Standard gauge



The standard gauge (also named the Stephenson gauge after George Stephenson) is a widely-used rail gauge. Approximately 60% of the world's existing railway lines are built to this gauge (see the list of countries that use the standard gauge). The distance between the inside edges of the rails of standard gauge track is.

History
As railways developed and expanded one of the key issues to be decided was that of the rail gauge (the distance, or width, between the inner sides of the rails) that should be used. The eventual result was the adoption throughout a large part of the world of a "standard gauge" of, allowing inter-connectivity and the inter-operability of trains. In England some early lines in colliery areas in the north east of the country were built to a gauge of ; and in Scotland some early lines were (Scotch gauge). By 1846, in both countries, these lines were widened to standard gauge. Parts of the United States rail system, mainly in the northeast, adopted the same gauge because some early trains were purchased from Britain. However, until well into the second half of the 19th century Britain and the USA had several different track gauges. The American gauges slowly converged as the advantages of equipment interchange became more and more apparent; the destruction of much of the South's broad gauge system in the American Civil War hastened this trend.

Origins
A popular legend traces the origin of the gauge even further back than the coalfields of northern England, pointing to the evidence of rutted roads marked by chariot wheels dating from the Roman Empire. This legend has been debunked. The historical tendency to place the wheels of horse-drawn vehicles approximately apart probably derives from the width needed to fit a carthorse in between the shafts. In addition, while road-traveling vehicles are typically measured from the outermost portions of the wheel rims (and there is some evidence that the first railroads were measured in this way as well), it became apparent that for vehicles traveling on rails, it was better to have the wheel flanges located inside the rails, and thus the distance measured on the inside of the wheels (and, by extension, the inside faces of the rail heads) was the important one.

There was no standard gauge for horse railways, but there were rough groupings: in the north of England none were less than 4ft. Wylam collery's system, built before 1763, was 5ft 0in; as was John Blenkinsop's Middleton Railway, the old 4ft plateway was relaid to 5ft so that Blenkinsop's engine could be used. Others were 4ft 4in Beamish or 4ft 7.5in (Bigges Main and Kenton and Coxlodge).

The English railway pioneer George Stephenson spent much of his early engineering career working for the coal mines of County Durham. He favoured 4ft 8in for waggonways in Northumberland and Durham and used it on his Killingworth line. The Hetton and Springwell waggonways also used the gauge.

Stephenson's Stockton and Darlington railway (S&DR) was built primarily to transport coal from several mines near Shildon to the port at Stockton-on-Tees. The S&DR's initial track gauge of was set to accommodate the existing gauge of hundreds of horse-drawn chaldron wagons that were already in use on the wagonways in the mines. It was built and used at this gauge for fifteen years before being changed to gauge.

The beginnings of the 4ft 8&frac12;in gauge
George Stephenson used the gauge (with an extra half-inch of free movement to reduce binding on curves ) for the Liverpool and Manchester Railway, authorised in 1826 and opened 30 September 1830. The success of this project led to George Stephenson and his son Robert being employed to engineer several other larger railway projects. However, the Chester and Birkenhead Railway, authorised on 12 July 1837, was 4ft 9in; the Eastern Counties Railway, authorised on 4 July 1836, was 5ft 0in; London and Blackwall Railway, authorised on 28 July 1836, was 5ft 0in; the London and Brighton Railway, authorised on 15 July 1837, was 4ft 9in; the Manchester and Birmingham Railway, authorised on 30 June 1837, was 4ft 9in; the Manchester and Leeds Railway, authorised on 4 July 1836, was 4ft 9in the Northern and Eastern Railway, authorised on 4 July 1836, was 5ft 0in. The 4ft 9in railways were intended to take gauge vehicles and allow a running tolerance.

The influence of the Stephensons appears to be the main reason that the gauge became the standard, and its usage became more widespread than any other gauge. .

The Royal Commission
In the United Kingdom of Great Britain and Ireland, a Royal Commission in 1845 reported in favour of a standard gauge. In Great Britain, Stephenson's gauge was chosen as the standard gauge on the grounds that lines built to this gauge were eight times longer than that of the rival gauge, adopted principally by the Great Western Railway. The subsequent Gauge Act of 1846 ruled that new passenger-carrying railways in Great Britain should be built to a standard gauge of ; and those in Ireland to a standard gauge. It allowed the broad gauge companies in Great Britain to continue repairing their tracks and expanding their networks within the Limits of Deviation and the exceptions defined in the Act. After an intervening period of mixed-gauge operation (tracks were laid with three running-rails), the Great Western Railway finally converted its entire network to standard gauge in 1892.

Ideal gauge
Subsequently, engineers have shown that a narrow gauge is less than ideal: despite usually offering cheaper construction, a smaller gauge restricts speeds due to a reduced load stability. Broader gauges are theoretically more stable at speed and allow larger, wider, heavier loads. According to Isambard Kingdom Brunel's studies the optimum gauge for a rail system (and the one he originally used on his Great Western Railway) is 7 ft (2100 mm).

There has been much controversy about what constitutes the "ideal gauge". From a design point of view, a train can travel faster around a given radius of track if the gauge is wider, as the centre of gravity of the train is further displaced from the wheels, which in turn lowers the angle between the wheel's lower contact surface to the centre of gravity, and horizontal. Given that one can tailor either the track radius for train speed, or the train speed for track radius, gauge in some cases may not be as important as interoperability.

There are many examples of high speed and high mass applications on narrow gauges throughout the world, suggesting that gauge is less important than the original supporters of either broad gauge or narrower gauges held it to be:


 * The heaviest trains in the world run on standard gauge track in Australia, North America and Mauritania. Gauge is not the limiting factor in running heavier trains.
 * The fastest conventional trains in the world also run on standard gauge in Japan and Europe, where speeds over 300 km/h are attained.
 * Very heavy trains run on the narrow gauge of in Queensland (Australia) and South Africa, on track as strong as heavy standard gauge track. This narrow gauge does not seem to materially affect the weight of trains that can be run on it.
 * Fairly fast trains (160 km/h) can run on track, as can be seen in Japan and Queensland.
 * It is possible to build a light standard gauge line about as cheaply as a narrow gauge line.
 * It is possible to build a narrow gauge line to as heavy-duty a standard as a standard gauge line.
 * Loading gauge, structure gauge, axle load, compatibility of couplings, continuous brakes, electrification systems, railway signal systems, radio systems and rules and regulations are also important.

With the benefit of hindsight, little was gained by building railway systems too narrow (down to about ) or too broad (up to about 7 ft (2100 mm)) gauges, and this was at the cost of limited interoperability. For an example of the difficulties of interoperability see the ramsey car transfer apparatus and the variable gauge axles used to transfer cars between different gauges of track.

Only in gauges of less than can a railway be built significantly more cheaply than is possible with standard gauge, and only then in mountainous terrain, or where a low capacity line is required, or with industrial railways where through running is not required.

It can be argued therefore, that the original uniform gauge adopted by Stephenson in 1830 can serve most of the tasks performed by gauges from 3 to 7 ft (900 to 2100 mm), albeit with a narrow gauge of about for cane tramways, underground mine, mountain, construction, temporary and military railways, plus children's railways.

As the advantages of interchange of equipment between lines became clear, so did standardization of gauge become attractive. Where these advantages are not compelling, use of non-standard gauges continue today.

Piggyback operation
One method of achieving interoperability between rolling stock of different gauges, is to piggyback stock of one gauge on special transporter wagons. This enables rolling stock to reach workshops and other lines of the same gauge to which they are not otherwise connected. Piggyback operation by the trainload occurred as a temporary measure between Port Augusta and Marree during gauge conversion works in the 1950s, to bypass steep gradients in the Flinders Ranges. Piggyback operation was a permanent feature of the Padarn Railway in North Wales.

Transporter wagons are most commonly used to transport narrow gauge stock over standard gauge lines. More rarely, standard gauge vehicles are carried over narrow gauge tracks using adaptor vehicles; examples include the Rollbocke transporter wagon arrangements in Germany, Austria and the Czech Republic and the milk transporter wagons of the Leek and Manifold Valley Light Railway in England.

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

An example of this is on the Transmanchurian Railway, where Russia and Mongolia use broad gauge while China uses the 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 any crossing 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 Chisinau-Bucharest train.

This can be avoided however by implementing a system similar to that used in Australia, where lines between states using different gauges are built as dual gauge. Thus the lines have 3 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.

Standard gauge in model railways
In American model railroading, standard gauge was originally an effort by Lionel Corporation to corner the U.S. market in the early years of the 20th century. Lionel standardized its offerings on three-rail track with a gauge of 2 1/8 in (54 mm) between the outer rails, making it incompatible with Gauge 1 offerings from European manufacturers. Lionel then registered a trademark on Standard Gauge. Other American companies followed Lionel's lead, standardizing on Lionel's new standard but calling it Wide gauge in order to avoid infringing on Lionel's trademark.

Standard gauge fell out of favour in the 1930s because of its high cost, and Lionel discontinued its Standard gauge offerings in 1940.

Although scale modeling was not of primary concern, standard gauge's scale is generally accepted at 1:26.59, making it somewhat smaller than G scale.

More recently, standard gauge has come to mean scale modelling in which the track is accurately scaled to real-world standard gauge. This is opposed to narrow gauge modeling, which models real-world narrow gauge, or off-scale modeling, where track is not true to scale, such as in O gauge and OO gauge.