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Dual-gauge or mixed-gauge railway is a special configuration of railway track, allowing trains of different gauges to use the same track. Generally 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 one inner allow a narrower gauge. Thus one of the rails is common to all traffic. This configuration is not to be confused with the electric third-rail.
Reasoning
The example image shows a site in Switzerland. Due to landscape restrictions (not for reason of costs), many mountain railways had to be built for use with special narrow gear. Reduction of gear width forced to reduce gauge width, because with steam-driven engines the cylinders had to be mounted at the outside of the axles and wheels for best efficiency. Thus resulted gauges of 800 and 1000 mm. Note that, where possible, Swiss mountain railways were built in standard gauge.
As mountain railway gear is not suitable for standard lines and vice-versa, there is no need for compatibility. The three-rail lines seen on the example images connect standard railway and moutain railway near a station. They were built this way for interchange comfort. As Swiss mountain railways were immensely expensive, special constructions like three-rail turnouts hardly affected overall costs.
Configuration
For dual gauge to work with 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 1435 mm (4 ft 8½ in, standard gauge) and 1676 mm (5 ft 6 in) can be dual gauged without problem, while 1435 mm (4 ft 8½ in) and 1600 mm (5 ft 3 in, Irish gauge) can also be dual-gauged albeit with lighter narrow footed rails, as shown in Victoria, Australia (where the majority of the railways use the 1600 mm gauge). On the other hand, metre gauge (3 ft 3.4 in) and 1067 mm (3 ft 6 in) as found in Africa are too similar to work with three-rail dual gauge.
If three-rail dual gauge is impossible, four-rail dual gauge may be possible.
Configuration for Africa
1067 mm and 1000 mm gauges found in Africa are too close to allow three-rail dual gauge: four-rail dual gauge is required. With a little care, the sleepers for this dual gauge configuration can be made to support triple gauge, including standard gauge (1435 mm), at little extra cost.
An advantage of the four-rail dual gauge track is that the four rails combined to give some of the greater strength of two rails of double the weight. The allows the old rails to be reused, instead of being scrapped or used for fenceposts.
Example in Africa
2004
On 12 October 2004, a proposal was announced to develop an electrified rail link connecting Kenya, Uganda and south Sudan. Even though Kenya and Uganda use 1000 mm gauge and Sudan uses 1067 mm, the new project was proposing to use standard gauge (1435 mm). Fortunately, all three gauges can be supported by the same sleepers (railroad ties), as described above.2006
An Indian proposal surfaced to link Benin and Togo on the coast with landlocked Burkina Faso and Niger. The other adjacent state of Ghana and Nigeria use the incompatible 1067 mm gauge. With the future in mind, steel and concrete sleepers, at least between stations, can and should cater for three gauges, 1000 mm, 1067 mm and 1435 mm.Gauge conversion
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 actually 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 extra holes are impossible, and the whole sleeper has to be replaced, unless extra boltholes are already allowed for.
During the conversion of the Melbourne to Adelaide line in Australia from 5' 3" to 4' 8½, 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, in case of future gauge conversion.
During WW1 and WW2, gauge conversion occurred backwards and forwards between Europe and Russia as the fronts and national borders chopped and changed.
The dual-gauge lines in Java were regauged to narrow gauge (4' 8½" to 3' 6") during the Japanese occupation in 1942-1943. Actual regauging only occurred on the relatively short Brumbung-Kedungjati-Gundih main line and the Kedungjati-Ambarawa branch line, as the rest of the line were already dual-gauge (some only recently dual-gauged).
Cost of an example
In 2005, Pakistan Railways started work on the conversion of the 128km Mirpurkhas to Khokhrapar line from 1000 mm to 1676 mm gauge. The cost was set at Rs 1,800,000,000 (US$30,000,000), or about US$ 250,000 per km.Examples
In the Czech Republic, there is dual gauge (1435 mm and 760 mm) track near Jindřichův Hradec. Interestingly, the two gauges are used by different railway companies.
In Britain, the Great Western Railway was initially broad gauge. 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 for running new standard-gauge traffic. The Metropolitan Railway, part of the London Underground system, also started out as dual-gauge; however, its current third and fourth rails are for electricity supply, not dual gauge.
In Ireland, dual-gauge track was not used in regauging the Ulster Railway (UR). When it regauged from 1879 mm (6 ft 2 in) to the new standard of 1600 mm (5 ft 3 in), it regauged its double-track route in two halves. The Dublin & Drogheda Railway (D&DR) meanwhile was regauging from 1575 mm (5 ft 2 in), too similar to the new gauge to allow dual gauge. Dual gauge was used in Londonderry, by the Port Authority, in an on-street network to transfer goods, on either gauge, between the city's four stations (two 3 ft narrow gauge, two 5 ft 3 in broad gauge).
In Western Australia, there is a double-track dual-gauge (3' 6" & 4' 8½") 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, Queensland, shorter stretches of dual-gauge track (3' 6" & 4' 8½") 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 electric suburban narrow gauge CityTrain services over the Merivale Bridge into Platform 1 at Roma Street Station. This is used by standard-gauge interstate CountryLink XPT services to Sydney.
In Stuttgart, Germany, the tram lines were 1000 mm gauge. In the 1970s it was decided to convert the streetcar 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 1435 mm / 1000 mm dual-gauge track, to allow both old-style streetcars 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 expected to be complete around 2008, although some sections will retain their dual-gauge track indefinitely as a courtesy to the streetcar museum of Stuttgart, which will operate old 1000 mm gauge streetcars on weekends and special occations.
In Switzerland dual gauge (standard and meter) is used in the stations at both ends of the Brünigbahn (Lucerne and Interlaken), as well as on the RhB between Chur and Domat Ems (see first illustration of this article), among other places.
In Japan, dual gauge is used when the Shinkansen system, which is standard gauge, joins the narrow-gauge (1067 mm) 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' 8½" gauge line in 1867. The third track was installed to allow passengers and goods traveling over the 3' 6" 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' 6" 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' 6" and 2' 5½" (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 also have dual-gauge sections.
In Vietnam, there is dual gauge (meter and standard) between Hanoi and the Chinese border.
Triple gauge
There have been a few instances of triple-gauge break-of-gauge stations.
- Port Pirie, South Australia, 3' 6", 4' 8½", 5' 3" (1938-1970)
- Gladstone, South Australia, 3' 6", 4' 8½", 5' 3" (1970-1980s)
- Peterborough, South Australia, 3' 6", 4' 8½", 5' 3" (1970-1980s)
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.
Accidents on dual-gauge railways
On September 9, 2004, an accident happened on a switch in Jindřichův Hradec where dual-gauge railway bifurcates. An Junák express train from Plzeň to Brno derailed here because of a signalman's fault. He switched the switch to the narrow-gauge track although the express train used the standard-gauge one. Only the driver of the express train was slightly injured.
Complexity of dual-gauge switches
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), it is sometimes done without any moving parts.
Separate gauge
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.
Examples include:
- Albury, New South Wales to Melbourne, Victoria, 300 km
- As the old and original broad gauge track declines in use, it is slated for conversion to standard gauge, replacing parallel standard-gauge single track and broad-gauge double track with a double-track standard-gauge line. This will reduce delays on the standard-gauge line at crossing loops.
- Melbourne Victoria, to Geelong, Victoria, 80 km, a single standard-gauge line parallel to double-track broad gauge.
- Yogyakarta-Solo in Java, Dutch East Indies during pre-WW II days, 58 km. This had a single 3' 6" line parallelling a dual-gauge 4' 8½" and 3' 6" line.
- In 2005 a proposed standard gauge line connecting Iran with China via several broad gauge Central Asian countries will use a mixture of parallel separate lines and dual gauge.
Overlapping gauges
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.
Other methods of handling multiple gauges
Other methods of handling multiple gauges include:
- Transporter wagons or transporter trucks, which carry equipment of one gauge on the other's tracks.
- Truck exchange systems, where the railroad car is lifted and the trucks/bogies under it are swapped. This system is not suitable for four-wheel wagons.
- Adjustable gauge equipment (variable gauge axles), in which the wheel gauge can be widened or narrowed.
- Transshipment; transferring goods or people from one set of railroad cars to another.
- Containerisation.
Dual gauge dual voltage
A mini-metro in Gijon, Spain is to be both dual gauge (1000 mm/1676 mm) and dual voltage (1500 V DC/3000 V DC).
See also
- Gauntlet track
- Railroad switch (points)
- History of rail transport by country
- Rail gauge
- Rail terminology
- Rail transport
- Rail transport by country
- Break-of-gauge
- Variable gauge axles
External links
"Dual gauge"