- Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures. Classifications systems vary between different countries and gauges may vary across a network, even if the track gauge remains constant.
- 1 Introduction
- 2 History
- 3 Standard loading gauges for standard gauge lines
- 4 Broad gauge
- 5 Narrow gauge
- 6 Structure gauge
- 7 Sources
- 8 References
- 9 External links
The loading gauge determines the sizes of passenger trains and the size of shipping containers that can be conveyed on a section of railway line and varies across the world and often within a single railway system. Over time there has been a trend towards larger loading gauges and more standardization of gauges with older lines having their structure gauges enhanced by raising bridges, increasing the height of tunnels and making other necessary alterations. Containerisation and a trend towards larger shipping containers has led rail companies to increase structure gauges to compete effectively with road haulage.
The term loading gauge can also refer to the physical structure, sometimes using electronic detectors using light beams 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 stayed within the height/shape limits of the line's bridges and tunnels and prevent out-of-gauge rolling stock entering a region with a smaller loading gauge. Compliance with a loading gauge can be checked with a clearance car which in the past were simple wooden frames or physical feelers mounted on rolling stock and more recently lasers are used.
The loading gauge is maximum size of rolling stock which is distinct from the structure gauge which is minimum size of bridges and tunnels which must be larger to allow for engineering tolerances and car motion. 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.
The height of platforms is also a consideration when considering the loading gauge of passenger trains. Where the two are not directly compatible then steps may be required which will increase loading times. Where long carriages are used on a curving platform gaps will occur between the platform and the carriage door causing additional risk. Problems increase where trains of several different loading gauges and train floor heights use 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 9 ft 6 in (2.9 m) shipping containers on lower gauge lines although their low-deck rolling-stock cannot then carry as many containers.
Larger out-of-gauge loads can also sometimes be conveyed by taking one or more of the following measures:
- operate at low speed, especially at places with limited clearance such as platforms
- crossover from 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 special rolling stock that manipulate the load up and down or left and right to clear obstacles.
- remove (and later replace) obstacles.
- for locomotives that are too heavy, ensure that fuel tanks are nearly empty.
Rapid Transit (metro) railways generally have a very small loading gauge. This reduces the cost of tunnel construction. These systems only use their own rolling stock.
The loading gauge on the main lines of Great Britain, most of which were built before 1900, is generally smaller than in other countries. In mainland Europe, the slightly larger Berne gauge (Gabarit passe-partout international, PPI) was agreed in 1912 and came into force in 1914. As a result, British (passenger) trains have smaller loading gauges and smaller interiors, despite being standard gauge along with much of the world.
Standard loading gauges for standard gauge lines
International Union of Railways (UIC) Gauge
The International Union of Railways (UIC) has developed a standard series of loading gauges named A, B, B+ and C.
- PPI - the predecessor of the UIC gauges had the maximum dimensions 3.15 by 4.28 m (10 ft 4 in × 14 ft 0.5 in) with an almost round roof top.
- UIC A: The smallest (slightly larger than PPI gauge). Maximum dimensions 3.15 by 4.32 m (10 ft 4 in × 14 ft 2 in).
- UIC B: Most of the high-speed TGV tracks in France are built to UIC B. Maximum dimensions 3.15 by 4.32 m (10 ft 4 in × 14 ft 2 in).
- UIC B+: New structures in France are being built to UIC B+. Up to 4.28 m (14 ft 1 in) it features a width of 2.50 m (8 ft 2 in) to accommodate 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 to allow for Scandinavian trains to reach German stations directly. Maximum dimensions 3.15 by 4.65 m (10 ft 4 in × 15 ft 3 in).
In Continental Europe, the UIC directives were supplanted by ERA Technical Specifications for Interoperability Technical Specifications for Interoperability (TSI) of European Union in 2002 which has defined a number of recommendations to harmonize the train systems. The TSI Rolling Stock (2002/735/EC) has taken over the UIC Gauges definitions defining Kinematic Gauges with a reference profile such that Gauges GA and GB have a height of 4.35 m (14 ft 3 in) (they differ in shape) with Gauge GC rising to 4.70 m (15 ft 5 in) allowing for a width of 3.08 m (10 ft 1 in) of the flat roof. All cars must fall within an envelope of 3.15 m (10 ft 4 in) wide on a 250 m (12 ch) radius curve. The TGVs, which are 2.9 m (9 ft 6 in) wide, fall within this limit.
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. Currently some structures on the British Isles are extended to fit with GB+ as well, whereas the first lines to be rebuilt start at the channel tunnel.
A specific example of the value of these loading gauges is that they permit double decker passenger carriages. Although mainly used for suburban commuter lines (in France, Germany, Italy, the Netherlands and Spain, as well as other locations around the world), France is notable for using them on its high speed TGV services: the SNCF TGV Duplex carriages are 4.32 metres (14.2 ft) high.
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 1100 mm above rail.
In addition, C1 provides a specification for coach stock and 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 2.6 m (8 ft 6 in) high shipping containers to be carried on standard wagons.
- W9: Allows 2.9 m (9 ft 6 in) high Hi-Cube shipping containers to be carried on "Megafret" wagons which have lower deck height with reduced capacity. At 2.6 m (8 ft 6 in) wide it allows for 2.5 m (8 ft 2 in) wide Euro shipping containers which are designed to carry Euro-pallets efficiently
- W10: Allows 2.9 m (9 ft 6 in) high Hi-Cube shipping containers to be carried on standard wagons and also allows 2.5 m (8 ft 2 in) wide Euro shipping containers. Larger than UIC A.
- W11: Little used but larger than UIC B.
- W12: Slightly wider than W10 at 2.6 m (8 ft 6 in) 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 enable GB+ northwards from London via an upgraded Midland Main Line.
A strategy was adopted in 2004 to guide enhancements of loading gauges and in 2007 the Network Rail Freight Route Utilisation Strategy was published which identified a number of key routes where the loading gauge should be cleared to W10 standard and that 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: 9 ft 0 in (2.74 m) by 2.6 m (8 ft 6 in)
- W10: 9 ft 6 in (2.90 m) by 2.5 m (8 ft 2 in)
- W11: 9 ft 6 in (2.90 m) by 2.55 m (8 ft 4 in)
- W12: 9 ft 6 in (2.90 m) by 2.6 m (8 ft 6 in)
Sweden uses shapes similar to the Central European loading gauge but trains are wider. There are three main classes in use (width × height):
- Class A is 3.40 by 4.65 m (11 ft 2 in × 15 ft 3 in) (same height as UIC C).
- Class B is 3.40 by 4.30 m (11 ft 2 in × 14 ft 1 in) (similar height as UIC B).
- Class C is 3.60 by 4.80 m (11 ft 10 in × 15 ft 9 in) with a completely flat roof top.
While the Bern Gauge width of 3.15 m (10 ft 4 in) is used for 2+2 seats per row the Scandinavian 3.40 m (11 ft 2 in) width allows for 2+3 seats per row. This is used in the Regina X50 and later models on the Stockholm-Värmland relation. Similarly the newer Chinese high-speed trains use 2+3 seats per row on wider loading gauge tracks. The Swedish width is also allowed on some German railway tracks especially the relation from Berlin to the ferry lines connecting Malmö in Southern Sweden.
In the Netherlands a similar shape to the UIC C is used that rises to 4.70 m (15 ft 5 in) in height. The trains are wider allowing for 3.40 m (11 ft 2 in) width similar to Sweden. Most of the Dutch passenger trains use double-decker railcars for a maximum capacity.
Betuweroute and Channel Tunnel
- Betuweroute: 4.10 by 6.15 m (13 ft 5 in × 20 ft 2 in)
- Channel Tunnel: 4.10 by 5.60 m (13 ft 5 in × 18 ft 4 in)
The American loading gauge for freight cars on the North American rail network is generally based on standards set by the Association of American Railroads (AAR) (Mechanical Division). The most widespread standards are AAR Plate B and AAR Plate C, but higher loading gauges have been introduced on selected routes to accommodate rolling stock that make better economic use of the network, such as auto carriers and double-stack container loads.
Listed here are the maximum heights and widths for cars. However, the specification in each plate shows a car cross-section that tapers at the top and bottom, meaning that a compliant car is not permitted to fill an entire rectangle of the maximum height and width.
Plate Width Height Truck centers Comments B 10 ft 8 in 3.25 m 15 ft 2 in 4.62 m 41 ft 3 in 12.57 m For longer truck centers, the width is decreased according to graph AAR Plate B-1. C 10 ft 8 in 3.25 m 15 ft 6 in 4.72 m 46 ft 3 in 14.10 m For longer truck centers, the width is decreased according to graph AAR Plate C-1. D 10 ft 8 in 3.25 m 15 ft 2 in 4.62 m as with Plate B, but the car cross-section is larger at the top and a little larger at the bottom. E 10 ft 8 in 3.25 m 15 ft 9 in 4.80 m as with Plate C. F 10 ft 8 in 3.25 m 17 ft 0 in 5.18 m as with Plate C. H 20 ft 2 in 6.15 m e.g. Double Stacks. J 9 ft 11 3⁄8 in 3.03 m e.g. 89 ft (27.1 m) Long flatcars. K 10 ft 8 in 3.25 m 20 ft 2 in 6.15 m e.g., Autorack (road vehicles on trains).
Technically, Plate B is still the maximum and the circulation of Plate C is somewhat restricted, but the frequency of excess-height rolling stock, at first ~18 ft (5.5 m) piggybacks and hicube boxcars then later autoracks, airplane parts cars as well as 20 ft 2 in (6.15 m) high double-stacked containers in container well cars, means that many, but not all, lines are now designed for a higher loading gauge. The width of these extra height cars is covered by Plate C-1.
The standard North American passenger railcar is 10 ft 6 in (3.20 m) wide by 14 ft 6 in (4.42 m) high and measures 85 ft 0 in (25.91 m) over coupler faces with 59 ft 6 in (18.14 m) truck centers or 86 ft 0 in (26.21 m) over coupler faces with 60 ft 0 in (18.29 m) truck centers. In the 1940s and 1950s, the American passenger car loading gauge was increased to a 16 ft 6 in (5.03 m) height in the West to accommodate dome cars and later Superliners and other double-decker trains.
New York Subway
The New York City Subway is an amalgamation of three former constituent companies, and while all are standard gauge, inconsistencies in loading gauge prevent cars from the former BMT and IND systems from running on the lines of the former IRT system, and vice versa. This is mainly because IRT tunnels and stations are approximately 1 foot (300 mm) narrower than the others, meaning that IRT cars running on the BMT or IND lines would have gaps of over 8 inches (200 mm) between the train and some platforms, whereas BMT and IND cars would not even fit into an IRT station without hitting the platform edge. Taking this into account, all maintenance vehicles are built to IRT loading gauge so that they can be operated over the entire network, and employees are responsible for minding the gap.
Another inconsistency is the permissible train car length. Cars in the former IRT system can be as long as 51 feet (15.54 m); cars in the former BMT and IND can be longer: on the Canarsie, Jamaica, and Myrtle Avenue lines the cars are limited to 60 feet (18.29 m), while on the rest of the BMT and IND lines plus the Staten Island Railroad (which uses modified IND stock) the cars may be as long as 75 feet (22.86 m) long.
Korean national network has the same loading gauge as Japanese Shinkansen.
The standard gauge lines of New South Wales Government Railways (NSWGR) allowed for a width of 9 ft 6 in (2.90 m) until 1910, after a conference of the states created a new standard of 10 ft 6 in (3.20 m). The narrow widths have mostly been eliminated, except, for example, at the mainline platforms at Gosford railway station and some sidings. The longest carriages are 72' 6".
The Commonwealth Railways adopted the national standard of 10 ft 6 in (3.20 m) when they were established in 1912, although no connection with New South Wales was made until 1970.
The height of the NSW loading gauge just happens to allow for double decker trains in Sydney, while the Victorian loading gauge (in this populous city) is not quite tall enough to allow for double deck trains in Melbourne (except for one experimental train).
An NSW HV Composite Bogie Brake Van of 1884 was 8 ft 3.5 in (2.527 m) wide and 11 ft 5 in (3.48 m) tall.
A single deck Electric train of the 1920s was 10 ft 6 in (3.20 m) wide, with track centres widened to 12 ft 0 in (3.66 m) to suit. With metrication in 1973, track centres of new work were widened to 13 ft 1.5 in (4.001 m)
A double deck Electric Tangara train of the 2000s was 3000mm wide. Track centres from Penrith railway station to Mount Victoria railway station and Gosford and Wyong have been gradually widened to suit.
- The smallest loading gauge for a railway of the 1,676 mm (5 ft 6 in) gauge track is Delhi Metro. Which is 3,250 mm (10 ft 8 in) wide and 4,140 mm (13 ft 7 in) high.
- Indian Railways (including Pakistan Railways) also 1,676 mm (5 ft 6 in) gauge track have very large loading gauge. 3,660 mm (12 ft 0 in) wide and 5,300 mm (17 ft 5 in) high for passenger traffic.
- The Russian (including Finnish and ex-Soviet) loading gauges are also very large. Same loading gauge as the Indian (including Pakistan), 3,660 mm (12 ft 0 in) wide and 5,300 mm (17 ft 5 in) high for passenger traffic, on the 1,520 mm (4 ft 11 5⁄6 in) gauge track compare the 1,676 mm (5 ft 6 in) gauge track.
- In India and Pakistan, 3,250 mm (10 ft 8 in) wide and 7,150 mm (23 ft 5 in) high on the freight only lines, and 3,250 mm (10 ft 8 in) wide and 6,150 mm (20 ft 2 in) high on the passenger lines.
- In Finland, Russia and Kazakhstan, 3,250 mm (10 ft 8 in) wide and 6,150 mm (20 ft 2 in) high.
Narrow gauge railways generally have smaller a loading gauge than standard gauge ones, and this is a major reason for cost savings rather than the railgauge itself. For example, the Lyn locomotive of the Lynton and Barnstaple Railway is 7 feet 2 inches (2.18 m) wide. By comparison, several standard gauge 73 class locomotives of the NSWR, which are 9 feet 3 inches (2.82 m) wide, have been converted for use on 610 mm (2 ft) cane tramways, where there are no narrow bridges, tunnels or track centres to cause trouble. The 6E1 locomotive of the 1,067 mm (3 ft 6 in) South African Railways are 9 feet 6 inches (2.9 m) wide.
A large numbers of railways using the 762 mm (2 ft 6 in) gauge used the same rolling stock plans which were 7 ft 0 in (2.13 m) wide.
Japanese national network operated by Japan Railways Group employs narrow gauge 1,067 mm (3 ft 6 in) and has maximum width of 3,000 mm (9 ft 10 in) and maximum height of 4,100 mm (13 ft 5 in); however, a number JR lines were constructed as private railways prior to nationalisation in the early 20th century, and feature loading gauges smaller than the standard. These include the Chūō Main Line west of Takao, the Minobu Line, and the Yosan Main Line west of Kan'onji (3,900 mm (12 ft 10 in) height). Nevertheless, advances in pantograph technology have largely eliminated the need for separate rolling stock in these areas.
There are many private railway companies in Japan and the loading gauge is different for each company.
NZR uses 1,067 mm (3 ft 6 in) gauge.
- width brakevan mirrors 8' 7.75" 
- width brakevan 7' 0.125"
- height brakevan 11' 2"
South African national network employs 1,067 mm (3 ft 6 in) gauge and has maximum width of 3,048 mm (10 ft) and maximum height of 3,962 mm (13 ft).
- gauge 597 mm (1 ft 11 1⁄2 in)
- width (brakevan mirrors) 6' 10" 
- width (brakevan body) 6' 0"
- height 5' 7.5"
- gauge 762 mm (2 ft 6 in)
- minimun radius 132'
- width 7' 0" see Everard Calthrop
The structure gauge, which is the lowest and narrowest bridge or tunnel complements the loading gauge which is the tallest and widest vehicle. There is a gap between the two and some allowance needs to be made for the dynamic movement of the vehicles.
Janes World Railways yearbook contains many though not all loading gauge diagrams.
- ^ "Glossary". Network Rail. http://www.networkrail.co.uk/aspx/2232.aspx. Retrieved 2009-05-15.
- ^ a b c d "European Loading Gauges". Modern Railways. April 1992. http://www.crowsnest.co.uk/gauge.htm.
- ^ "UIC A dimensions". http://www.btinternet.com/~joyce.whitchurch/gauges/uica.gif. Retrieved 2009-05-18.
- ^ "UIC B dimensions". http://www.btinternet.com/~joyce.whitchurch/gauges/uicb.gif. Retrieved 2009-05-18.
- ^ "UIC C dimensions". http://www.btinternet.com/~joyce.whitchurch/gauges/uicc.gif. Retrieved 2009-05-18.
- ^ TSI Rolling Stock (2002/735/EC), Commission of the European Communities, 12 September 2002
- ^ a b c d Mike Smith (2003). "Track Gauge & Loading Gauge". http://myweb.tiscali.co.uk/gansg/2-track/02track3.htm.
- ^ a b c d e f "Leaflet 506 - Rules governing application of the enlarged GA, GB, GB1, GB2, GC and GI3 gauges". http://www.uic.org/etf/codex/codex-detail.php?langue_fiche=E&codeFiche=506. Retrieved 2009-05-27.
- ^ "Freight Opportunities Stage 2 Part 3 – Available Space Assessment – ISO Container Routes". Rail and Safety Standards Board. September 2007. 7481- LR- 009 issue 1. http://www.rssb.co.uk/SiteCollectionDocuments/pdf/reports/research/T727_rpt_final_part3.pdf. "(2 Definitions)‘W’ Gauge. A set of static gauges that defines the physical size of freight vehicles. [...] (3 Methodology) It was assumed that the container / wagon combinations under consideration already conform to the dimensions set out in the lower sector structure gauge. Therefore, only structural clearances above 1100mm above rail level were assessed."
- ^ "GE/GN8573". http://www.rgsonline.co.uk/Railway_Group_Standards/Infrastructure/Guidance%20Notes/GEGN8573%20Iss%202.pdf. Retrieved 2009-05-15.
- ^ "Business Plan 2004 - Network Capability". Network Rail. http://www.networkrail.co.uk/documents/3150_2004BusinessPlanNetworkCapability.pdf. Retrieved 2009-05-15.
- ^ a b c "Felixstowe South reconfiguration inspector's report". Department for Transport. http://www.dft.gov.uk/pgr/shippingports/ports/ir/felixstowesouth/felixstowesouthreconfigurati4953?page=14. Retrieved 2009-05-15. [dead link]
- ^ a b c "TEN PROPOSED ENHANCEMENT SCHEMES IN SCOTLAND". Freight on rail. http://www.freightonrail.org.uk/HotTopicsTenProposedEnhancementsScotland.htm. Retrieved 2009-05-17.
- ^ "Standard Shipping Containers". Container container. http://www.containercontainer.com/about_containers.aspx. Retrieved 2009-05-18.
- ^ a b "British and ContinentalRailway Loading Gauges". Joyce's World of Transport Eclectica. http://www.btinternet.com/~joyce.whitchurch/gauges/text.htm. Retrieved 2009-05-18.
- ^ "24 November 2006 Freight RUS Consultation Response National RUS". Central Railways. http://www.central-railway.co.uk/resources/cr_FreightConsultation2006.pdf. Retrieved 2009-05-17.
- ^ a b "Freight RUS". http://www.networkrail.co.uk/browse%20documents/rus%20documents/route%20utilisation%20strategies/freight/freight%20rus.pdf.
- ^ "Strategic Freight Network: The Longer-Term Vision". Department for Transport. http://www.dft.gov.uk/pgr/rail/strategyfinance/strategy/freightnetwork/. Retrieved 2009-05-17.
- ^ "New SRA Gauging Policy Aims to Make Best Use of Network Capability". Department for Transport. http://www.dft.gov.uk/press/releases/sra/2004/2004b/ragaugingpolicyaimstomak1394.pdf. Retrieved 2009-05-15.
- ^ a b c Car and Locomotive Cyclopedia Of American Practice
- ^ "Comparaison des gabarits UIC et nord-américains (Comparison of UIC and North American Gauges)". Marc Dufour. http://www.emdx.org/rail/Gabarit/index.html. Retrieved 2009-10-16.
- ^ April 2001 Official Railway Equipment Register.
- ^ 89 ft (27.1 m) Flat car[dead link]
- ^ Autorack[dead link]
- ^ Guide to Railcars
- ^ a b c d Hiroshi Kubota (1997-02-13) (in Japanese). Railway Engineering Handbook. Grand Prix publishing. pp. 148. ISBN 4-87687-163-9.
- ^ New Zealand Railway Freight Rolling Stock Vol 1 Template:IBSN
- ^ Festiniog Railway Volumn Two by James Boyd p365
- EU Directive 2002/732/EC - High Speed Rail Rolling Stock Standards
- Berne and all that (1992 diagram of European loading gauges) at crowsnest.com (Diagrams do not show)
- AAR "plate" loading gauge diagrams compared to UIC (pdf & Autocad)
- Railway Loading Gauges at Joyce's World of Transport Eclectica
- Loading Gauges at The Self Site
- UIC Leaflets
- Railway industrial Clearance Association
- British Track Gauge & Loading Gauge
Railway infrastructure Permanent way Trackwork and track structures Signalling and safety Buildings
Wikimedia Foundation. 2010.
Look at other dictionaries:
loading gauge — noun 1. A suspended bar that marks how high a railway truck may be loaded 2. The maximum horizontal and vertical space that rolling stock may safely occupy above the track • • • Main Entry: ↑load … Useful english dictionary
loading gauge — noun the maximum permitted height and width for rolling stock on a railway … English new terms dictionary
international loading gauge (GIC) — The loading gauge upon which international railway agreements are based. A load whose dimensions fall within the limits of this gauge may move without restriction on most of the railways of Continental Western Europe. GIC is an abbreviation for… … Military dictionary
international loading gauge — tarptautinis krovinio gabaritas statusas T sritis Gynyba apibrėžtis Krovinio gabaritas pagal tarptautinius geležinkelių susitarimus. Krovinys, kuris pagal minėtą susitarimą neviršija nustatytų matmenų, gali būti vežamas be suvaržymų per daugelį… … NATO terminų aiškinamasis žodynas
Gauge — may refer to:In measurements:* American wire gauge, a measurement of diameter of a wire * Gauge (bore diameter), the diameter of a shotgun barrel * Stubs Iron Wire Gauge, which corresponds to the diameter of a hypodermic needle **See also * Sheet … Wikipedia
Gauge conversion — Change of gauge redirects here. For other uses, see Change of gauge (disambiguation). Track gauge by size … Wikipedia
Narrow gauge railway — Track gauge by size Broad gauge St … Wikipedia
Minimum gauge railway — Track gauge by size Broad gauge Sta … Wikipedia
Berne gauge — The Berne Gauge [Berne and all that, G Hafter, Modern Railways, April 1992] or Berne Convention Gauge is an informal but widely used term for the railway loading gauge considered the standard gauge in continental Europe. The term arises from the… … Wikipedia
Structure gauge — The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse. In addition the term may … Wikipedia