Double-track railway
A double-track railway usually involves running one track in each direction, compared to a single-track railway where trains in both directions share the same track.
Overview
In the earliest days of railways in the United Kingdom, most lines were built as double-track because of the difficulty of co-ordinating operations before the invention of the
In the earliest days of railways in the United States most lines were built as single-track for reasons of cost, and very inefficient timetable working systems were used to prevent head-on collisions on single lines. This improved with the development of the
Operation
Handedness
In any given country, rail traffic generally runs to one side of a double-track line, not always the same side as road traffic. Thus in Belgium, China, France (apart from the classic lines of the former German Alsace and Lorraine), Sweden (apart from Malmö and further south), Switzerland, Italy and Portugal for example, the railways use left-hand running, while the roads use right-hand running. However, there are many exceptions:
- heavy railnetwork runs on the left.
- In Finland, rail traffic is mainly RHT, with the exception of the Ring Rail Line and the separate commuter rail tracks to Kerava and Leppävaara in Helsinki area which use LHT.
- In Switzerland, the Lausanne Metroand railways in the Germany border area, as well as all tram systems, use RHT.
- In countries such as Indonesia, it is the reverse (right-hand running for railways and left-hand running for roads).
- In Spain, where rails are RHT, metro systems in Bilbao use LHT.[1]
- In Sweden, the tram systems in Gothenburg (except for Angered station and stations with island platforms), Norrköping and Stockholm (except the Alvik – Alleparken section) are RHT.[2] The railroads (and the metro) use LHT in general, but in Malmö they use RHT due to the connection to Denmark.
- In Ukraine, some sections of Kryvyi Rih Metrotram use LHT due to tramcars having doors only on right side, which makes it impossible to use RHT at stations with island platforms.[3]
- On the pre-1918 French-German border, for example, flyovers were provided so that trains moving on the left in France end up on the right in Germany and vice versa.
- In the United States, three
Locomotive design
Handedness of traffic can affect locomotive design. For the driver, visibility is usually good from both sides of the driving cab, so the choice of which side the driver should sit less important. For example, the French SNCF Class BB 7200 is designed to use the left-hand track and therefore uses LHD. When the design was modified for use in the Netherlands as NS Class 1600, the driving cab was not completely redesigned, keeping the driver on the left even though trains use the right-hand track in the Netherlands.[5] Generally, the left/right principle in a country is followed mostly on double track. On steam trains, the steam boiler often obscured some of the view, so the driver was preferably placed nearest to the side of the railway, so that it was easier to see the signals. On single track, when trains meet, the train that does not stop often uses the straight path in the turnout, which can be left or right.[6]
Bi-directional running
Double-track railways, especially older ones, may use each track exclusively in one direction. This arrangement simplifies the signalling systems, especially where the signalling is mechanical (e.g. semaphore signals).
Where the signals and
Crossing loops
Most crossing loops are not regarded as double-track even though they consist of multiple tracks. If the crossing loop is long enough to hold several trains, and to allow opposing trains to cross without slowing down or stopping, then that may be regarded as double-track. A more modern British term for such a layout is an extended loop.
Track centres
The distance between the tracks' centres makes a difference in cost and performance of a double-track line. The track centres can be as closely spaced and as cheap as possible, but maintenance must be done on the side. Signals for bi-directional working cannot be mounted between the tracks, so they must be mounted on the 'wrong' side of the line or on expensive
Increasing the width of track centres of 6 metres (20 ft) or more makes it much easier to mount signals and overhead wiring structures. Very widely spaced centres at major bridges can have military value.[clarification needed] It also makes it harder for rogue ships and barges to knock out both bridges in the same accident.
Railway lines in desert areas affected by sand dunes are sometimes built with the two tracks separated, so that if one is covered by sand, the other(s) are still serviceable.
If the standard track centre is changed, it can take a very long time for most or all tracks to be brought into line.
Accidents
On British lines, the space between the two running rails of a single railway track is called the "four foot" (owing to it being 'four foot something' in width), while the space between the different tracks is called the "six foot". It is not safe to stand in the gap between the tracks when trains pass by on both lines, as happened in the Bere Ferrers accident of 1917.
- Narrow track centres on the Liverpool and Manchester Railway contributed to a fatal accident on opening day.
- A US naval scientist and submarine pioneer, Captain Jacques, was killed getting out of the wrong side of a train at Hadley Wood in 1916.[8]
- Narrow track centres contribute to "Second Train Coming" accidents at level crossings since it is harder to see the second train – for example, the accident at Elsenham level crossing in 2005.
Temporary single track
When one track of a double-track railway is out of service for maintenance or a train breaks down, all trains may be concentrated on the one usable track. There may be bi-directional signalling and suitable crossovers to enable trains to move onto the other track expeditiously (such as the Channel Tunnel), or there may be some kind of manual safeworking to control trains on what is now a section of single track. See single-line working.
Accidents can occur if the temporary safeworking system is not implemented properly, as in:
- Brühl train disaster, Germany – 2000.
- Zoufftgen rail crash, France – 2006
Out-of-gauge trains
From time to time, railways are asked to transport exceptional loads such as massive electrical transformers that are too tall, too wide or too heavy to operate normally. Special measures must be carefully taken to plan successful and safe operation of out-of-gauge trains. For example, adjacent tracks of a double line might have to be shut down to avoid collisions with trains on those adjacent tracks.
Passing lanes
These are a form of crossing loop, but are long enough to allow trains approaching each other from opposite directions on single-track lines to cross (or pass) each other without reducing speed. In order for passing lanes to operate safely and effectively, trains must be timetabled so that they arrive at and enter the loop with close time tolerances, otherwise they will need to slow or even be brought to a complete stop to allow the oncoming train to pass. They are suited to lines with light to moderate traffic.
An example of where passing lanes have been installed in order to improve travel times and increase line capacity is the 160-kilometre (100-mile) section of the
. This was built as a single track line in stages between 1878 and 1881, and was partially duplicated between 2005 and 2010 by the construction of four passing lanes each 6 km (4 mi) long. In this instance, this was accomplished by extending pre-existing crossing loops of either 900 metres (3,000 ft) or 1,500 metres (4,900 ft) in length.Construction
Duplication
The process of expanding a single track to double track is called duplication or doubling, unless the expansion is to restore what was previously double track, in which case it is called redoubling.
The strongest evidence that a line was built as single-track and duplicated at a later date consists of major structures such as bridges and tunnels that are twinned. One example is the twin Slade tunnels on the
Tunnel duplication
Tunnels are confined spaces and are difficult to duplicate while trains keep on running. Generally they are duplicated by building a second tunnel. An exception is the Hoosac Tunnel, which was duplicated by enlarging the bore.
Carried-out provision for duplication
To reduce initial costs of a line that is certain to see heavy traffic in the future, a line may be built as single-track but with
The former
Also:
- Smardale Gill viaduct.
- Westerham line.
- The Menangle Bridge was single track (1863) but built for double track (1890s). A second track was laid temporarily to allow testing both tracks at once.[9]
- The Long Island Rail Road's Ronkonkoma Branch was originally single track for most of its length, but land for a double track was purchased as part of a project to electrify part of the line in the 1980s.[10] A double track was laid along the rest of the segment in 2018.[11]
Never-used provision for duplication
Some lines are built as single-track with provision for duplication, but the duplication is never carried out. Examples are:
- Swanage Railway
- Bluebell Railway: Horsted Keynes to Culver Junction (Lewes).
- Keighley and Worth Valley Railway– including bridge and tunnels and a deviation.
- Westerham in Kent.
- Mid-Wales Railway (parts).
- Neath and Brecon Railway
- Monkerei Tunnel in New South Wales – double track size at summit reduces fume problem in tunnel.
- Golgotha Tunnel near Eythorne on the East Kent Light Railway was only partly excavated for the second track.
- Skitube Alpine Railway – A provision for a second 300-metre-long passing loop has been made inside the tunnel.
- New Jezreel Valley railway – Planned as a double-tracked line, but only a single track has been constructed due to budgetary issues.
- Linha do Leste and Linha do Alentejo in Portugal. The embankments in all bridges were built to double track but the second one was never installed.
- West Coast Line (Sweden). The line through Varberg is single track but prepared for double track with long enough bridges over the track. The national traffic administration (and predecessor) has since 1980 planned to build the double track, but couldn't for reason of noise rules applying to reconstructions. A new tunnel with a station was considered too expensive but is in the time plan now.[12]
Singling
When the capacity of a double-track railway is in excess of requirements, the two tracks may be reduced to one, in order to reduce maintenance costs and property taxes. In some countries this is called singling. Notable examples of this in the United Kingdom occurred on the Oxford–Worcester–Hereford, Princes Risborough–Banbury and Salisbury–Exeter main lines during the 1970s and 1980s. In all these cases, increases in traffic from the late 1990s have led to the partial reinstatement of double track. In New Zealand the
In New South Wales, Australia, the Main Western Railway between Wallerawang and Tarana, and between Gresham and Newbridge were singled in the 1990s. A new passing loop was opened on part of the closed track at Rydal in the Wallerawang–Tarana section during 2019.[13]
Tunnel singling
A double-track tunnel with restricted clearances is sometimes singled to form a single track tunnel with more generous clearances, such as the
As part of the
was converted from double- to single-track to provide additional clearance through tunnels and under bridges for trains travelling at up to 160 km/h (99 mph).A similar process can be followed on narrow bridges (like the Boyne Viaduct, a bridge just north of Drogheda railway station in Ireland).
The bridge over the
Other tunnel singling
- Hoosac Tunnel, Pan Am Railways, Massachusetts, US.[14]
- Old Main Line Subdivision, B&O, Maryland, US. Entire 58 miles (93 km) subdivision was single-tracked to utilize higher clearances of the 9 tunnels on the line.[15]
- Whitehall Tunnel, B&O, Pennsylvania, US.
Wartime doubling
Railways that become especially busy in wartime and are duplicated, especially in World War I, may revert to single track when peace returns and the extra capacity is no longer required. The Flanders campaign saw duplication of the Hazebrouck–Ypres line, amongst other works.
Triple track
Severe gradients can make the
In Melbourne and Brisbane several double track lines have a third track signalled in both directions, so that two tracks are available in the peak direction during rush hours.
Triple track is used in some parts of the
The Union Pacific Railroad mainline through Nebraska has a 108-mile (174 km) stretch of triple track between
Portions of the
India, through its state-owned Indian Railways, has initiated the construction of a third track between Jhansi and Nagpur via Bhopal (approximately 590 kilometres (370 mi)) for reducing the traffic load and delays in passenger train arrivals.[18] The construction between Bina and Bhopal[19] and between Itarsi and Budhni had been completed by April 2020.[20]
Dual gauge
The Melbourne to Albury railway originally consisted of separate 1,600 mm (5 ft 3 in) gauge and 1,435 mm (4 ft 8+1⁄2 in) gauge single track lines, but when traffic on the broad gauge declined, the lines were converted to bi-directional double track 1,435 mm (4 ft 8+1⁄2 in) gauge lines.
Quadruple track
Quadruple track consists of four parallel tracks. On a quad-track line, faster trains can overtake slower ones. Quadruple track is mostly used when there are "local" trains that stop often (or slow freight trains), and also faster inter-city or high-speed "express" trains. It can also be used in
The most notable example of quadruple track in the United States, and perhaps the only four-track section of mainline therein, was the
Outside the United States the Chūō Main Line is an example of a modern, heavily utilized urban quadruple track railway.
Quadruple track is used in rapid transit systems as well: throughout the
Oddities
Non-parallel double track
The two tracks of a double-track railway do not have to follow the same alignment if the terrain is difficult. At Frampton, New South Wales, Australia, the uphill track follows something of a horseshoe curve at 1 in 75 gradient, while the shorter downhill track follows the original single track at 1 in 40 grades.
A similar arrangement to Frampton could not be adopted between
Between Junee and Marinna, New South Wales, Australia the two tracks are at different levels, with the original southbound and downhill track following ground level with a steep gradient, while the newer northbound and uphill track has a gentler gradient at the cost of more cut and fill.
At the Bethungra Spiral, Australia, the downhill track follows the original short and steep alignment, while the uphill track follows a longer, more easily graded alignment including a spiral.
At Saunderton, England, what became the London-to-Birmingham main line of the Great Western Railway in 1909 was initially part of a single-track branch line from Maidenhead. Down trains follow the route of the old branch line, while up trains follow a more gently graded new construction through a tunnel. This scheme avoided the cost of a new double-track tunnel.
Directional running
Directional running is two separate lines operationally combined to act as a double-track line by converting each line to unidirectional traffic. An example is in central
A similar example exists in the
In other cases, where the shared lines already run in close proximity, the two companies may share facilities. In
An unusual example used to exist on the
Mixing double and single track
Because double and single track may use different signalling systems, it may be awkward and confusing to mix double and single track too often. For example, intermediate mechanical signal boxes on a double-track line can be closed during periods of light traffic, but this cannot be done if there is a single-line section in between. This problem is less serious with electrical signalling such as Centralized traffic control.
References
- ^ Moya, Aurora. "Metro de Madrid, 1919–1989. Setenta años de historia", Chapter 1
- ISBN 978-1-85414-180-4.
- ^ Vril (October 13, 2013). "Криворожский скоростной трамвай". Archived from the original on December 13, 2021. Retrieved June 26, 2018 – via YouTube.
- ^ "Ask Geoffrey". WTTW. October 9, 2013. Retrieved March 17, 2020.
- ISBN 9060132467.
- ISBN 3280014239.
- ^ "London North Eastern Sectional Appendix" (PDF). windows.net. March 2023. Retrieved May 14, 2023.
- ^ "Pioneer of Submarines". The Argus. Melbourne. November 29, 1916. p. 8. Retrieved June 30, 2011.
- ^ "Opening of the Railway to Picton". The Sydney Morning Herald. National Library of Australia. July 21, 1863. p. 8. Retrieved September 9, 2012.
- ^ "Long Island Rail Road Double Track Project" (PDF). mta.info. Metropolitan Transportation Authority. February 2013. Archived from the original (PDF) on August 26, 2014. Retrieved April 10, 2015.
- ^ "LIRR Opens Ronkonkoma Branch Double Track". MTA. September 21, 2018. Archived from the original on September 22, 2018. Retrieved September 22, 2018.
- ^ "Varbergstunneln, Västkustbanan, Varberg–Hamra". Archived from the original on March 22, 2019. Retrieved December 12, 2018.
- ^ "Two passing loops to cut train delays on the western rail line". Central Western Daily. June 14, 2018. Retrieved October 16, 2020.
- OCLC 52695896.
- ISBN 0-934118-17-5.
- ^ "Hunter Valley Rail Freight Corridor". Railway Technology. Retrieved September 30, 2018.
- ^ Canadian Trackside Guide (40 ed.). Ottawa: Bytown Railway Society. 2022.
- ^ Ranjan, Abhinav (August 25, 2016). "Government approves Rs 27,000 cr railway lines, national highways projects". www.indiatvnews.com. Retrieved April 24, 2020.
- ^ Singh, Ramendra (January 12, 2020). "Work on third railway line hits Subhash Nagar RoB hurdle". The Times of India. Retrieved April 24, 2020.
- ^ "Habibganj-Itarsi third track work begins". The Times of India. June 11, 2015. Retrieved April 24, 2020.
- ^ "Eureka County, Yucca Mountain Existing Transportation Corridor Study". Eureka County – Yucca Mountain Project. 2005. Retrieved May 8, 2010.
- ISBN 0-929591-81-X.
- ^ "Eureka County, Yucca Mountain Existing Transportation Corridor Study". Eureka County – Yucca Mountain Project. 2005. Retrieved May 8, 2010.
- ^ "CN, CPR TO SHARE U.S., CANADA ROUTES". American Shipper. Freightwaves Inc. July 21, 2000.
- ^ Trains. November 2009. p. 46.
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(help)[title missing] - ISBN 1-85414-276-3.
External links
- Media related to Double-track railway lines at Wikimedia Commons