With railways, a break of gauge occurs where a line of one track gauge (the distance between the rails, or between the wheels of trains designed to run on those rails) meets a line of a different gauge. Trains and rolling stock generally cannot run through without some form of conversion between gauges, leading to passengers having to change trains, and freight having to be transloaded or transshipped. That can cause delays, added costs, and inconvenience to those travelling on affected routes.
History Break of gauge was a common problem in the early days of railways, because standards had not yet been set and different organizations each used their own favored gauge on the lines they controlled. That was sometimes for mechanical and engineering reasons (optimizing for geography or particular types of load and rolling stock), and sometimes for commercial and competitive reasons (interoperability, or the lack of it, within and between companies and alliances were often key strategic considerations).
Even in the early era of railways in Britain, various solutions other than transloading were conceived,.. including rollbocks, transporter wagons, dual gauge track or variable gauge axles, and containerization of freight, but they were not implemented at the height of the Gauge War in the 1840s, which resulted the need for time-consuming and expensive transloading.
In his biography of Isambard Kingdom Brunel (key proponent of the broad gauge for the Great Western Railway), L. T. C. Rolt remarks on the apparent mysteriousness of that lack of implementation, but a likely explanation is that the combatants at the time were primarily interested in winning the Gauge War, and establishing a standard that benefited their commercial interests.
The lack of a standardized gauge was a significant problem in transportation in the Confederate States of America during the American Civil War.
See the examples section below for a range of international examples of different types, including a break of gauge in Gloucester, which was the earliest significant break of gauge between the and systems, and the first break of gauge between Russian and standard gauge built in 1861 between the border stations of Eydtkuhnen (then East Prussia, now Russia) and Kybartai (then Russia, now Lithuania).
Overcoming a break of gauge Transloading
Where trains encounter a different gauge, such as at the borders between Spain and France or between Russia and China, the traditional solution has been transloading (often called transshipment in discussions of break of gauge), that is, the transfer of passengers and freight to cars on the other system. When transloading from one gauge to another, often the quantities of rolling stock are unbalanced between the two systems, leading to more idle rolling stock on one system than the other.
Bogie exchange and variable gauge
One common method to avoid transshipment is to build cars to the smaller of the two systems' loading gauges with bogies that are easily removed and replaced with other bogies at an interchange location on the border. This takes a few minutes per car, but is quicker than transshipment of goods.
A more modern and sophisticated method is to have multigauge bogies with wheelsets whose wheels can be moved inwards and outwards. Normally they are locked in place, but special equipment at the border unloads and unlocks the wheels and pushes them inward or outward to the new gauge, relocking and reloading the wheels when done. This is done as the train moves slowly over the special equipment. Stadler Rail make one brand of Variable Gauge Axle (VGA) system.
Dual gauge and track gauge conversion
In some cases, breaks of gauge are avoided by installing dual-gauge track, either permanently or as part of a changeover process to a single gauge.
Piggyback operation
One method of achieving interoperability between rolling stock of different gauges is to piggyback stock of one gauge on special transporter wagons or even ordinary flat wagons fitted with rails. 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 work in the 1950s to bypass steep gradients and washaways in the Flinders Ranges.
Narrow-gauge railways were favoured in the underground slate quarries of North Wales, as tunnels could be smaller. The Padarn Railway operated transporter wagons on their gauge railway, each carrying four slate trams. When the Great Western Railway acquired one of the narrow-gauge lines in Blaenau Ffestiniog, it deployed a similar type of transporter wagon to allow continued use of the quarries' existing slate wagons.
Transporter wagons are most commonly used to transport narrow-gauge stock along standard-gauge lines. Sometimes whole trains of one gauge are loaded onto rails mounted on wagons of the other gauge. This occurred between Port Pirie and Maree for a short while in the 1950s.
At the Guinness brewery in Dublin there used to be internal narrow gauge and gauge (standard gauge for Ireland), and to avoid the need for steam locomotives of both gauges the narrow-gauge engines were provided with standard-gauge converter wagons (named "haulage trucks"). The narrow-gauge steam locomotive was lowered into the haulage truck using a gantry, and its wheels rested on rollers, which in turn drove the haulage wagon wheels via a 3:1 reduction gear. Several of these locomotives survived into preservation, including locomotive No23 complete with haulage wagon and lifting gantry preserved at Brockham museum in 1966, and now at the Amberley Museum Railway.
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.
, Japan is developing the Train on Train piggyback concept, though this project has been abandoned by 2020.
Containerisation
The internationally widespread use of standard intermodal containers since the 1960s has made break of gauge less of a problem, since containers can be efficiently transferred from one mode or train to another by specialized cranes.
Greater efficiency is achieved when the lengths of the wagons on each gauge are the same, so that the containers can be transferred from one train to the other with no longitudinal movement. The speed of the transfer depends, among other factors, on how many cranes can operate simultaneously at the transfer location.
Container cranes are relatively portable, so that if the break of gauge transshipment hub changes from time to time, the cranes can be moved around as required. Fork lift trucks can also be used.
For example, when containers are shipped by a "direct train" from China to Europe, it is only containers, and not the railcars, which move from China's railway network to that of Kazakhstan. At the Altynkol railway station near the border at Khorgos, two trains (the Chinese one and the Kazakh one) are placed side by side at parallel tracks, while gantry cranes move the containers from one train to the other in as short a time as 47 minutes.See satellite views of Altynkol railway station using coordinates in that article.
Types Minor breaks of gauge Wherever there are narrow-gauge lines that connect with a standard-gauge line, there is technically a break of gauge. If the amount of traffic transferred between lines is small, this might be a small inconvenience only. In Austria and Switzerland there are numerous breaks-of-gauge between standard-gauge main lines and narrow-gauge railways.
Many internal Swiss railways that operate in the more mountainous regions are , and most are equipped with rack assistance to deal with the relatively steep gradients encountered. Through running of standard-gauge trains on rack sections would not be possible, but dual-gauge track exists in many places where the gradient is relatively flat to carry standard- and metre-gauge stock. There are also some 800-mm-gauge railways which are entirely rack operated.
The effects of a minor break of gauge can be minimized by placing it at the point where a cargo must be removed from cars anyway. An example of this is the East Broad Top Railroad in the US, which had a coal wash and preparation plant at its break of gauge in Mount Union, Pennsylvania. The coal was unloaded from narrow-gauge cars of the EBTR, and after processing was loaded into standard-gauge cars of the Pennsylvania Railroad.
Nominal breaks of gauge The line between Finland and Russia has a nominal break of gauge; Finnish gauge is whereas Russian gauge is ; the present Russian gauge is actually a redefinition of the older . This does not usually prevent through-running – service running across both gauges exists in the form of the Allegro high-speed service between Helsinki and St. Petersburg. The nominal difference is generally within operating tolerances and does not cause problems or delays.
The Iberian gauge is actually three slightly different gauges: in Spain, in Portugal, and the newer, redefined . Through-running is done with vehicles having a gauge within certain tolerances. Indian gauge, , is also compatible with Iberian gauge, although there are no actual railway connections between the two. Despite this, old Spanish and Portuguese rolling stock have been reused in Argentina and Chile, both of which use Indian gauge.
A nominal break of gauge with standard gauge exists as well: on the Hong Kong MTR network, lines owned by MTR Corporation used before 2014. Newer lines and extensions use with nominal gauge break at Sheung Wan station and Yau Ma Tei station. is also employed on those owned by KCR Corporation, despite the lack of physical connections between the two networks.
Other types of breaks A large railway may have main lines with heavy tracks, and branch lines with light track. Light locomotives and rolling stock can operate on all lines, but heavy locomotives and rolling stock can only operate on heavy track. Heavy rolling stock might be able to operate on lighter track at reduced speed. Light track can be upgraded to heavy track by installing heavy rails, etc., and this can be done without changing the track gauge.
Gauge conversions
Gauge orphan When a main line is converted to a different gauge, branch lines can be cut off and made relatively useless, at least for freight trains, until they too are converted to the new gauge. These severed branches can be called gauge orphans.
Gauge outreach The opposite of a gauge orphan is a line of one gauge which reaches into the territory composed mainly of another gauge. Examples include five broad-gauge lines from Victoria, Australia, which crossed the border into otherwise standard-gauge New South Wales. Similarly, the standard-gauge line from Albury to Melbourne in 1962 which eliminated most transshipment at Albury, especially the need for passengers to change trains in the middle of the night. The standard-gauge outreach from Kalgoorlie to Perth partly replaced the original narrow-gauge line, and partly rebuilt that line with better curves and gradients as double-track dual gauge. Because of lack of space at the main Perth station, standard-gauge passenger trains terminate three stations short at East Perth.