport in Ukraine|Ukraine]], [[Rail transport in Uzbekistan|Uzbekistan]]. <br />''(all contiguous – redefined from {{Track gauge|1524mm}})''
|-
|{{Track gauge|1524mm}}
|{{convert|7065|km|mi|disp=table}}
|
|[[Rail transport in Estonia|Estonia]],<ref>[http://www.rrdc.com/article_05_2003_evr_todays_rwys.pdf Estonian railways today] {{webarchive |url=https://web.archive.org/web/20160303171940/http://www.rrdc.com/article_05_2003_evr_todays_rwys.pdf |date=March 3, 2016 }}, p. 32</ref> [[Rail transport in Finland|Finland]]<br />''(contiguous, and generally compatible, except high speed trains, with {{Track gauge|1520mm}}''
|-
|{{Track gauge|1600mm}}
| [[5 ft 3 in gauge railways]]
|{{convert|9800|km|mi|disp=table}}
|
| [[Rail transport in the Republic of Ireland|Ireland]], [[Rail transport in Northern Ireland|Northern Ireland]] (United Kingdom) ({{convert|1800|km|mi|abbr=on|disp=or}}), and in the Australian states of [[Victoria (Australia)|Victoria]] and [[South Australia]] ({{convert|4017|km|mi|abbr=on|disp=or}}), [[track gauge in Brazil|Brazil]] ({{convert|4057|km|mi|abbr=on|disp=or}}){{When|date=September 2022}}
|-
|{{Track gauge|1668mm}}
| [[Iberian-gauge railways]]
|{{convert|16700|km|mi|disp=table}}
|1.5%
| [[Rail transport in Portugal|Portugal]], [[Rail transport in Spain|Spain]]. Sometimes referred to as ''Iberian gauge''. In Spain the Administrador de Infraestructuras Ferroviarias (ADIF) managed {{convert|11683|km|abbr=on}} of this gauge and {{convert|22|km|abbr=on}} of mixed gauge at end of 2010.<ref name = richter>Karl Arne Richter (editor), ''Europäische Bahnen '11'', Eurailpress, Hamburg, 2010, {{ISBN|978-3-7771-0413-3}}</ref> The Portuguese Rede Ferroviária Nacional (REFER) managed {{convert|2650|km|abbr=on}} of this gauge of this track at the same date.<ref name = richter/>
|-
|{{Track gauge|1676mm}}
| [[5 ft 6 in gauge railways]]
|{{convert|100000|km|mi|disp=table}}
|9.0%
| [[Rail transport in India|India]], [[Rail transport in Pakistan|Pakistan]], [[Rail transport in Bangladesh|Bangladesh]], [[Rail transport in Sri Lanka|Sri Lanka]], [[Rail transport in Argentina|Argentina]], [[Rail transport in Chile|Chile]], [[Bay Area Rapid Transit|BART]] in the United States [[San Francisco Bay Area]]
|-
|}

=== Prevalence ===
Total for each group of gauges in 2020:{{citation needed|date=September 2020}}
{| class="wikitable sortable" style="text-align:right"
! scope="col" | Gauge
! scope="col" | Installation (km)
! scope="col" class="unsortable" | Installation (mi)
! scope="col" | Percentage (2020)
! scope="col" | Percentage (2014)
|-
|Narrow gauge(s)
|{{convert|233391|km|mi|disp=table}} <!-- 2014 207,000 -->
|17.5%
|15.8%
|-
|Standard gauge
| {{convert|807616|km|mi|disp=table}} <!-- 2014 720,000 -->
|60.6%
|54.9%
|-
|Broad gauge(s)
|{{convert|290705|km|mi|disp=table}} <!-- 2014 385,067-->
|21.8%
|29.3%
|- class="sortbottom" 
|Totals
|{{convert|1331712|km|mi|disp=table}} 
|100%
|100%
|}

==Future==
Further convergence of rail gauge use seems likely, as countries seek to build inter-operable networks, and international organisations seek to build macro-regional and continental networks. Almost all new [[high-speed rail]] lines are built to standard gauge, except in Uzbekistan and Russia.

===Europe===
The [[European Union]] has set out to develop inter-operable freight and passenger rail networks across its area, and is seeking to standardise gauge, signalling and electrical power systems. EU funds have been dedicated to assist [[Lithuania]], [[Latvia]], and [[Estonia]] in the building of some key railway lines ([[Rail Baltica]]) of [[standard gauge]], and to assist Spain and Portugal in the construction of high-speed lines to connect Iberian cities to one another and to the French high-speed lines. The EU has developed plans for improved freight rail links between Spain, Portugal, and the rest of Europe.

===Trans-Asian Railway===
{{main|Trans-Asian Railway}}
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 these would encounter breaks of gauge as they cross Asia. Current plans have mechanized facilities at the breaks of gauge to move [[Intermodal container|containers]] from train to train rather than widespread gauge conversion. The Northern Corridor through Russia already operates since before year 2000, with increasing volumes China–Europe.

===The Americas===
{{Update section|date=May 2023}}
* 2008: Proposed link between [[Rail transport in Venezuela|Venezuela]] and [[Rail transport in Colombia|Colombia]]<ref>{{cite web|url=http://colombiareports.com/colombia-news/news/1066-colombia-and-venezuela-to-build-railroad.html|title=Colombia and Venezuela to build railroad|access-date=27 May 2011|archive-date=25 March 2012|archive-url=https://web.archive.org/web/20120325105831/http://colombiareports.com/colombia-news/news/1066-colombia-and-venezuela-to-build-railroad.html|url-status=dead}}</ref>{{Update inline|date=May 2023}}
* 2008: Venezuela via Brazil to Argentina – [[standard gauge]]<ref>{{cite news| url=http://news.xinhuanet.com/english/2008-08/21/content_9565433.htm| agency=Xinhua| title=Venezuela, Argentina begin construction of railway linking their capitals| work=China Daily| date=2008-08-21| access-date=2008-08-21| url-status=dead| archive-url=https://web.archive.org/web/20090304211950/http://news.xinhuanet.com/english/2008-08/21/content_9565433.htm| archive-date=2009-03-04}}</ref>{{Update inline|date=May 2023}}
* 2008: A proposed [[metre gauge]] line across Southern [[Rail transport in Paraguay|Paraguay]] to link Argentina at [[Resistencia, Chaco|Resistencia]] to Brazil at [[Cascavel]]; both those lines are {{Track gauge|1000mm|allk=on}}, and the new line would allow "bioceanic" running from the Atlantic port of [[Paranaguá]] in [[Rail transport in Brazil|Brazil]] to that of [[Antofagasta]] in [[Rail transport in Chile|Chile]] on the Pacific.{{Update inline|date=May 2023}}

===Africa===

The [[East African Railway Master Plan]] is a proposal for rebuilding and expanding railway lines connecting [[Transport in Ethiopia|Ethiopia]], [[Transport in Djibouti|Djibouti]], [[Transport in Kenya|Kenya]], [[Transport in Uganda|Uganda]], [[Transport in Rwanda|Rwanda]], [[Transport in Burundi|Burundi]], [[Transport in Tanzania|Tanzania]], [[Transport in South Sudan|South Sudan]] and beyond.<ref>{{cite web|date=29 April 2008|url=http://www.afrika.no/Detailed/16610.html|title=East Africa: Countries Move to Upgrade Railway Network|publisher=Business Daily (South Africa)|first=Zeddy|last=Sambu|access-date=13 May 2014|url-status=dead|archive-url=https://web.archive.org/web/20140514054108/http://www.afrika.no/Detailed/16610.html|archive-date=14 May 2014}}</ref> The plan is managed by infrastructure ministers from participating [[East African Community]] countries in association with transport consultation firm [[CPCS Transcom]].<ref>{{cite web|title=East Africa: EAC Railway Master Plan to Be Redesigned|access-date=13 May 2014|url=http://allafrica.com/stories/200904200007.html|date=20 April 2009|first=Gashegu |last=Muramira|publisher=[[New Times (Rwanda)]]}}</ref> Older railways are of {{Track gauge|1000mm|allk=on}} or {{Track gauge|3ft6in|lk=on}} gauge. Newly rebuilt lines will use [[standard gauge]]. Regular freight and passenger services began on the standard gauge [[Mombasa-Nairobi Standard Gauge Railway|Mombasa–Nairobi]] railway in 2017 and on the standard gauge [[Addis Ababa-Djibouti Railway|Addis Ababa–Djibouti]] railway in 2018.

Lines for iron ore to [[Kribi]] in [[Transport in Cameroon|Cameroon]] are likely to be {{Track gauge|1435mm|allk=on}} with a likely connection to the same port from the {{Track gauge|1000mm|allk=on}} Cameroon system.{{Update inline|date=May 2023}}

[[Rail transport in Nigeria|Nigeria's railways]] are mostly {{Track gauge|3ft6in|lk=on}} Cape gauge. The [[Lagos–Kano Standard Gauge Railway]] is a [[Track gauge conversion|gauge conversion]] project by the Nigerian Government to create a north–south standard gauge rail link. The first converted segment, between [[Abuja]] and [[Kaduna (city)|Kaduna]], was completed in July 2016.

The [[African Union]] has a 50-year plan to connect the capital cities and major centres by high-speed railways.

== Timeline ==
{|class="wikitable sortable"
! Gauge !! Date !! Chosen by
|-
| {{nowrap|{{Track gauge|4ft8.5in}}}} || 1825 || [[George Stephenson]]
|-
| {{Track gauge|5ft}} || 1827 || [[Horatio Allen]] for the [[South Carolina Canal and Railroad Company|South Carolina Canal and Rail Road Company]]
|-
| {{Track gauge|1ft11.5in}} || 1836 || [[Henry Archer]] for the [[Festiniog Railway]] to easily navigate mountainous terrain <br />(Britain's first steam-hauled narrow gauge passenger service in 1865) (originally horse-drawn)
|-
| {{Track gauge|7ft0.25in}} || 1838 || [[I. K. Brunel]]
|-
| {{Track gauge|5ft}} || 1842 || [[George Washington Whistler]] for the [[Moscow – Saint Petersburg Railway]] based on Southern US practice
|-
| {{Track gauge|5ft3in}} || 1846 || Chosen in Ireland as a compromise
|-
| {{Track gauge|5ft6in}} || 1853 || [[Lord Dalhousie]] for [[British India]], following recommendations of Mr. W. Simms, a consulting engineer<ref>{{cite book |last1=Chandra |first1=Satish |last2=Agarwal |first2=M.M. |date=2013 |title=Railway Engineering, Second Edition |location=India |publisher=Oxford University Press |page=32 |isbn=9780198083535}}</ref><ref>{{cite web |url=https://www.business-standard.com/article/opinion/broad-and-standard-118042000034_1.html |title=Broad and Standard |last=Debroy |first=Bibek |date=20 April 2018 |website=business-standard.com |publisher=Business Standard |access-date=9 January 2024}}</ref>
|-
| {{Track gauge|3ft6in}} || 1862 || [[Carl Pihl]] for the [[Røros Line]] in Norway to reduce costs
|-
| {{Track gauge|3ft6in}} || 1865 || [[Abraham Fitzgibbon]] for the [[Queensland Railways]] to reduce costs
|-
| {{Track gauge|3ft}} || 1870 || [[William Jackson Palmer]] for the [[Denver and Rio Grande Western Railroad|Denver & Rio Grande Railway]] to reduce costs (inspired by the [[Festiniog Railway]])
|-
| {{Track gauge|2ft}} || 1877 || [[Billerica and Bedford Railroad|George E. Mansfield]] for the [[Billerica and Bedford Railroad]] to reduce costs (inspired by the [[Festiniog Railway]])
|-
| {{Track gauge|2ft6in}} || 1887 || [[Everard Calthrop]] to reduce costs; had designs for a matching fleet of rolling stock
|}

==See also==
{{Portal|Trains}}
* [[History of rail transport]]
* [[List of track gauges]]
* [[List of tram systems by gauge and electrification]]
* [[Rail profile]]
* [[Rail terminology]]
* [[Rail transport modelling scales]]
* [[Rapid transit track gauge]]

==Notes==
{{Reflist|group = note}}

==References==
{{Reflist}}

==External links==
{{Commons category|Track gauge}}
{{Wikidata property|P1064}}
* [https://www.openrailwaymap.org/?style=gauge OpenRailwayMap]. A global track gauge map
* [http://www.trains.com/trn/default.aspx?c=a&id=234 A history of track gauge] {{Webarchive|url=https://web.archive.org/web/20081204140600/http://www.trains.com/trn/default.aspx?c=a&id=234 |date=4 December 2008 }} by George W. Hilton
* {{cite web|url=http://parovoz.com/spravka/gauges-e.html|title=Railroad Gauge Width|archive-url=https://archive.today/20120717001706/http://parovoz.com/spravka/gauges-en.php|archive-date=17 July 2012|url-status=dead}} – A list of railway gauges used or being used worldwide, including gauges that are obsolete.
* [http://www.era.eu.int/public/Interoperability/CR%20TSI%20-%205%20-%201520%20&nbsp;mm%20system.aspx European Railway Agency: 1520&nbsp;mm systems]{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }} (issues with the participation of 1520/1524&nbsp;mm gauge countries in the EU rail network)
* [http://southern.railfan.net/ties/1966/66-8/gauge.html The Days they Changed the Gauge in the U.S. South]
* [http://www.grijalvo.com/Tf_Ancho_de_via/Myth_Standard_Gauge__Mark_I.htm Juan Manuel Grijalvo – The Myth of the "Standard" Gauge]

{{Navbox track gauge}}
{{Rail tracks}}
{{Railway track layouts}}
{{Authority control}}

{{DEFAULTSORT:Rail Gauge}}
[[Category:Track gauges| ]]
[[Category:Track geometry|Gague]]