Rail gauge is the distance between two rails of a railroad. Sixty percent of the world's railways use a 4 feet 8½ inch (1435 mm) gauge, which is known as standard gauge or international gauge. Rail gauges larger than standard gauge are called broad gauge, and rail gauges smaller than standard are called narrow gauge. A dual gauge railway has three or four rails positioned so that trains of two different gauges can use it. A place where different gauges meet is called a break of gauge.
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Standard gauge was developed by British engineer George Stephenson, designer of the Stockton and Darlington Railway, who convinced manufacturers to build equipment using the 4 feet 8½ inch (1435 mm) standard. In 1845 a royal commission recommended adoption of the 4 feet 8½ inch (1435 mm) standard, and 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 Great Western was converted to standard gauge in 1892.
Originally a variety of gauges were used in the United States and Canada. Some, primarily in the north-east, used the British standard gauge; others did not, including track gauges up to six feet (1829 mm) across. Given the nation's recent independence from the United Kingdom, arguments based on British standards had little weight. Problems began as soon as railroads began to meet other railroads, and in much of the north-eastern United States the standard gauge was eventually adopted. Most Southern states used a 5 ft (1524 mm) gauge. Following the American Civil War, trade between the South and North grew and the break of gauge became a major economic nuisance. After considerable debate and planning, most of the southern rail network was converted from five-foot (1524 mm) gauge to 4 foot 9 inch (1448 mm) gauge, then the standard of the Pennsylvania Railroad) over two days beginning May 31, 1886. The final conversion to standard gauge took place gradually as track was maintained.
In the nineteenth century, Russia chose a broader gauge. It is widely believed that the choice was made for military reasons, to prevent potential invaders using their rail system. Others point out that no clear standard had emerged by 1842, when Engineer 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 a 1.5 metre gauge was recommended by German and Austrian engineers, it was not the same as the five foot (1524 mm) gauge which was in common use in the Southern United States at the time. Russia and most of the former Russian Empire, including the Baltic states, Finland, Ukraine, Belarus, the Caucasian and Central Asian republics, and Mongolia, have the official Russian measurement of 1520 mm, this is 4 mm narrower than five feet (1524 mm), though rolling stock of both gauges may be interchangeable in practice).
The main railway networks of Spain and Portugal were originally constructed to gauges of six Castilian feet and five Portuguese feet. Later, following adoption of the metric system, these two gauges were defined as 1674 mm (5 ft 5.9 in) and 1665 mm (5 ft 5.55 in) respectively. The gauges were sufficiently close to allow inter-operation of trains between the two countries, and in recent years both have been adjusted to a common Iberic gauge of 1668 mm. Since the beginning of the 1990s, however, new high-speed passenger lines in Spain have been built to the international standard gauge of 1435 mm, since it is intended that these lines will eventually cross the French border and 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) have been reconstructed as mixed Iberic- and European-gauge (i.e. with three rails per track), 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 rolling stock on the move.
In the nineteenth century, Australia's then three mainland states originally adopted a uniform railway gauge of 4 foot 8½ inches (1435 mm), but due to political differences a break of gauge 30 years in the future was created. After instigating a change to 5 foot 3 inch (1600 mm) agreed to by all, New South Wales reverted back to 4 foot 8½ inches (1435 mm) while Victoria and South Australia stayed with 5 feet 3 inch (1600 mm) gauge. Ireland and Northern Ireland also use the 1600 mm gauge. Queensland, Tasmania, Western Australia and parts of South Australia adopted the supposedly cheaper narrow gauge 3 feet 6 inches (1067mm).
In Toronto, Canada the Toronto Transit Commission subways and streetcars use a different gauge of 4 feet 10 7/8 inch (1495 mm), making their equipment incompatible with all other city transit systems. The Bay Area Rapid Transit system in the San Francisco Bay Area uses 5 feet 6 inch (1676 mm) gauge.
In Hong Kong, the MTR uses a gauge of 1432 mm, which is 3 mm narrower than the standard gauge. The trains might be running on standard gauge slowly, but cannot operate at normal speed. If the railway is to be built the Hong Kong-Zhuhai-Macau Bridge, an extention to the Tung Chung Line (1432 mm) would perhaps be an option, but the problem of the 3 mm difference would have to be solved.
Upon independence from Britain, India, Pakistan, Bangladesh and Sri Lanka had inherited a diversity of rail gauges, of which 1676 mm was predominant. Indian Railways has adopted Project unigauge, which seeks to systematically convert most of Indian Railways' narrower gauge railways to the 1676 mm standard. Argentina and Chile also have some 1676 mm lines.
Afghanistan is in an interesting position, writing in 2004, because they are at the crossroads of Asia and are virtually without railways. Should they decide to build any, the choice of gauge will be complicated by their being surrounded by three different gauges (1435 mm, 1520 mm, 1676 mm) in four "gauge oceans" ? Iran to the west uses standard gauge, as does China to the east; to the south, Pakistan uses the 1676 mm gauge, while to the north, the central Asian republics of Turkmenia, Uzbekistan, and Tajikistan use the 1520 mm 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. Plantations such as for sugar cane and bananas are appropriately served by narrow gauge lines such as 2 foot 0 inch (610 mm), as there is little through traffic to any broader gauge main line systems.
The railways of Southeast Asia, including Vietnam, Cambodia, Laos, Thailand, Myanmar, and Malaysia are predominantly metre gauge (1000 mm). The proposed ASEAN railway, would be a standard-gauge or dual-gauge (metre and standard gauge) regional railway network, linking Singapore, at the southern tip of the Malay Peninsula, through Malaysia, Thailand, Laos, and Vietnam, to China's standard-gauge railway network.
Japan's railways are built to a 3 feet 6 inch (1067 mm) gauge. Japan's high-speed Shinkansen, or bullet trains were built to the 1435 mm standard for greater stability, which has caused some difficulties integrating high-speed and conventional passenger railway services. Taiwan, which was ruled by Japan from 1895 to 1945, has several 1067 mm lines, although its HSR high-speed line will also be standard-gauge. The railways of South Africa and many other African countries, including Angola, Botswana, Congo, Ghana, Mozambique, Namibia, Nigeria, Zambia, and Zimbabwe, use 1067 mm gauge, which is sometimes referred to as Cape gauge. Indonesia's railways are predominantly 1067 mm.
Dual gauge and adjustable axles
Dual gauge allows tracks of say broad and narrow gauge trains to share the same right of way which can be a considerable cost saving compared to having separate broad and narrow tracks. There can be difficulties and speed restrictions. If the difference between the two gauges is enough, a three rail dual gauge is possible (say 1435 mm and 1067 mm), but if the difference is not enough, a four rail dual gauge is necessary (say 1067 mm and 1000 mm). Dual gauge helps the conversion from one gauge to another. Dual gauge rail lines are used in sections of the railway networks of Switzerland, Australia, Brazil, North Korea, Tunisia and Vietnam.
Variable Gauge Axles developed by the Talgo company in Spain enable trains to travel from broad to standard gauge with only a few minutes spent in the gauge conversion process. The same system is also used between China (1435 mm) and Central Asia (1524 mm). It is not known why the VGA system is not more widely used, particularly between standard and narrow gauges.
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 even 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 signaling and electrical power systems. EU funds have been dedicated to convert key railway lines in the Baltic states of Lithuania, Latvia, and Estonia from the 1520 mm gauge to standard gauge, and to assist Spain and Portugal in the construction of additional 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.
All of the high-speed rail systems around the world have been built using or are 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. Once standard gauge high-speed networks exist, they may provide the impetus for gauge conversion of existing passenger lines to allow for interoperability.
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 of 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.
A proposal was aired in October 2004 to built a high speed electrified line to connect Kenya with southern Sudan. Kenya and Uganda have 1000mm gauge, while Sudan is 1067mm, however by choosing 1435mm for the project, the gauge incompatibility is overcome. A bonus would be that 1435mm gauge matches that used by Egypt further north. 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 line is probably needed anyhow. May as well unify the gauge at the same time.
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. However, an equal gauge is probably coincidence. Excavations at the buried cities of Pompeii and Herculaneum revealed ruts averaged 4 feet 9 inch (1448 mm) center to center, with a gauge of 4 feet 6 inch (1372 mm). 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 why the 4 feet 8½ inch (1435 mm) measurement was chosen is that it reflects vehicles with a 5 feet (1524 mm) outside gauge.
- Ambrussum has some exant Roman chariot tracks.
- Loading gauge
- Broad gauge
- Dual gauge
- Narrow gauge
- Rail transport
- Rail terminology
- Rail transport by country
- History of rail transport by country