Loading gauge

 ( Permanent Way ) 

A loading gauge is a diagram or physical structure that defines the maximum height and width of rail transport rolling stock and their loads. The loading gauge is to ensure that rail vehicles can pass safely through tunnels and under bridges, and keep clear of platforms, trackside buildings and other structures. Classification systems vary between different countries, and loading gauges may vary across a network, even if the track gauge is uniform.

The term loading gauge can also be applied to the maximum size of road in relation to , and , and garage door into automobile repair shops, , , residential garages, multi-storey car parks and .

A related but separate gauge is the structure gauge, which sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. The difference between these two gauges is called the clearance. The specified amount of clearance makes allowance for the oscillation of rail vehicles at speed.

Over time, there has been a trend towards less restrictive loading gauges and greater standardization of them. Some older systems and lines have had their expanded by raising bridges, increasing the height and width of tunnels and making other necessary alterations. Containerisation, and a trend towards larger shipping containers, has led rail operators to increase loading and structure gauges to compete with road haulage.

The term "loading gauge" can also refer to a physical structure, sometimes using electronic detectors using electric eye on an arm or gantry placed over the exit lines of goods yards or at the entry point to a restricted part of a network. The devices ensure that loads stacked on open or flat wagons stay within the height/shape limits of the line's bridges and tunnels, and prevent out-of-gauge rolling stock entering a stretch of line with a smaller loading gauge. Compliance with a loading gauge can be checked using a clearance car. In the past, they were simple wooden frames or physical feelers mounted on rolling stock. More recently, laser beams have been used.

The loading gauge is the maximum size of rolling stock. It is distinct from the structure gauge, which sets limits to the size of bridges and tunnels on a rail line, allowing for engineering tolerances and the motion of rail vehicles. The difference between the two is called the clearance. The terms "dynamic envelope" or "kinematic envelope", which include factors such as suspension travel, overhang on curves (at both ends and middle) and lateral motion on the track, are sometimes used in place of loading gauge.

Railway platform height is also a consideration for the loading gauge of passenger trains. Where the two are not directly compatible, stairs may be required, which will increase loading times. Where long carriages are used at a curved platform, there will be platform gap, causing risk. Problems increase where trains of several different loading gauges and vehicle floor heights use (or even must pass through) the same platform.

The size of load that can be carried on a railway of a particular gauge is also influenced by the design of the rolling stock. Low-deck rolling stock can sometimes be used to carry taller shipping containers on lower gauge lines although their low-deck rolling stock cannot then carry as many containers.

Rapid transit (metro) railways generally have a smaller loading gauge, which reduces the cost of tunnel construction. Those systems have to use their own specialised rolling stock.

• Operate at low speed, especially in places with limited clearance, such as platforms.
• Cross over from a track with inadequate clearance to another track with greater clearance, even if there is no signalling to allow this.
• Prevent operation of other trains on adjacent tracks.
• Use refuge loops to allow trains to operate on other tracks.
• Use of (special rolling stock) that manipulate the load up and down or left and right to clear obstacles.
• Remove (and later replace) obstacles.
• Use gauntlet track to shift the train to side or center.
• For locomotives that are too heavy, ensure that fuel tanks are nearly empty.
• Turn off power in overhead wiring or in the third rail (use diesel locomotive)
• Permanently adapt a certain route to larger gauge if there is repeated need for such trains.

This often results in increased costs for purchasing new trainsets or locomotives as they must be specifically designed for the existing British network, rather than being purchased "off-the-shelf". For example, the new trains for HS2 have a 50% premium applied to the "classic compatible" sets that will be "compatible" with the current (or "classic") rail network loading gauge as well as the HS2 line. The "classic compatible" trainsets will cost £40million per trainset whereas the HS2-only stock (built to European loading gauge and only suitable to operate on HS2 lines) will cost £27M per trainset despite the HS2-only stock being physically larger.

It was recognized even during the nineteenth century that this would pose problems and countries whose railroads had been built or upgraded to a more generous loading gauge pressed for neighboring countries to upgrade their own standards. This was particularly true in continental Europe where the Nordic countries and Germany with their relatively generous loading gauge wanted their cars and locomotives to be able to run throughout the standard gauge network without being limited to a small size. France, which at the time had the most restrictive loading gauge ultimately compromised giving rise to Berne gauge which came into effect just before World War I.

Military railways were often built to particularly high standards, especially after the American Civil War and the Franco-Prussian War showed the importance of railroads in military deployment as well as mobilization. The German Empire was particularly active in the construction of military railways which were often built with great expense to be as flat, straight and permissive in loading gauge as possible while bypassing major urban areas, making those lines of little use to civilian traffic, particularly civilian passenger traffic. However, all those aforementioned factors have in some cases led to the subsequent abandoning of those railroads.

The loading gauge affected tank design, with the 1945 British Centurion tank the first British tank allowed to exceed the restricted British loading gauge. The 1944 German Tiger II tank had to be changed to narrower transport tracks instead of battle tracks for transport by rail.

• PPI – the predecessor of the UIC gauges had the maximum dimensions with an almost round roof top.
• UIC A: The smallest (slightly larger than PPI gauge). Images do not load Maximum dimensions .
• UIC B: Slightly larger than the UIC on the roof level. Maximum dimensions .
• UIC B+: New structures in France are being built to UIC B+. Up to has a shape to accommodate tractor-trailers loaded with ISO containers.
• UIC C: The Central European gauge. In Germany and other central European countries, the railway systems are built to UIC C gauges, sometimes with an increment in the width, allowing Scandinavian trains to reach German stations directly, originally built for Soviet freight cars. Maximum dimensions .

The designation of a GB+ loading gauge refers to the plan to create a pan-European freight network for ISO containers and trailers with loaded ISO containers. These container trains ( piggy-back trains) fit into the B envelope with a flat top so that only minor changes are required for the widespread structures built to loading gauge B on continental Europe. A few structures on the British Isles were extended to fit with GB+ as well, where the first lines to be rebuilt start at the Channel Tunnel.

Owing to their historical legacies, many member states' railways do not conform to the TSI specification. For example, Britain's role at the forefront of railway development in the 19th century has condemned it to the small Structure gauge of that era. Conversely, the s of countries that were satellites of the former Soviet Union are much larger than the TSI specification. Other than for GB+, they are not likely to be retrofitted, given the enormous cost and disruption that would be entailed.

Network Rail uses a W loading gauge classification system of freight transport ranging from W6A (smallest) through W7, W8, W9, W9Plus, W10, W11 to W12 (largest). The definitions assume a common "lower sector structure gauge" with a common freight platform at above rail.

In addition, gauge C1 provides a specification for standard coach stock, gauge C3 for longer Mark 3 coaching stock, gauge C4 for Pendolino stock and gauge UK1 for high-speed rail. There is also a gauge for locomotives. The size of container that can be conveyed depends both upon the size of the load that can be conveyed and the design of the rolling stock.

• W6A: Available over the majority of the British rail network.
• W8: Allows standard high shipping containers to be carried on standard wagons.
• W9: Allows high Hi-Cube shipping containers to be carried on "Megafret" wagons that have lower deck height with reduced capacity. At wide, it allows for wide Euro shipping containers, which are designed to carry Euro- efficiently
• W10: Allows high Hi-Cube shipping containers to be carried on standard wagons and also allows wide Euro shipping containers. Larger than UIC A.
• W11: Little used but larger than UIC B.
• W12: Slightly wider than W10 at to accommodate refrigerated containers. Recommended clearance for new structures, such as bridges and tunnels.
• UIC GC: Channel Tunnel and Channel Tunnel Rail Link to London; with proposals to upgrade the Midland Main Line northwards from London to GB+ standards.

A strategy was adopted in 2004 to guide enhancements of loading gauges and in 2007 the freight route utilisation strategy was published. That identified a number of key routes where the loading gauge should be cleared to W10 standard and, where structures are being renewed, that W12 is the preferred standard.

Height and width of containers that can be carried on GB gauges (height by width). Units as per source material.

• W9: by
• W10: by
• W11: by
• W12: by

• The City and South London Railway was built with tunnels of only diameter. Enlarged for Northern line to
• The Central line has tunnels of , increasing on curves and narrowing to near stations. This makes Central line trains unique on the London Underground because although the rolling stock's loading gauge is the same as the other Tube lines, the smaller tunnels require the positive Fourth rail rail to be higher than on all other lines.

A Parliamentary committee headed by James Stansfeld then reported on 23 May 1892, "The evidence submitted to the Committee on the question of the diameter of the underground tubes containing the railways has been distinctly in favour of a minimum diameter of ". After that, all tube lines were at least that size.

• Piccadilly line with tunnels of
• Victoria line with tunnels of ; enlarged to reduce air friction.
• Glasgow Subway with tunnels of and a unique track gauge of only .
• Tyne and Wear Metro with tunnels of ; built to mainline rail network standards.

Both SE-A and SE-C are defined for straight track, with the corresponding structure gauge. On curved track, the structure gauge is widened to allow the 24-metre reference vehicle to pass. By European standards, SE-C is unusually large, permitting vehicles up to 24 metres long and almost 4 metres wide. However, vehicles with softer suspension that allows greater lateral movement must be narrower to remain within the kinematic reference profile.

• Betuweroute: to allow double stacked container trains in the future. The present overhead line does not allow this height, as it has to follow standards.

• Channel Tunnel:

gauge for the United Kingdom and Sierra Leone: