Railway's track gauges

Table of contents

• Table of contents
• History
• Advantages and disadvantages of different track gauges
  • Orographic factor
  • Economic factor
  • Military strategy
• Comparison of various railway track gauges
• Distribution of track gauge by country
• Reference

Track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge.

Track gauge distance generic representation

Even within a given railway line, the distance between rails is not constant. The conicity of the wheel/rail contact induces a self-centring of the wheelset, especially in curves. In order to minimice the wheel flange contact with the active edge of the rails when the wheelset moves sideways, a gauge widening is applied to all curves. This varies depending on the curve radius as well as on the nominal distance between the rails and the specific practice of each country.

Since the Technical Unity of Railways (TU) adopted an agreement on gauging at their 1914 meeting in Berne: tracks known as “standard” have a nominal gauge of 1435 mm between the rails, and a minimum value of 1432 mm. Gauge widening in curves is allowed up to 1465 mm, with a rail wear related maximum dimension of 1470 mm, which should never be exceeded.

There are 2 other gauges to ensure compliance with a required standard:

• Loading gauge. Two-dimensional profile that encompasses a cross-section of the track, a rail vehicle and a maximum-sized load.
• Structure gauge. Specifies the outline into which structures (bridges, platforms, lineside equipment etc.) must not encroach.

History

You’ve probably already noticed that given track gauges are in feet. And you’ve probably assumed that they are English feet, also known as “imperial” feet. That’s not just the case, almost all current gauges were set in Britain before 1846.

In the 19th century, mining wagons in England had a spacing of between 1.40 and 1.50 m, adapted for horses. Then, Richard Trevithick introduced steam power into these mines inventing the railway. Later, George Stephenson developed a highly successful design of locomotive for the Killingworth mines railway. This led to the Stockton and Darlington Railway using its locomotives with a gauge of 4 ft 8 in (1,422 mm) in 1825. Due to the success of this line, the first inter-city line, the Liverpool and Manchester Railway, also used this gauge. This gauge was later adjusted to 4 ft 8.5 in (1,435 mm) to improve handling on curves. Finally, this dimension became the international standard.

Advantages and disadvantages of different track gauges

Orographic factor

On the one hand, wide track gauges, especially in the first decades of steam locomotive development, allowed the use of machines with wider boilers (increasing their power), and/or the use of larger wheels to be able to travel faster (placing the boilers in the middle, and not above the wheels).

On plains, these track widths were very convenient as they allowed more cargo to be transported more quickly. And in areas with steep slopes, these widths were needed to be able to use more powerful locomotives that could climb those slopes.

In Europe, for example, most high-speed lines use standard track gauge, while in Asia, where distances are longer, even wider track gauges are used to allow higher speeds.

However, the rapid improvement of steam engines in the following decades caused these arguments to lose the weight they initially had.

On the other hand, narrow gauges are very convenient in mountainous areas with sharp curves, giving greater maneuverability to the trains, which also had to be lighter. Another point in favor of narrow gauges is that they allow for lower costs in the construction of tunnels.

In Spain, historically, for long distances a wider gauge was chosen to obtain greater profitability, and for shorter and very steep sections, where the layout was winding and complicated, the narrow gauge was chosen, because it was more economical.

Economic factor

In some cases, countries have opted for narrower track gauges as a way to reduce track construction and maintenance costs.

In other cases, countries adopted** different gauges as a protectionist measure. **In practice, however, changing track gauges is an obstacle to both imports and exports. And despite the high costs associated with standardizing the infrastructure, the long-term trend is to unify gauges between neighboring systems due to its clear advantages, as has already occurred in England, Europe, the United States and Canada.

Military strategy

Another theory is that when the first European railway network was established between 1820 - 1850, the memory of the Napoleonic Wars was still fresh in the minds of the people. Having a different gauge than the enemy nations would mean that, in the event of an invasion, the enemy would not be able to use its own trains to transport its troops, as these would not be able to run on a different gauge.

Respecto a la creación de la red ferroviaria Española. En el número 190 de la “Revista Bibliográfica de Geografía y Ciencias Sociales”, que edita la Universidad de Barcelona, encuentro lo siguiente:

“Cabe la posibilidad de que, en la determinación del ancho de vía español, existiese implícita una estrategia destinada a obstaculizar una hipotética invasión militar ante el reciente e ingrato recuerdo de la Guerra de la Independencia. Sin embargo no parece que la Comisión redactora del informe adoptara esta medida por razones de estrategia, pues no menciona en ningún momento la cuestión militar y parece que lo que prima en el informe es el factor determinante del relieve de nuestro país ante el cual se necesitan locomotoras de mayor potencia: Para este efecto conviene aumentar el ancho de las vías”.

In practice, however, the German army narrowed 28,700 km of track (from the Russian gauge of 1520 mm to the standard gauge of 1435 mm) during its advance through the USSR between 1941 and 1943. If the aim is to prevent an invasion, the best option is to install much narrower gauge tracks, which would make it impossible for larger trains to pass through tunnels and on bridges.

Comparison of various railway track gauges

Distribution of track gauge by country

Figure shows the gauge which is currently most used in each country (main color), with other significant gauges used depicted as small squares on top of the main color. Grey indicates no railways. Overview of the track gauge worldwide

Reference

• openrailwaymap
• https://en.wikipedia.org/wiki/Track_gauge
• https://www.grijalvo.com/Aristogeronte/Ancho_via.htm
• https://www.ub.edu/geocrit/b3w-190.htm
• Plaquin, B. (n.d.). 4.1 Railway gauges. In Rolling Stock in the Railway System (2020th ed., Vol. 1, pp. 260–273). essay, Trackomedia.