Rail gauge



Track gauge or rail gauge is the distance between the inner sides of the heads of the two load bearing rails that make up a single railway line. Sixty percent of the world's railways use a standard gauge of 1,435 mm (4 ft 8½ in). Wider gauges are called broad gauge; smaller gauges, narrow gauge. Break-of-gauge refers to the meeting of different gauges. Some stretches of track are dual gauge, with three or four rails, allowing trains of different gauges to share them. Gauge conversion can resolve break-of-gauge problems. An exception of a railway with no gauge is monorail where there is only one supporting rail. Some electrified railways use non load bearing third rail and occasionally a fourth rail. These additional rails are positioned between or outside the “running rails” to feed and return electrical current; they do not define the rail gauge.

Gauge tolerances specify how much the actual gauge may vary from the nominal gauge. For example, the U.S. Federal Railroad Administration specifies that the actual gauge of track that is rated for a maximum of 60 mph must be between 4 ft 8 in (1,422 mm) and 4 ft 9½ in (1,460 mm).

A track gauge is also the measuring device used to test whether rails are within the correct gauge.

History
Historically, the choice of gauge was 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.

Sometimes railway companies chose their own gauge, such as the Great Western Railway choosing.

Other times, statutes required railways to use a particular gauge, such as the Thomasville, Tallahassee and Gulf Railroad having to use standard gauge.

Early origins of the standard gauge
There is an urban legend that Julius Caesar specified a legal width for chariots at the width of standard gauge, causing road ruts at that width, so all later wagons had to have the same width or else risk having one set of wheels suddenly fall into one deep rut but not the other.

In fact, the origins of the standard gauge considerably pre-date the Roman Empire, and may even pre-date the invention of the wheel. The width of prehistoric vehicles was determined by a number of interacting factors which gave rise to a fairly standard vehicle width of a little under 2 m. These factors have changed little over the millennia, and are still reflected in today's motor vehicles. Road rutting was common in early roads, even with stone pavements. The initial impetus for the ruts probably came from the grooves made by sleds and slide cars dragged over the surfaces of ancient trackways. Since early carts had no steering and no brakes, negotiating hills and curves was dangerous, and cutting ruts into the stone helped them negotiate the hazardous parts of the roads.

Neolithic wheeled carts found in Europe had gauges varying from 1.30 to 1.75 m. By the Bronze age, wheel gauges appeared to have stabilized between 1.40 to 1.45 m which was attributed to a tradition in ancient technology which was perpetuated throughout European history. The ancient Assyrians, Babylonians, Persians and Greeks constructed roads with artificial wheelruts cut in rock spaced the wheelspan of an ordinary carriage. Such ancient stone rutways connected major cities with sacred sites, such as Athens to Eleusis, Sparta to Ayklia, or Elis to Olympia. The gauge of these stone grooves was 1.38 to 1.44 m. The largest number of preserved stone trackways, over 150, are found on Malta.

Some of these ancient stone rutways were very ambitious. Around 600 BC the citizens of ancient Corinth constructed the Diolkos, which some consider the world's first railway, a hard poros limestone road with grooved tracks along which large wooden flatbed cars carrying ships and their cargo were pulled by slaves or draft animals. The grooves were at 1.67 m centres.

The Roman Empire actually made less use of stone trackways than the prior Greek civilization because the Roman roads were much better than those of previous civilizations. However, there is evidence that the Romans used a more or less consistent wheel gauge adopted from the Greeks throughout Europe, and brought it to England with the Roman conquest of Britain in AD 43. After the Roman departure from Britain, this more-or-less standard gauge continued in use, so the wheel gauge of animal drawn vehicles in 19th century Britain was 1.4 to 1.5 m. In 1814 George Stephenson copied the gauge of British coal wagons in his area (about 1.42 m) for his new locomotive, and for technical reasons widened it slightly to achieve the modern railway standard gauge of 4 ft.

Standard gauge
What became 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; the de facto standard for the colliery railways where Stephenson had worked was. Whatever the origin of the gauge, it seemed to be a satisfactory choice: not too narrow and not too wide.

Isambard Kingdom Brunel, engineer of the Great Western Railway, chose the broader gauge of because it offered greater stability and capacity at high speed. Brunel's first locomotives were exactly 7 foot gauge and had no slack, hence the extra quarter inch. The Eastern Counties Railway chose 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 War. Several non-interconnecting lines in Scotland were but were changed to standard gauge for compatibility reasons.

In 1845 a British Royal Commission recommended adoption of as standard gauge in Great Britain,  in Ireland. The following year the Parliament of the United Kingdom passed the Gauge Act, which required that new railways use the standard gauge. Except for the Great Western Railway's broad gauge, few main-line railways in Great Britain used a different gauge. The last Great Western line was converted to standard gauge in 1892.



Broad gauge
Broad gauge refers to any gauge wider than standard gauge or. Russian, Indian, Irish, and Iberian gauges are all broad gauges. Broad gauge railways are also common for cranes in docks for short distances. Broad gauge is used to provide better stability or to prevent the easy transfer of rolling stock from railroads of other countries for political or military reasons.

Narrow gauge
In many areas narrow gauge railways have been built. As the gauge of a railway is reduced the costs of construction can also be reduced since narrow gauges allow a smaller radius curves allowing obstacles to be avoided rather than having to be built over or through (valleys and hills); the reduced cost is particularly noticeable in mountainous regions. For example, many narrow gauge railways were built in Wales and the Rocky Mountains of North America. The disadvantage of tight turns and steep gradients is a reduced line speed and smaller trains leading to higher operating costs. Many narrow gauge railways have been abandoned or converted to standard gauge. Industrial railways are often constructed using narrow gauge. Sugar cane and banana plantations are often served by narrow gauges such as, as there is little through-traffic to other systems.

The most widely used narrow gauges are
 * Cape gauge (e.g. Southern and Central Africa, Indonesia, Japan, Taiwan, Philippines, parts of Australia, New Zealand, Honduras and Costa Rica.)
 * metre gauge (e.g. SE Asia, 17000 km in India, but gauge conversion with Project Unigauge, East Africa, South America)
 * (e.g. in Sri Lanka Kelani Velley and Udapussellawa lines. All of this gauge tracks were converted into )

There are also minimum gauge railways.

Measurement and units
An 1845 Act of Parliament fixed British track gauges at 4 ft 8½ in and Irish track gauges at 5 ft 3 in. The 4 ft 8½ in gauge was the basis of 60 % of the world's railways, but is expressed as 1435 mm (including the United Kingdom ) - a decrease of 0.1 mm, but well within the engineering tolerances. The Irish 5 ft 3 in gauge is now referred to as a 1600 mm gauge – the difference between the metric and imperial values being 0.2 mm, again well within engineering tolerances.

Break of gauge
When a railway line of one gauge meets a line of another gauge there is a break of gauge. A break of gauge adds cost and inconvenience to traffic that passes from one system to another.

An example of this is on the Transmongolian Railway, where Russia and Mongolia use broad gauge while China uses standard gauge. At the border, each carriage has to be lifted in turn to have its bogies changed. The whole operation, combined with passport and customs control, can take several hours.

Other examples include crossings into or out of the former Soviet Union: Ukraine/Slovakia border on the Bratislava-L'viv train, and from the Romania/Moldova border on the Chişinău-Bucharest train.

This can be avoided however by implementing a system similar to that used in Australia, where some lines between states using different gauges were converted to dual gauge with three rails, one set of two forming a standard gauge line, with the third rail either inside or outside the standard set forming rails at either narrow or broad gauge. As a result, trains built to either gauge can use the line. However gauges must differ a minimum of twice the width of a rail to allow such a system.

Dual gauge
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, Spain, Tunisia and Vietnam.

When a third rail was proposed to allow dual gauge between Irish gauge and Standard gauge in Australia, the gauge difference of 6.5 inches was considered too small to allow the third rail to operate safely.

Variable gauge axles
Variable gauge axles (VGA), developed by the Talgo company and Construcciones y Auxiliar de Ferrocarriles (CAF) of Spain, amongst others, 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 (SUW 2000 and INTERGAUGE variable axles system). China and Poland are standard gauge, while Central Asia and Russia are gauge.

Designed for conversion
Equipment can be designed for easy conversion, such as the Garratt locomotives on the Kenya and Uganda Railway designed for conversion from to. Several classes of steam locomotives of the Victorian Railways were designed for easy conversion from to. Only one, R766, a preserved historic locomotive, has actually been converted.

Future
Further standardisation of rail gauges seems likely, as individual countries seek to build inter-operable national networks, and international organisations 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 standardise track gauge, signalling and electrical power systems. EU funds have been dedicated to assist Baltic states of Lithuania, Latvia, and Estonia in the construction of some key railway lines (Rail Baltica) in the standard gauge instead of their 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 developed plans for improved freight rail links between Spain, Portugal, and the rest of Europe. The problem within the EU is not so much rail gauge but loading gauge especially for the United Kingdom which has standard rail gauge but generally one of the smallest loading gauges in the world (relative to rail gauge).

High speed
Except in Russia and Finland, all high-speed rail systems use standard gauge, even in countries like Japan, Taiwan, Spain and Portugal where most of the existing rail lines use a different gauge.

Mining
Heavy duty mining railways which have little interconnection with other lines, such as in the Pilbara region of Western Australia, also tend to choose standard gauge to allow them to use off-the-shelf equipment, especially heavy-duty rolling stock.

New lines
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 have mechanized facilities at the breaks of gauge to move shipping containers from train to train rather than widespread gauge conversion.


 * Rail lines for iron ore to Oakajee port in Western Australia are proposed to form 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. This line owned by Sundance Resources may be shared with Legend Mining.

Kenya-Uganda-Sudan proposal
A proposal was aired in October 2004 to build a high-speed electrified line to connect Kenya with southern Sudan. Kenya and Uganda use gauge, while Sudan uses  gauge. Standard gauge was proposed for the project.

Latin America

 * 2008: Proposed link between Venezuela and Colombia
 * 2008: Venezuela via Brazil to Argentina - standard gauge
 * 2008: A proposed metre gauge line across Southern Paraguay to link the Argentine rail at Resistencia to the Brazilian line at Cascavel; both those lines are metre gauge, and the new line would allow uninterrupted "bioceanic" running from one coast to the other, from the Atlantic port of Paranaguá in Brazil to that of Antofagasta in Chile on the Pacific.

Temporary Way
The Permanent Way is so called because there is often a "Temporary Way" used for construction purposes and which is replaced by the "Permanent Way" when construction of the right of way nears completion.

The actual gauge of this temporary way is poorly documented, but it would generally be narrower than the permanent gauge.

In restricted spaces such as tunnels, the temporary way might be double track, even though the tunnel will ultimately be single track. Thus the Airport Rail Link in Sydney had construction trains of gauge which were replaced by the permanent tracks of  gauge.

The narrower the temporary way, the quicker it can be built. During World War II, it was proposed to expedite a Yunnan-Burma railway using a tiny "toy" 1 ft 3.3in gauge, since such a small gauge can have the tightest of curves in difficult terrain.

The professional body for track designers and installers is called the Permanent Way Institution.