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A dual-gauge or mixed-gauge railway has railway track that allows trains of different gauges to use the same track. Generally, a dual-gauge railway consists of three rails, rather than the standard two rails. The two outer rails give the wider gauge, while one of the outer rails and the inner rail give a narrower gauge - one of the three rails is common to all traffic. This configuration is not to be confused with the electric third rail.
In railways, the most important specification is that of gauge, the distance between the inner surfaces of the heads of the travel rails (see diagram above). Both track and wheels bogies must be built to the same gauge; unless the two fit together within a tolerance of 13 mm (0.51 in) on the track, the train will either fall off the track or it will be impossible to go through switches or cross overs. For instance, the Hong Kong MTR 1,432 mm (4 ft 8 3⁄8 in)-gauge EMU's may run on KCR 1,435 mm (4 ft 8 1⁄2 in)-gauge rails, with a locomotive or a KCR EMU pulling due to different electrify voltages. A problem arises when different gauges meet one another, a situation known as a break of gauge. Either the track or the train must be built to handle different gauges, or passengers and freight must be taken off one train and loaded on to the next.
In allowing railway tracks of different gauges to share the same alignment, costs can be reduced, especially where there are bridges and tunnels. Dual gauge can replace two separate tracks, having two rails each, with one track with three rails. This allows one rail fewer for the stretch of the dual gauge line, but there are complications and costs that may offset the savings.
One issue is points (US: switches). Complicated arrangements are necessary to ensure traffic of both gauges can safely utilise points. Signalling may also be complicated somewhat, as all three rails must be connected to track circuits or mechanical interlocking arrangements. Mixed gauge is simpler to signal with electric signals than with mechanical signals. Since rails wear very slowly, the extra tonnage on the common rail is generally not a problem.
Dual-gauge turnouts will be complicated, expensive, and suitable for low speeds only.
For dual-gauge track to be achievable using three rails, the difference between the gauges needs to be at least as wide as the foot of the rail, otherwise there is no room for the rail fastening hardware (spikes, clips, and the like). Thus standard gauge (1,435 mm (4 ft 8 1⁄2 in)) and Indian gauge 1,676 mm (5 ft 6 in) can be dual gauged without problem, as are 914 mm (3 ft) and 1,067 mm (3 ft 6 in) (Cape gauge), or 1,524 mm (5 ft) and 1,829 mm (6 ft) , while 1,435 mm (4 ft 8 1⁄2 in) and 1,600 mm (5 ft 3 in) (Irish gauge) can also be dual-gauged, albeit with lighter narrow footed rails, as in Victoria, Australia. On the other hand, metre gauge 1,000 mm (3 ft 3 3⁄8 in) and cape gauge 1,067 mm (3 ft 6 in) as in Africa, or 1,000 mm (3 ft 3 3⁄8 in) and 3 ft (914 mm), as in South America, are too close to be combined into three-rail dual gauge, as are 1,435 mm (4 ft 8 1⁄2 in) and 1,524 mm (5 ft) , or 1,524 mm (5 ft) and 1,676 mm (5 ft 6 in), as in Afghanistan, Central Asia, northern-, central- and eastern Europe, North America, Iran, and China. This last combination is of particular historical interest, as it was of strategic significance during World War II.
If three-rail dual gauge is impossible (e.g. between 1,435 mm (4 ft 8 1⁄2 in) and 1,524 mm (5 ft) ), four-rail dual gauge has to be used.
The complications and difficulties outlined show how important it is to ensure that railway gauges are standardised in the first place, if at all possible. If a railway operator seeks to convert from one gauge to another, then it helps if a dual-gauge intermediate step can be done (this has often been practised in the past).
If the gauge is to be reduced, then the sleepers can continue to protrude from the side of the rails. If the gauge is to be increased, then the sleepers used for narrow gauge may be too short, and some at least of these 'short' sleepers will have to be replaced with longer ones. Alternatively the rails may be too light for the loads imposed by broader-gauge railcars. Such potential problems can rule out dual-gauge as a feasible option. Another issue is affixing the rails to the sleepers (spikes, nails or bolts are used). If existing sleepers are wooden, extra holes can be drilled without problems. If the existing sleepers are concrete, then drilling extra holes is impractical, and the whole sleeper has to be replaced, unless extra boltholes are already allowed for.
The embankment could need widening too. It is possible that viaducts and tunnels are too narrow and too low. This could cost a lot and need the closing of the line for a year or two.
During the conversion of the Melbourne-Adelaide railway in Australia from 5 ft 3 in (1,600 mm) to 4 ft 8 1⁄2 in (1,435 mm), dual gauge with heavy rails was not possible as the rail footings were too wide. A special gauge-convertible sleeper with a reversible chair for the Pandrol clip allowed a two-week conversion process.
In the Adelaide metropolitan area, broad-gauge timber sleepers are being replaced with gauge-convertible concrete sleepers. On June 5, 2008, the South Australian Government announced that the Metropolitan Network would be converted to standard gauge (1435 mm) in 2012.[1]
Dual-gauge lines in Java were regauged from 4 ft 8 1⁄2 in (1,435 mm) to 3 ft 6 in (1,067 mm) (Cape gauge) during the Japanese administration in 1942-1943. Regauging occurred only on the relatively short Brumbung-Kedungjati-Gundih main line and the Kedungjati-Ambarawa branch line, as the rest of the line was already dual-gauge (some only recently dual-gauged).
In Los Angeles the 3 ft 6 in (1,067 mm) Los Angeles Railway and the 4 ft 8 1⁄2 in (1,435 mm) Pacific Electric Railway (both defunct) ran on dual gauge track on some downtown streets.
In Japan, dual gauge is used when standard gauge Shinkansen (Bullet Train) lines joins the narrow-gauge (1,067 mm/3 ft 6 in) system, which is the national standard. For example, part of the Ōu line became part of the Akita Shinkansen and was upgraded to dual gauge.
In Dutch East Indies (later Indonesia), dual-gauge track was installed in 1899 between Yogyakarta and Solo. The track was owned by the Nederlandsch-Indische Spoorweg Maatschappij, a private company, which built the 4 ft 8 1⁄2 in (1,435 mm) gauge line in 1867. The third rail was installed to allow passengers and goods traveling over the 3 ft 6 in (1,067 mm) gauge Staatsspoorweg (State Railway) a direct connection without requiring transfer at both cities. Later, a separate pair of tracks were installed at the government's cost to allow greater capacity and higher speeds.
In 1940 a third rail was installed between Solo and Gundih on the line to Semarang, allowing 3 ft 6 in (1,067 mm) gauge trains to travel between Semarang, Solo and Yogyakarta (via Gambringan, on the line to Surabaya instead of via Kedungjati on the original line).
A short section of dual-gauge 3 ft 6 in (1,067 mm) and 2 ft 5 1⁄2 in (750 mm) line existed in North Sumatra on a joint line of the Deli Railway and the Aceh Tramway. This line survived in to the 1970s.
Some sugar mill railways in Java have dual-gauge sections.
In Vietnam, there is dual gauge (1,000 mm/3 ft 3 3⁄8 in metre and 1,435 mm/4 ft 8 1⁄2 in standard) between Hanoi and the Chinese border.[5]
In the Czech Republic, there is dual gauge (1,435 mm/4 ft 8 1⁄2 in and 760 mm/2 ft 5 7⁄8 in) track near Jindřichův Hradec. The two gauges are used by different railway companies.
In Britain, the Great Western Railway was initially broad gauge, 7 ft 0 1⁄4 in (2,140 mm). After the "gauge war", it was decided to regauge the GWR. As the broad gauge was sufficiently dissimilar from standard gauge and used wooden sleepers, dual gauge was easily introduced. The Metropolitan Railway, now part of the London Underground system, started as dual gauge: its present third and fourth rails are for electricity supply, not dual gauge. A small section of broad gauge, 7 ft 0 1⁄4 in (2,140 mm) and standard gauge 1,435 mm (4 ft 8 1⁄2 in) demonstration line exists at the Great Western Society site at Didcot.
In Ireland, dual-gauge track was not used in regauging the Ulster Railway (UR). When it regauged its double-track route from 6 ft 2 in (1,880 mm) to the new Irish standard of 5 ft 3 in (1,600 mm) it performed the task in two stages. The Dublin & Drogheda Railway (D&DR) meanwhile was regauging from 5 ft 2 in (1,575 mm), too similar to the new gauge to allow dual gauge. Dual gauge was used in Derry, by the Port Authority, in an on-street network to transfer goods, on either gauge, between the city's four stations (two 3 ft /914 mm narrow gauge, two 5 ft 3 in/1,600 mm in broad gauge).
In Italy, dual-gauge track is used in the Potenza - Avigliano Lucania line, 1,435 mm (4 ft 8 1⁄2 in) and 950 mm (3 ft 1 3⁄8 in).
In France, the Chemin de Fer de la Baie de Somme is dual gauge between Noyelles-sur-Mer and Saint-Valery-sur-Somme, metre gauge laid within standard gauge, thus having four rails.
In Belgium, some sections of tram track in Brussels combined 1,000 mm (3 ft 3 3⁄8 in) metric gauge for the interurban trams with 1,435 mm (4 ft 8 1⁄2 in) standard gauge for the urban trams. Since the closure of the former, these have been replaced with standard gauge track.
In Germany, the Stuttgart tram lines were 1,000 mm (3 ft 3 3⁄8 in) gauge. In the 1970s it was decided to convert the tram system to a modern Stadtbahn and regauge it to standard gauge to increase capacity. Inner-city tunnels replacing street-level sections in busy streets were built with a cross-section suitable for standard-gauge cars. After the conversion started in 1981 with the commissioning of the first three class DT-8 Stadtbahn cars, the tunnels and all other sections used by multiple lines were fitted with 1,435 mm (4 ft 8 1⁄2 in)/1,000 mm (3 ft 3 3⁄8 in) dual-gauge track, to allow both old-style trams and new Stadtbahn cars to share those sections while lines were converted one by one over the next decades. In 2006, conversion of line 15 (the last line to be converted) is under way and was completed in 2008, although some sections will retain their dual-gauge track indefinitely as a courtesy to the tram museum of Stuttgart, which will operate old 1,000 mm (3 ft 3 3⁄8 in) gauge trams on weekends and special occasions.
Also in Germany, in Krefeld on Ostwall the tram lines are dual-gauge track, to allow both standard 1,435 mm (4 ft 8 1⁄2 in) Rheinbahn U76 Stadtbahn cars to share this section with Krefeld's metre 1,000 mm (3 ft 3 3⁄8 in) gauge. At the north end of the street at the junction with Rheinstraße, Rheinbahn trams reverse, so the standard gauge ends, while the metre gauge lines continue. The dual-gauge track continues along Oppumer Straße in front of Krefeld Hauptbahnhof (Main Rail Station), where at both ends of this street, the metre 1,000 mm (3 ft 3 3⁄8 in) and standard 1,435 mm (4 ft 8 1⁄2 in) tracks diverge.
In Switzerland dual gauge track (1,435 mm/4 ft 8 1⁄2 in standard and 1,000 mm/3 ft 3 3⁄8 in metric) is used in (Lucerne and Interlaken) stations at both ends of the Brünigbahn and on the RhB between Chur and Domat Ems (see first illustration of this article), among other places.
In Sweden and Finland, there is 2 km of dual gauge, 1,435 mm (4 ft 8 1⁄2 in) and 1,524 mm (5 ft) , between Haparanda and Tornio across the bridges over the border. At each end of the dual-gauge section there are yards with standard and Finnish gauge areas to allow for trans-shipment. The four-rail method is used because the gauges are close together. The bridge structure needs to be wider than normal to allow for the offset from the centreline by each gauge. At the Tornio yard is a Rafil gauge changer. Similar arrangements exist on the approach to Kaliningrad, where 1,435 mm (4 ft 8 1⁄2 in) track penetrates from the Polish border with some dual gauge stretches.
In Spain, there is dual gauge in the AVE line from Zaragoza to Huesca, usable for both 1,435 mm (4 ft 8 1⁄2 in) standard gauge high speed trains and 1,668 mm (5 ft 5 2⁄3 in) Iberian gauge Spanish trains. In 2009, Adif called for tenders for the installation of a third rail for standard gauge trains on the 22 km (14 mi) between Castellbisbal and the Can Tunis freight terminal in Barcelona.[6]
In Western Australia there is a double-track dual-gauge (3 ft 6 in/1,067 mm & 4 ft 8 1⁄2 in/1,435 mm) main line from East Perth to Northam, about 120 km. Dual-gauge track is also used from the triangle at Woodbridge to Cockburn Junction, then to Kwinana on one branch, and North Fremantle on the other.
In Brisbane, Australia, shorter stretches of dual-gauge track (3 ft 6 in/1,067 mm & 4 ft 8 1⁄2 in/1,435 mm) exist between the rail freight yards at Acacia Ridge and the Port of Brisbane, for freight trains. A dual-gauge line branches off at Park Road Station to run alongside the electric suburban narrow gauge Citytrain line over the Merivale Bridge into Platform 1 at Roma Street Station. This is used by standard-gauge interstate CountryLink XPT services to Sydney.
In Australia, the new railway line between Perth and Northam was being planned in the 1960s. The improved alignment was originally intended to have separate standard gauge and narrow gauge tracks running parallel, with crossing loops at intervals. However, the capacity of each of these lines would have been poor. By adopting double-track dual-gauge throughout, the line capacity was greatly increased, at only the relatively small extra cost of providing a third rail was needed for dual gauge.
There have been a few instances of triple-gauge break-of-gauge stations.
| Area | Gauge 1 | Gauge 2 | Gauge 3 | Note |
|---|---|---|---|---|
| Port Pirie, South Australia | 1,067 mm (3 ft 6 in) | 1,435 mm (4 ft 8 1⁄2 in) | 1,600 mm (5 ft 3 in) | 1938–1970, . |
| Gladstone, South Australia | 1,067 mm (3 ft 6 in) | 1,435 mm (4 ft 8 1⁄2 in) | 1,600 mm (5 ft 3 in) | 1968-1980s |
| Peterborough, South Australia | 1,067 mm (3 ft 6 in) | 1,435 mm (4 ft 8 1⁄2 in) | 1,600 mm (5 ft 3 in) | 1968-1980s some survives in the Steamtown Heritage Rail Centre |
| Latour-de-Carol, France | 1,000 mm (3 ft 3 3⁄8 in) | 1,435 mm (4 ft 8 1⁄2 in) | 1,668 mm (5 ft 5 2⁄3 in) | still in use |
| Hendaye, France | 1,000 mm (3 ft 3 3⁄8 in) | 1,435 mm (4 ft 8 1⁄2 in) | 1,668 mm (5 ft 5 2⁄3 in) | still in use |
| Växjö, Sweden | 891 mm (2 ft 11 1⁄10 in) | 1,067 mm (3 ft 6 in) | 1,435 mm (4 ft 8 1⁄2 in) | until at least 1974 |
| Montreux, Switzerland | 800 mm (2 ft 7 1⁄2 in) | 1,000 mm (3 ft 3 3⁄8 in) | 1,435 mm (4 ft 8 1⁄2 in) | still in use |
| Capolago, Switzerland | 800 mm (2 ft 7 1⁄2 in) | 1,000 mm (3 ft 3 3⁄8 in) | 1,435 mm (4 ft 8 1⁄2 in) | the metre gauge line closed in 1950 |
| Volos, Greece | 600 mm (1 ft 11 5⁄8 in) | 1,000 mm (3 ft 3 3⁄8 in) | 1,435 mm (4 ft 8 1⁄2 in) | 600 mm gauge closed on 70's, 1000 mm gauge closed on 1998 |
Because these three triple-gauge examples were yards operating at low speed, light rail could be used to space the rails closely together if required. Main line operation at high speeds is another matter.
The Niagara Falls Suspension Bridge originally carried trains of three different gauges.
The National Railway Museum (Port Adelaide) in Adelaide, Australia has the three main-line gauges and a 18 in (457 mm) gauge tourist line.
On September 9, 2004, an accident happened on a switch in Jindřichův Hradec, Czech Republic where a dual-gauge railway bifurcates. A Junák express from Plzeň to Brno derailed due to a signalling error. The standard gauge train was switched onto the narrow gauge track. The express train driver was slightly injured.
In Western Australia, the signalling system detects the gauge of the approaching trains and puts the signals to stop if the route is set for the wrong gauge.
Dual-gauge turnouts (also known as switches or points), where both gauges have a choice of routes, are quite complicated, with more moving parts than single-gauge turnouts. They impose very low speed limits. If dual-gauge points are operated and detected by electrical circuits, their reliability will be high.
Where two gauges separate (i.e. each gauge has only one route, as in the picture at right), few if any moving parts are needed.
Third-rail was proposed around 1900 as a solution for the break of gauge problems in Australia, but there was a problem with the design of turnouts due to the closeness of standard gauge and irish gauge of only 6.5 inches. After one or two decades on increasing rancour, the dual gauge option was rejected as unacceptable, especially the Brennan dual gauge switch. [7]
However, where the difference between the gauges is large, say 14.5 inches between 1,067 mm (3 ft 6 in) and 1,435 mm (4 ft 8 1⁄2 in), dual gauge is not a problem, as evidenced by 45 years of successful operation in Western Australia.
In Australia, after a brief period of support, dual gauge between 1,600 mm (5 ft 3 in) gauge and 1,435 mm (4 ft 8 1⁄2 in) gauge came to be vehemently opposed, even with the Brennan switches, mainly because of hazard of the narrow gap between the outer.
For good measure, dual gauge between 1,600 mm (5 ft 3 in) gauge and 1,067 mm (3 ft 6 in) gauge was also opposed, even though the gap is much bigger. [8]
The separate ends of dual gauge turnouts are easier to arrange if the ends are electrically operated rather than mechanically operated.
If the two gauges of a dual gauge turnout are very similar and the difference between them is small, turnouts will have many small pieces that are difficult to support and the turnout will be weak and limited in speed. Paradoxically, the larger the difference the better. The difference between the gauges should as a rule of thumb be 50 mm greater than the width of the base of the rails. The difference between standard and East European/Russian gauge is too narrow.
One way of avoiding complicated and weak dual gauge turnouts, provided there is room, is to separate the gauges and then design the yard with single gauge turnouts and dual gauge diamond crossings.[9][10] Gauge splitters assume that trains have a single gauge. Gauge splitters may be fixed, meaning they have no moving parts and are intended for low speed use, or they be power operated like ordinary turnouts.
If dual-gauge turnouts are too slow, or too difficult because the gauges are too similar, then an option is to build two separate lines, one of each gauge, side by side. This choice also depends on the amount of traffic. Dual-gauge could continue to be employed at an expensive bridge or tunnel.
Separate lines can at least share signal boxes, signallers and other major infrastructure.
Examples include:
Low level platforms are not a problem with dual gauge trains. since carriages are always higher than the platforms.
With third rails and high level platform, one gauge may be too close or too far away, depending on which side the third rail is. In Western Australia, between Midland and Perth Terminal Terminal, the problem does not in practice arise, because the standard gauge trains do not stop at the intermediate stations.
Bangladesh is tackling its break of gauge problem by adding a third rail to its broad and narrow gauge lines, so that it becomes a mainly dual-gauge system. The new Jamuna Bridge that links the east and west rail systems is four rail dual gauge so that both gauges use the same centre-line. At some stage Bangladesh may choose one gauge over the other and convert to a single gauge, but there are no immediate plans for this.
Bangladesh's neighbour to the east is also 1000 mm gauge, should the missing link ever be built.
A variation of overlapping gauge is to extend a railway of one gauge into territory that is mainly of another gauge so as to avoid transhipment of specific traffic. For example a 1524 mm gauge line from an iron ore mine in Ukraine to a steelworks in Slovakia, which now may be extended into Austria.[11]
Other methods of handling multiple gauges include:
A mini-metro in Gijon, Spain is to be both dual gauge (1,000 mm/3 ft 3 3⁄8 in and 1,668 mm/5 ft 5 2⁄3 in) and dual voltage (1500 V DC/3000 V DC).
Tillig make dual gauge model railway track.[12]
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