Track gauge

[1] 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.

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".

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, 4 ft 8 in (1,422 mm).

When Bristol promoters planned a line from London, they employed the innovative engineer Isambard Kingdom Brunel.

Some smaller concerns selected other non-standard gauges: the Eastern Counties Railway adopted 5 ft (1,524 mm).

The larger railway companies wished to expand geographically, and large areas were considered to be under their control.

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.

As railways were built in other countries, the gauge selection was pragmatic: the track would have to fit the rolling stock.

In modern usage, the term "broad gauge" generally refers to track spaced significantly wider than 1,435 mm (4 ft 8+1⁄2 in).

Very narrow gauges of under 2 feet (610 mm) were used for some industrial railways in space-restricted environments such as mines or farms.

Through operation between railway networks with different gauges was originally impossible; goods had to be transshipped and passengers had to change trains.

[17] A system developed by Talgo and Construcciones y Auxiliar de Ferrocarriles (CAF) of Spain uses variable gauge wheelsets; at the border between France and Spain, through passenger trains are drawn slowly through an apparatus that alters the gauge of the wheels, which slide laterally on the axles.

During this period, many locations practicality required mixed gauge operation, and in station areas the track configuration was extremely complex.

For example, MacDermot[20] wrote: In November 1871 a novelty in the shape of a mixed-gauge goods train was introduced between Truro and Penzance.

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.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.

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

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.

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.

[24] Speed, capacity, and economy are generally objectives of rail transport, but there is often an inverse relationship between these priorities.

For routes with high traffic, greater capacity may more than offset the higher initial cost of construction.

A major barrier to achieving interchangeability, however, is path dependence[29] – in this context the persistence of an already adopted standard to which equipment, infrastructure and training has become aligned.

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 gauges that are too small to allow the larger rolling stock of continental Europe to operate in the UK.

When interchangeability has not been achieved, freight and passengers must be transferred through time-consuming procedures requiring manual labour and substantial capital expenditure.

[30] Some bulk commodities, such as coal, ore, and gravel, can be mechanically transshipped, but even this is time-consuming, and the equipment required for the transfer is often complex to maintain.

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.

The EU has developed plans for improved freight rail links between Spain, Portugal, and the rest of Europe.

[37] The plan is managed by infrastructure ministers from participating East African Community countries in association with transport consultation firm CPCS Transcom.