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96-595: The electrified double track line serves as a major conduit for moving coal produced in Shanxi , Shaanxi , and Inner Mongolia to Qinhuangdao, China's largest coal-exporting seaport, from there coal is shipped to south China and other countries in Asia. The railway also passes through the municipalities of Beijing and Tianjin . Unlike most other railways in China, which are run by the state-owned China Railway Corporation ,

192-576: A single-track railway where trains in both directions share the same track. 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 telegraph . The lines also tended to be busy enough to be beyond the capacity of a single track. In the early days the Board of Trade did not consider any single-track railway line to be complete. In

288-550: 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

384-564: A broken red lens could be taken by a driver as a false 'clear' indication. It was not until scientists at Corning Glassworks perfected a shade of yellow without any tinges of green or red that yellow became the accepted colour for 'caution'. Mechanical signals are usually remotely operated by wire from a lever in a signal box, but electrical or hydraulic operation is normally used for signals that are located too distant for manual operation. On most modern railways, colour light signals have largely replaced mechanical ones. Colour light signals have

480-419: A busy commuter line might have blocks a few hundred metres long. A train is not permitted to enter a block until a signal indicates that the train may proceed, a dispatcher or signalman instructs the driver accordingly, or the driver takes possession of the appropriate token. In most cases, a train cannot enter the block until not only the block itself is clear of trains, but there is also an empty section beyond

576-423: A centralized train dispatcher's office that controls railroad interlockings and traffic flows in portions of the rail system designated as CTC territory. Train detection refers to the presence or absence of trains on a defined section of line. The most common way to determine whether a section of line is occupied is by use of a track circuit . The rails at either end of each section are electrically isolated from

672-459: A danger signal for a specific time, although this is only permitted when the signal does not protect any conflicting moves, and also when the signalman is unable to contact the next signal box to make sure the previous train has passed, for example if the telegraph wires are down. In these cases, trains must proceed at very low speed (typically 32 km/h (20 mph) or less) so that they are able to stop short of any obstruction. In most cases, this

768-416: A double line might have to be shut down to avoid collisions with trains on those adjacent tracks. 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

864-411: A driver is informed which route the train will take beyond each signal (unless only one route is possible). This is achieved by a route indicator attached to the signal. The driver uses their route knowledge, reinforced by speed restriction signs fixed at the lineside, to drive the train at the correct speed for the route to be taken. This method has the disadvantage that the driver may be unfamiliar with

960-399: A driver of an upcoming change of route. Under speed signalling , the signal aspect informs the driver at what speed they may proceed over a junction, but not necessarily the route the train will take. Speed signalling requires a far greater range of signal aspects than route signalling, but less dependence is placed on drivers' route knowledge, although the need for drivers to learn the route

1056-449: A green light with a safe condition, this was not historically the case. In the very early days of railway signalling, the first coloured lights (associated with the turned signals above) presented a white light for 'clear' and a red light for 'danger'. Green was originally used to indicate 'caution' but fell out of use when the time interval system was discontinued. A green light subsequently replaced white for 'clear', to address concerns that

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1152-526: 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 Rydal and Sodwalls on the Main Western railway line because the 1 in 75 uphill track is on the wrong side of the 1 in 40 downhill track, so both tracks follow the 1 in 75 grade. Another example is at Gunning . Between Junee and Marinna, New South Wales , Australia

1248-627: A major bottleneck. For Berlin Stadtbahn the two northern tracks are local S-Bahn and the two other for faster trains. The most notable example of quadruple track in the United States, and perhaps the only four-track section of mainline therein, was the Pennsylvania Railroad 's main corridor through the heart of Pennsylvania around the famous Horseshoe Curve . This line is now owned by Norfolk Southern. Other examples include

1344-526: A number of accidents, most notably the Armagh rail disaster . This required block signalling for all passenger railways, together with interlocking , both of which form the basis of modern signalling practice today. Similar legislation was passed by the United States around the same time. Not all blocks are controlled using fixed signals. On some single track railways in the UK, particularly those with low usage, it

1440-558: A safe manner taking this information into account. Generally, the signal remains at danger, and the driver is given verbal authority, usually by a yellow flag, to pass a signal at danger, and the presence of the train in front is explained. Where trains regularly enter occupied blocks, such as stations where coupling takes place, a subsidiary signal, sometimes known as a "calling on" signal, is provided for these movements, otherwise they are accomplished through train orders. The invention of train detection systems such as track circuits allowed

1536-449: A scheduled time, during which they have 'possession' and no other train may use the same section. When trains run in opposite directions on a single-track railway, meeting points ("meets") are scheduled, at which each train must wait for the other at a passing place. Neither train is permitted to move before the other has arrived. In the US, the display of two green flags (green lights at night)

1632-596: A second tunnel. An exception is the Hoosac Tunnel , which was duplicated by enlarging the bore. 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 earthworks and structures designed for ready duplication. An example is the Strathfield to Hamilton line in New South Wales , which was constructed as mainly single-track in

1728-406: A signal box. When a train passed into a block, a signalman would protect that block by setting its signal to 'danger'. When an 'all clear' message was received, the signalman would move the signal into the 'clear' position. The absolute block system came into use gradually during the 1850s and 1860s and became mandatory in the United Kingdom after Parliament passed legislation in 1889 following

1824-456: A speed that they can stop safely should an obstacle come into view. This allows improved efficiency in some situations and is mostly used in the USA. In most countries it is restricted to freight trains only, and it may be restricted depending on the level of visibility. Permissive block working may also be used in an emergency, either when a driver is unable to contact a signalman after being held at

1920-439: A station or signal box to send a message (usually a specific number of rings on a bell ) to confirm that a train had passed and that a specific block was clear. This was called the " absolute block system ". Fixed mechanical signals began to replace hand signals from the 1830s. These were originally worked locally, but it later became normal practice to operate all the signals on a particular block with levers grouped together in

2016-565: 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 New York City Subway and on the Norristown High-Speed Line to add supplemental rush-hour services. The center track, which serves express trains, is signalled in both directions to allow two tracks to be used in the peak direction during rush hours;

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2112-412: A third track was opened between Whittingham and Branxton in 2011 and Branxton to Maitland in 2012 to equalize the headway in both directions for heavy coal traffic. Triple track could be a compromise between double-track and quad-track ; such a system was proposed south of Stockholm Central Station , but was cancelled in favor of Citybanan . In Melbourne and Brisbane several double track lines have

2208-409: A track circuited one. The low ballast resistance of very long track circuits reduces their sensitivity. Track circuits can automatically detect some types of track defect such as a broken rail. In the event of power restoration after a power failure, an axle counted section is left in an undetermined state until a train has passed through the affected section. A track circuited section immediately detects

2304-428: A train failure, or for a fast train to overtake a slow train. 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. The distance between

2400-588: A train to wait in a siding for a priority train to pass, and to maintain at least one block spacing between trains going the same direction. Timetable and train order operation was commonly used on American railroads until the 1960s, including some quite large operations such as the Wabash Railroad and the Nickel Plate Road . Train order traffic control was used in Canada until the late 1980s on

2496-466: A vast scale, with no requirements for any kind of communication that travels faster than a train. Timetable operation was the normal mode of operation in North America in the early days of the railroad. With the advent of the telegraph in 1841, a more sophisticated system became possible because this provided a means whereby messages could be transmitted ahead of the trains. The telegraph allows

2592-415: Is an example of a duplication line that was reduced to single-track in most locations, but has since undergone re-duplication in many places between Baltimore and Philadelphia when CSX increased freight schedules in the late 1990s. Also: Some lines are built as single-track with provision for duplication, but the duplication is never carried out. Examples are: When the capacity of a double-track railway

2688-411: Is an indication that another train is following the first and the waiting train must wait for the next train to pass. In addition, the train carrying the flags gives eight blasts on the whistle as it approaches. The waiting train must return eight blasts before the flag carrying train may proceed. The timetable system has several disadvantages. First, there is no positive confirmation that the track ahead

2784-931: 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 Ilfracombe Branch Line in the UK. Twinned structures may be identical in appearance, or like some tunnels between Adelaide and Belair in South Australia , substantially different in appearance, being built to different structure gauges . Tunnels are confined spaces and are difficult to duplicate while trains keep on running. Generally they are duplicated by building

2880-415: Is clear, only that it is scheduled to be clear. The system does not allow for engine failures and other such problems, but the timetable is set up so that there should be sufficient time between trains for the crew of a failed or delayed train to walk far enough to set warning flags, flares, and detonators or torpedoes (UK and US terminology, respectively) to alert any other train crew. A second problem

2976-414: Is common to use token systems that rely on the train driver's physical possession of a unique token as authority to occupy the line, normally in addition to fixed signals. Before allowing a train to enter a block, a signalman must be certain that it is not already occupied. When a train leaves a block, they must inform the signalman controlling entry to the block. Even if the signalman receives advice that

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3072-487: 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

3168-403: Is not allowed during times of poor visibility (e.g., fog or falling snow). Even with an absolute block system, multiple trains may enter a block with authorization. This may be necessary in order to split or join trains together, or to rescue failed trains. In giving authorization, the signalman also ensures that the driver knows precisely what to expect ahead. The driver must operate the train in

3264-515: Is quadruple tracked in most portions south of New Haven, but also has a few triple-track segments. The Metra Electric District is quadruple-tracked on most of the main line north of Kensington/115th Street station , with local trains running in the center two tracks, and express trains on the outer two tracks. Outside the United States the Chūō Main Line is an example of a modern, heavily utilized urban quadruple track railway. Quadruple track

3360-426: Is the origin of UK signalmen being referred to as "bob", "bobby" or "officer", when train-crew are speaking to them via a signal telephone) were employed to stand at intervals ("blocks") along the line with a stopwatch and use hand signals to inform train drivers that a train had passed more or less than a certain number of minutes previously. This was called "time interval working". If a train had passed very recently,

3456-419: Is the system's inflexibility. Trains cannot be added, delayed, or rescheduled without advance notice. A third problem is a corollary of the second: the system is inefficient. To provide flexibility, the timetable must give trains a broad allocation of time to allow for delays, so the line is not in the possession of each train for longer than is otherwise necessary. Nonetheless, this system permits operation on

3552-557: 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 Nevada , where the Western Pacific and Southern Pacific Railroads , longtime rivals who each built and operated tracks between northern California and Utah , agreed to share their lines between meeting points near Winnemucca and Wells , a distance of approximately 180 miles (290 km). Westbound trains from both companies used

3648-602: Is used in rapid transit systems as well: throughout the New York City Subway , the Chicago "L" 's North Side Main Line , and SEPTA 's Broad Street Line in the United States, and on the London Underground in the United Kingdom. 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

3744-424: Is very difficult to completely prevent conflicting orders being given, it is relatively simple to prevent conflicting tokens being handed out. Trains cannot collide with each other if they are not permitted to occupy the same section of track at the same time, so railway lines are divided into sections known as blocks . In normal circumstances, only one train is permitted in each block at a time. This principle forms

3840-509: The California Zephyr along these routes. Railway signalling Railway signalling ( BE ), or railroad signaling ( AE ), is a system used to control the movement of railway traffic. Trains move on fixed rails , making them uniquely susceptible to collision . This susceptibility is exacerbated by the enormous weight and inertia of a train, which makes it difficult to quickly stop when encountering an obstacle. In

3936-587: The Algoma Central Railway and some spurs of the Canadian Pacific Railway. Timetable and train order was not used widely outside North America, and has been phased out in favour of radio dispatch on many light-traffic lines and electronic signals on high-traffic lines. More details of North American operating methods is given below. A similar method, known as 'Telegraph and Crossing Order' was used on some busy single lines in

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4032-681: The Boyne Viaduct , a bridge just north of Drogheda railway station in Ireland ). The bridge over the Murray River between Albury and Wodonga is double-track, but because of insufficient strength in the bridge only one train is allowed on it at a time. The bridge has since been singled as part of the North East Line Standardisation with the old broad gauge track now disconnected but remains in place on

4128-558: The Canadian National main line in the Greater Toronto Area and Southern Ontario are triple track to facilitate high traffic density of freight services, intercity , and suburban passenger trains sharing the same lines. 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 miles)) for reducing

4224-584: The Hudson and New Haven Lines, both of which are shared between Metro-North and Amtrak in New York and Connecticut. The New Haven Line is quadruple track along its entire length, while the Hudson Line is only quadruple tracked along the shared portion from Riverdale to Croton–Harmon and along the shared track from Grand Central Terminal to Yankees–East 153rd Street . Amtrak 's Northeast Corridor

4320-619: 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. A double-track tunnel with restricted clearances is sometimes singled to form a single track tunnel with more generous clearances, such as the Connaught Tunnel in Canada or

4416-520: The UK , the Regulation of Railways Act 1889 introduced a series of requirements on matters such as the implementation of interlocked block signalling and other safety measures as a direct result of the Armagh rail disaster in that year. Most forms of train control involve movement authority being passed from those responsible for each section of a rail network (e.g. a signalman or stationmaster ) to

4512-450: The signalling systems, especially where the signalling is mechanical (e.g. semaphore signals ). Where the signals and points (UK term) or rail switches (US) are power-operated, it can be worthwhile to provide signals for each line which cater for movement in either direction, so that the double line becomes a pair of single lines. This allows trains to use one track where the other track is out of service due to track maintenance work, or

4608-425: The "train drivers". Foggy and poor-visibility conditions later gave rise to flags and lanterns. Wayside signalling dates back as far as 1832, and used elevated flags or balls that could be seen from afar. The simplest form of operation, at least in terms of equipment, is to run the system according to a timetable. Every train crew understands and adheres to a fixed schedule. Trains may only run on each track section at

4704-426: The 1880s, with full duplication completed around 1910. All bridges, tunnels, stations, and earthworks were built for double track. Stations with platforms with 11-foot (3.4 m) centres had to be widened later to 12-foot (3.7 m) centres, except for Gosford . The former Baltimore and Ohio Railroad (B&O) line between Baltimore and Jersey City , now owned by CSX and Conrail Shared Assets Operations ,

4800-546: The Daqin railway is operated by Daqin Railway Company Limited , a publicly traded stock company. Daqin railway carries over 1/5th of the coal transported by rail in China, more coal than any other railway line in China and the world. The line was constructed in two phases between December 1984 and December 1992, with specifications changed from single-track to double-track during construction. Design capacity

4896-734: The Southern Pacific's Overland Route , and eastbound trains used the Western Pacific's Feather River Route (now called the Central Corridor ). Crossovers were constructed where the lines ran in close proximity to allow reverse movements. This was necessary as while for most of this run the tracks straddle opposite sides of the Humboldt River , at points the two tracks are several miles apart and some destinations and branch lines can only be accessed from one of

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4992-551: The Tickhole Tunnel in New South Wales , Australia. In the case of the Tickhole Tunnel a new single-track tunnel was built and the two tracks in the original tunnel were replaced by one track in the centreline of the tunnel. Another case where this was necessary was the Hastings Line in the United Kingdom, where the tunnels were eventually singled to permit the passage of standard British-gauge rolling stock. Before

5088-511: The UK during the 19th century. However, a series of head-on collisions resulted from authority to proceed being wrongly given or misunderstood by the train crew - the worst of which was the collision between Norwich and Brundall, Norfolk, in 1874. As a result, the system was phased out in favour of token systems. This eliminated the danger of ambiguous or conflicting instructions being given because token systems rely on objects to give authority, rather than verbal or written instructions; whereas it

5184-523: The advantage of displaying the same aspects by night as by day, and require less maintenance than mechanical signals. Although signals vary widely between countries, and even between railways within a given country, a typical system of aspects would be: On some railways, colour light signals display the same set of aspects as shown by the lights on mechanical signals during darkness. Route signalling and speed signalling are two different ways of notifying trains about junctions. Under route signalling ,

5280-453: The appropriate position before the signal protecting that route can be cleared. UK trains and staff working in track circuit block areas carry track circuit operating clips (TCOC) so that, in the event of something fouling an adjacent running-line, the track circuit can be short-circuited. This places the signal protecting that line to 'danger' to stop an approaching train before the signaller can be alerted. An alternate method of determining

5376-443: The basis of most railway safety systems. Blocks can either be fixed (block limits are fixed along the line) or moving blocks (ends of blocks defined relative to moving trains). On double tracked railway lines, which enabled trains to travel in one direction on each track, it was necessary to space trains far enough apart to ensure that they could not collide. In the very early days of railways, men (originally called 'policemen', which

5472-436: The block is clear. Most blocks are "fixed", i.e. they include the section of track between two fixed points. On timetable, train order, and token -based systems, blocks usually start and end at selected stations. On signalling-based systems, blocks start and end at signals. The lengths of blocks are designed to allow trains to operate as frequently as necessary. A lightly used line might have blocks many kilometres long, but

5568-588: The bridge. 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. Severe gradients can make the headway in the uphill direction much worse than the headway in the downhill direction. Between Whittingham and Maitland, New South Wales ,

5664-528: 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 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 commuter rail or rapid transit . The layout can vary, often with

5760-535: The choice of which side the driver should sit is 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. Generally,

5856-400: 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: Handedness of traffic can affect locomotive design. For the driver, visibility is usually good from both sides of the driving cab, so

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5952-498: 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. 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

6048-413: The dissemination of any timetable changes, known as train orders . These allow the cancellation, rescheduling and addition of train services. North American practice meant that train crews generally received their orders at the next station at which they stopped, or were sometimes handed up to a locomotive 'on the run' via a long staff. Train orders allowed dispatchers to set up meets at sidings, force

6144-440: The driver, or rotated so as to be practically invisible. While this type of signal is still in use in some countries (e.g., France and Germany), by far the most common form of mechanical signal worldwide is the semaphore signal . This comprises a pivoted arm or blade that can be inclined at different angles. A horizontal arm is the most restrictive indication (for 'danger', 'caution', 'stop and proceed' or 'stop and stay' depending on

6240-525: 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 telegraph and the train order system. 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

6336-545: The end of the block for at least the distance required to stop the train. In signalling-based systems with closely spaced signals, this overlap could be as far as the signal following the one at the end of the section, effectively enforcing a space between trains of two blocks. When calculating the size of the blocks, and therefore the spacing between the signals, the following have to be taken into account: Historically, some lines operated so that certain large or high speed trains were signalled under different rules and only given

6432-404: The entire train has left the section. If part of the train remains in the section, the track circuit detects that part. This type of circuit detects the absence of trains, both for setting the signal indication and for providing various interlocking functions—for example, preventing points from being moved while a train is approaching them. Electrical circuits also prove that points are locked in

6528-444: The following train was expected to slow down to allow more space to develop. The watchmen had no way of knowing whether a train had cleared the line ahead, so if a preceding train stopped for any reason, the crew of a following train would have no way of knowing unless it was clearly visible. As a result, accidents were common in the early days of railways. With the invention of the electrical telegraph , it became possible for staff at

6624-517: 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. Double-track railways, especially older ones, may use each track exclusively in one direction. This arrangement simplifies

6720-490: The length and width of trains is contingent on the minimum railway curve radius of the railway. 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. 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

6816-423: The lines. There is a grade separated crossover of the two lines in the shared track area near Palisade, Nevada , which results in trains following right hand traffic in the eastern half of the shared track area, but left hand traffic in the western half. The Union Pacific Railroad has since acquired both of these lines, and continues to operate them as separate lines using directional running. Amtrak also runs

6912-539: The local train stations, the express trains can pass through the station at full speed. For example on the Nuremberg-Bamberg railway , which is quadruple track for most of its course, the inner two tracks are used by the S-Bahn Nuremberg whereas the outer tracks are used for regional express and Intercity Express trains. The section in northern Fürth where the line is "only" double track creates

7008-560: 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 Main Southern railway line in Australia between Junee and Albury . This

7104-403: The next section, and an electric current is fed to both running rails at one end. A relay at the other end is connected to both rails. When the section is unoccupied, the relay coil completes an electrical circuit, and is energized. However, when a train enters the section, it short-circuits the current in the rails, and the relay is de-energized. This method does not explicitly need to check that

7200-434: The occupied status of a block uses devices located at its beginning and end that count the number of axles that enter and leave the block section. If the number of axles leaving the block section equals those that entered it, the block is assumed to be clear. Axle counters provide similar functions to track circuits, but also exhibit a few other characteristics. In a damp environment an axle counted section can be far longer than

7296-667: The older DJ1 models. 24 August 2020 - Four cars of a train derailed near Zhuolu railway station in Zhuolu County , Hebei province. No casualties were reported. 14 April 2022 - 17 cars of a freight train derailed after colliding with a parked locomotive near Cuipingshan railway station in Jizhou District, Tianjin , 11 of which fell off from the elevated railway. No casualties or injuries have been reported. Double track A double-track railway usually involves running one track in each direction, compared to

7392-666: 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: 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

7488-442: The outer tracks use bi-directional running and serve local trains exclusively in one direction. During service disruptions on one of the two outer tracks, trains could also bypass the affected sections on the center track. The Union Pacific Railroad mainline through Nebraska has a 108-mile (174 km) stretch of triple track between North Platte and Gibbon Junction, due to a high traffic density of 150 trains per day. Portions of

7584-727: The partial reinstatement of double track. In New Zealand the Melling Line was singled to the Western Hutt Railway Station in Lower Hutt in 1958 after it became a branch line rather than part of the main Hutt Valley Line . Kirkby railway station (until 1977) and Ormskirk railway station (until 1970) were double-track railway, when they were converted into single-track railway with cross-platform interchange . In New South Wales, Australia,

7680-416: The presence of a train in section. On most railways, physical signals are erected at the lineside to indicate to drivers whether the line ahead is occupied and to ensure that sufficient space exists between trains to allow them to stop. Older forms of signal displayed their different aspects by their physical position. The earliest types comprised a board that was either turned face-on and fully visible to

7776-410: The previous train has left a block, they are usually required to seek permission from the next signal box to admit the next train. When a train arrives at the end of a block section, before the signalman sends the message that the train has arrived, they must be able to see the end-of-train marker on the back of the last vehicle. This ensures that no part of the train has become detached and remains within

7872-408: The replacement of manual block systems such as absolute block with automatic block signalling. Under automatic block signalling, signals indicate whether or not a train may enter a block based on automatic train detection indicating whether a block is clear. The signals may also be controlled by a signalman, so that they only provide a proceed indication if the signalman sets the signal accordingly and

7968-479: The required speed over a junction onto which they have been diverted due to some emergency condition. Several accidents have been caused by this alone. For this reason, in the UK, where all lines are route signalled, drivers are only allowed to drive on routes that they have been trained on and must regularly travel over the lesser used diversionary routes to keep their route knowledge up to date. Many route signalling systems use approach control (see below) to inform

8064-636: The right of way if two blocks in front of the train were clear. Under a moving block system, computers calculate a safe zone around each moving train that no other train is allowed to enter. The system depends on knowledge of the precise location and speed and direction of each train, which is determined by a combination of several sensors such as radio frequency identification along the track, ultra-wideband, radar, inertial measurement units, accelerometers and trainborne speedometers ( GNSS systems cannot be relied upon because they do not work in tunnels). Moving block setups require instructions to be directly passed to

8160-424: The section. The end of train marker might be a coloured disc (usually red) by day or a coloured oil or electric lamp (again, usually red). If a train enters the next block before the signalman sees that the disc or lamp is missing, they ask the next signal box to stop the train and investigate. Under a permissive block system, trains are permitted to pass signals indicating the line ahead is occupied, but only at such

8256-556: The singling, narrow-bodied stock, specially constructed for the line, had to be used. As part of the Regional Fast Rail project in Victoria, Australia , the rail line between Kyneton and Bendigo 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

8352-626: 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 signal bridges . For standard gauge tracks the distance may be 4 metres (13 ft) or less. Track centres are usually further apart on high speed lines, as pressure waves knock each other as high-speed trains pass. Track centres are also usually further apart on sharp curves, and

8448-400: The traffic load and delays in passenger train arrivals. The construction between Bina and Bhopal and between Itarsi and Budhni had been completed by April 2020. 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

8544-467: The train crew. The set of rules and the physical equipment used to accomplish this determine what is known as the method of working (UK), method of operation (US) or safe-working (Aus.). Not all these methods require the use of physical signals , and some systems are specific to single-track railways. The earliest rail cars were hauled by horses or mules. A mounted flagman on a horse preceded some early trains. Hand and arm signals were used to direct

8640-441: The train instead of using lineside signals. This has the advantage of increasing track capacity by allowing trains to run closer together while maintaining the required safety margins. Centralized traffic control (CTC) is a form of railway signalling that originated in North America. CTC consolidates train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of

8736-419: The two outer tracks carrying the local trains that stop at every station so one side of stations can be reached without staircase; this can also be reversed, with express trains on the outside and locals on the inside, for example if staffed ticket booths are wanted, allowing one person for both directions. At other places two tracks on one half of the railway carry local trains and the other half faster trains. At

8832-489: 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

8928-404: 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. 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

9024-409: The type of signal). To enable trains to run at night, one or more lights are usually provided at each signal. Typically this comprises a permanently lit oil lamp with movable coloured spectacles in front that alter the colour of the light. The driver therefore had to learn one set of indications for daytime viewing and another for nighttime viewing. Whilst it is normal to associate the presentation of

9120-442: Was 100 million tonnes a year, which it reached after ten years, but continuous upgrades (wider subgrade, 75 kg/m rails, wagons with higher capacity and top speed, longer trains and stronger locomotives, radio operation and centralised traffic control, automatic train inspection) quadrupled capacity. In 2006, powerful locomotive models HXD1 and HXD2 , with 9.6 MW and 10 MW power output respectively, entered Daqin line to replace

9216-410: 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. The process of expanding a single track to double track

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