Quadruple-track railway
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Quadruple track railway consists of four parallel tracks. On a quad-track line, two tracks are used in each direction. It is also sometimes called four-track railway.
Some tracks are only triplicated, having only one extra track to relieve congestions, while some tracks are sextuplicated, i.e., three pairs of tracks with three tracks on each direction.
Advantages of quadruple track
- Quadruple track can manage a larger amount of traffic with usually twice the capacity of double track. It is often seen around large metropolis or on busy inter-city corridors.
- In quadruple track, faster trains can overtake slower ones, and quadrupling can contribute to faster operation of trains. High-speed rail of 200 km/h average speed and commuter rail of 40 km/h average can co-exist in quadruple track without interrupting each other.
- It is relatively easy to do maintenance and engineering work of tracks in quadruple line with minimum effect of train delay because double-track service is kept even if the other two double tracks are halted during the work.
Disadvantages of quadruple track
- Quadruple track costs more due to requiring more materials and increased land acquisition costs. This also applies to tunneling and bridge costs.
- When adding tracks, land acquisition can become prohibitively expensive.
- Maintenance costs are higher and often more complex as there may be more switches on the track than on a two-track line (to facilitate switching from outer to inner tracks and vice versa).
- For safety reasons, grade separations are almost always required.
Quadruple track operation
In quadruple track, trains are sorted in various ways in order to make maximum use of track capacity. These can include one or a combination of:
- Sorting by speed
A faster express line and a stopping local line are separated, with each having a separate pair of tracks.
Construction of new double tracks dedicated to high-speed rail alongside existing conventional double track used by regional and local passenger trains and freight trains is a form of quadruple track. It increases the capacity of that route significantly, and allows for significant increases in inter-city high-speed train frequency with reduced travel times.
- Sorting by distance
Long distance inter-city rail and freight trains are separated from short distance commuter rail. This helps to prevent delays on one service affecting the other, and is commonly seen in metropolitan areas. Quadruplication may be necessary when a new commuter rail service begins to operate on an existing line. Sometimes the local trains have separate technology, such as electrical system or signalling, which requires strict separation, for example in Berlin or Copenhagen.
- Sorting by destination
When a quadruple track line divides to different destinations part way along, trains need to be sorted by their destination.
- Sorting by passenger/ freight
Passenger trains and freight trains can be separated with each different track.
A variation of this can be found on the quadruple track section of the Main North railway line in New South Wales between Waratah and Maitland where one pair of tracks are used exclusively for coal trains and the other pair are used for passenger trains and general freight. A similar process, but with all intercity and commuter passenger trains on the outer tracks and thru-freight trains on the inner tracks, was done by the Pennsylvania Railroad on its New York-Washington and Philadelphia-Pittsburgh mainlines prior to the takeover of operations by Amtrak and Conrail (and later Norfolk Southern). This is somewhat still done to this day by NS, CSX, and Conrail Shared Assets trains on Amtrak-owned trackage in the Philadelphia area.
- Other modes
Two double track lines along opposite sides of a river can operate as a quadruple track. Examples of this can be found in Rhone in France and Rhine in Germany.
Examples
America
- The New York Central Railroad's Water Level Route was the first long distance 4-track railroad in the world.[citation needed]
- Much of Amtrak's Northeast Corridor from Washington to New Haven is a four track line.
- The Pennsylvania Railroad had a four-track mainline carrying freight from Pittsburgh to Harrisburg via the Horseshoe Curve. This was how the name Broadway Limited came about due the "Broadway of a 4 track main."
- New York City Subway - many lines of the New York City Subway are quadrupled. Hence, many express services are operated in the New York City Subway. Express trains and local trains are separated with each different track.
Europe
- Significant lengths of the West Coast, Great Western and East Coast Main Lines in Great Britain are quadruple track, with the remainder of the lines being double track. These lines are high capacity and high speed lines running from Glasgow, Bristol and Edinburgh to London.
- The London Waterloo to Southampton / Salisbury main line South Western Main Line from London Waterloo to Worting Junction, Great Britain.
- The Berlin Stadtbahn, Germany, has four tracks.
Asia
- The Tung Chung Line and the Airport Express in Hong Kong are quadruplicated between Kowloon and Tsing Yi stations, but share two tracks on the rest of their routes (until they diverge before the western end). The two lines shared two tracks when they were opened in 1998.
- The Gyeongbu Line in South Korea is quadruplicated on 84.9km on its route, and sextuplicated on a further 11.7km
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