Rail gauge
Rail gauge is the distance between two rails of a railroad. Sixty percent of the world's railways use a 4 feet 8½ in (1435 mm) gauge, which is known as standard gauge or international gauge. The place where two different gauges meet is called a break of gauge.
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 in standard. In 1845 a royal commission recommended adoption of the 4 feet 8½ in 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. Some, primarily in the north-east, used the British standard gauge; others did not, including track gauges up to six feet 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 eastern United States the standard gauge was eventually adopted. Most Southern states used a five-foot gauge. The American Civil War eventually decided the gauge question; the South's railroads were so destroyed that they had to be essentially rebuilt from scratch, and unsurprisingly the de facto Northern standard became the American standard.
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. Russia and most of the former Russian Empire, including the Baltic states, Finland, Ukraine, Belarus, the Caucasian and Central Asian republics, and Mongolia, have a wider gauge of 5 feet (1524 mm; although the official Russian measurement is 1520 mm, they are interchangeable in practice).
Spain and Portugal both use a nominal 5 feet 5.5 in gauge. The official Spanish standard is 1674 mm, and the Portuguese standard is 1665 mm. Interchange of traffic is possible with carefully designed equipment. With the advent of the European Community, Spain has embarked upon a partial regauging program. Spain's AVE high-speed rail lines, including the line from Madrid to Seville that opened in 1991 and the line from Madrid to Barcelona currently under construction, use standard gauge.
In the nineteenth century, Australia's states adopted their own railway standards, and while most states chose standard gauge, Victoria and South Australia adopted a 5 feet 3 in (1600 mm) gauge. Ireland and Northern Ireland also use the 1600 mm gauge.
In Toronto, Canada the Toronto Transit Commission subways and streetcars use a different gauge of 4 feet 10 7/8 in (1495.42 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 in (1676 mm) gauge.
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 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 built 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" ÃÂÃÂ 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 can't handle as much tonnage, it is less costly to construct, particularly in mountainous regions.
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 in (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.
A dual gauge track has three or four rails positioned such that trains of two gauges can use it; it is applied in part of the railroads of Switzerland, Australia, Brazil, North Korea, Tunisia and Vietnam.
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.
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 in (1447.8 mm) center to center, with a gauge of 4 feet 6 in (1371.6 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 in measurement was chosen is that it reflects vehicles with a 5 feet outside gauge.