A quadruple-track railway (also known as a four-track railway) is a railway line consisting of four parallel tracks with two tracks used in each direction. Quadruple-track railways can handle large amounts of traffic, and so are used on very busy routes or sections. Such conversion is referred to as "quadruplication".
A railway line with six parallel tracks, or a sextuple-track railway, has three tracks in each direction. The corresponding term is "sextuplication".
There are also instances of railway lines or sections with eight tracks, and cases with three or five tracks. All experience similar upsides and downsides.
Advantages
Quadruple track can carry a larger amount of traffic, and through scheduling techniques like express trains can actually allow for more than twice the capacity of a double-track corridor. It is often seen around large metropolises or on busy inter-city corridors, with the most extensive urban usage seen on the New York City Subway.
On quadruple track, faster trains can overtake slower ones, and so quadrupling allows all trains to reach their maximum speed. For example, high-speed rail with a 200km/h average speed and commuter rail with a 60km/h average can co-exist on quadruple tracks without interrupting each other.
Maintenance and engineering work are easier on tracks in quadruple line with little resulting delay because standard double-track service can continue even if the other two double tracks are halted during the work.
Quadruple track lines generally benefit from economies of scale in many other facets due to their larger capacities, from construction, operation, maintenance, storage, and services. Quad-track rail offers a cost-efficient model for high capacity rail service corridors.
Disadvantages
Quadruple tracking costs more per mile, as it requires more materials and increased land acquisition costs. The required right-of-way is naturally wider, while interchanges and signaling become more complex, and track switching more frequent. This also applies to tunnelling and bridge costs.
Maintenance costs are higher and often more complex, as there may be more switches on the track than on a two-track line, to allow moving between each of the 4 tracks.
In order to maintain high speeds, grade separations are commonly required.
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. Quadrupling 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 Northern 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. Future passenger and freight-separated track pairs are planned by the state of Virginia on the corridor between Washington, D.C. and Richmond, Virginia, and by California High-Speed Rail between Los Angeles and Fullerton, California.
Other modes
Two separate double-track lines in proximity to each other, e.g., two double-track lines along opposite sides of a river, can operate as a quadruple track line. Examples of this can be found in Rhone in France and Rhine in Germany.
Layouts
As it can be seen from the pictures below in the Gallery of diagrams, the four tracks can be paired either by direction (slow and fast in each pair) or by purpose (speed or direction in each pair). Pairing by direction allows the railway to interface to a double track more easily. With fast trains in centre, local stations can be on the outside, eliminating staircases for half the passengers. With slow trains in centre or when pairing by speed there can be a common platform for local trains with one staircase and one ticket booth.
Sometimes two of the tracks go more straight and with a little distance from the two other. This is a design decision when widening a double track section, and allows higher speed on the faster tracks.
Examples
Belgium
Several lines radiating from Brussels are quadrupled, for instance the Ghent-Ostend line as far as Essene-Lombeek. Further quadrupling has recently been carried out as part of the development of the Brussels Regional Express Network. The building of high-speed lines has also led to quadrupling - for instance the HSL 2 high-speed line between Brussels and Cologne runs inside the local lines as far as Leuven. Meanwhile since 1934 Brussels and Antwerp have been connected by two separate pairs of double track. Fast trains normally use line 25, while line 27 serves slow trains. In places they run parallel, but at times diverge and cross over each other.
Denmark
There are two places in Denmark with four tracks:
Between Klampenborg and Høje Taastrup, through Copenhagen, Denmark, there are four tracks; two are for the separated S-trains and two for mainline trains; where the two tracks closest to Copenhagen (the oldest and central parts of Copenhagen) are reserved for S-trains (on much the lines this is the Northern and Western two tracks).
Also between Høje Taastrup and Roskilde, where the two center tracks are for InterCity, long distance commuter trains (further than Roskilde or Ringsted), while the outer two tracks are for commuter trains to/from Ringsted or Holbæk. It has been suggested that the S-trains should continue from Høje Taastrup to Roskilde, but this plan was abandoned; partly due to Roskilde refusing the offer for fear they would become a suburb of Copenhagen, and partly due to construction costs which would exceed the advantages.
By definition German railway lines have one or two tracks. Where more tracks are running parallel to each other, they are considered two or more separate lines. Such routes include:
The Berlin Stadtbahn, Germany, has four tracks. Two are for the separated S-Bahn and two for mainline trains.
The 112km long Hamm–Minden railway between Hamm and Minden in Germany is completely quadruple-track with separate tracks for freight and passenger trains.
The 50km long railway from Rastatt to Offenburg in Germany has four tracks.
The Rome–Naples high-speed railway and the Rome–Sulmona–Pescara railway in Italy combine to form a quadruple track section between Roma Prenestina railway station and Salone railway station.
The Milan-Chasso railway and the Milan-Lecco railway run parallel in a quadruple track section from Milan to Monza.
The main section of Ferrovie Nord Milano line between Milan and Saronno in Italy. Outer regional trains are segregated from the inner suburban trains.
Netherlands
The Amsterdam–Rotterdam railway between Leiden via Den Haag HS to Rijswijk was quadrupled between 1987 and 1996. As of 2023[update], work is underway to extend this to Delft, although the last few kilometers to Schiedam, near Rotterdam are to remain double track.
There are some quadruple-track railways in the Oslo region. They are mostly two double tracks with slightly different routes, one older for local trains, and one newer mostly in tunnels for high-speed and regional trains.
The suburban railway axis between Agualva-Cacém and Alverca in the Lisbon Metropolitan Area, excluding a small section between Roma-Areeiro and Braço de Prata, which will be quadruplicated by 2030. This is part of the Linha de Sintra, Linha da Cintura and Linha do Norte, which are Portugal's busiest railway lines by number of passengers and trains. The former two are suburban lines in Lisbon; while the latter is the long-distance route to Porto, with Intercity and High-Speed services. A set of tracks is for the suburban services and the other two are for long-distance trains.
Serbia
Section between Batajnica and Stara Pazova, around 15 km long, on Belgrade–Šid and Belgrade–Subotica railways is quadruplicated from 2022. Two inner tracks are used by passenger trains and have maximum speed 200 km/h while two outer tracks are used for freight trains.
Sweden
All of the mainline railway through Stockholm County (between Järna and Myrbacken north of Märsta, 83km or 52mi) has four tracks, sometimes having two routes. There are plans to widen Stockholm–Bålsta and Myrbacken–Uppsala to quadruple track with parts finished or under construction. After this, the Stockholm commuter rail would have its own tracks everywhere. The Swedish Transport Administration is currently planning on extending the quadruple track from a few kilometers north off Upplands Väsby to Uppsala Central Station within the upcoming decade. When having four tracks the local trans go in the middle, which allows a common ticket booth per station.
The section between Malmö and Arlöv on the Southern Main Line has four tracks, and an extension to Lund was finished in 2024. It will have local stations on the outside tracks, because staffed ticket booths are not used here.
Switzerland
The 120km long railway from Zürich to Olten contains long quadruple track sections from Zürich to Killwangen-Spreitenbach (Zürich–Baden line) and from Rupperswil to Aarau (Heitersberg line), currently being extended to Olten (Olten–Aarau line).
A quadruple set of tracks exists in the Roca Line railway in Greater Buenos Aires between Constitución station and Temperley. All four tracks are used by commuter trains, 2 tracks are used for direct service and the other 2 for regular service.
Many lines of the New York City Subway are quadrupled – one of the few rapid transit systems in the United States to have extensive duplication. Express and local trains are separated on different sets of tracks.
Much of Amtrak's Northeast Corridor from Newark, Delaware, to New Haven, Connecticut, is a four-track line.
One exception is the segment between New Rochelle and the Sunnyside Yard in Queens, where the Northeast Corridor occupies two tracks, although in its southern portion it is alongside one or two freight tracks. The right-of-way from Woodside, Queens, over the Hell Gate Bridge to the Oak Point Link junction is in total three-tracked, although it was historically four-tracked before one of the freight tracks was lifted. The bridge was also designed for an additional track on each side of the main arch for a trolley line.
The New York Central's Water Level Route across upstate New York was four-tracked in the majority as early as 1876, claiming to be the earliest 4-tracked steel main. This was extended to Buffalo by 1936. Financial troubles and changing traffic patterns caused this to be downgraded to a double track by 1975. However a southern portion used by the Metro-North RailroadHudson Line features quadruplicated tracks for most of its length between Croton-Harmon and Spuyten Duyvil.
The Pennsylvania Railroad had a four-track mainline carrying freight from Pittsburgh to Harrisburg via the Horseshoe Curve (Pennsylvania). This was how the name Broadway Limited came about from the "Broadway of a 4-track main." Much of the route between Pittsburgh and Paoli has been downgraded to three or two tracks.[citation needed]
Reading Company's New York Branch between Neshaminy Falls and Yardley station was originally quadruple-tracked before being reduced to three tracks between Neshaminy Falls and Woodbourne station and two tracks between Woodbourne and Yardley. In 2016, the third track between Woodbourne and Yardley was relaid by SEPTA in order to separate SEPTA's West Trenton Line and CSX's Trenton Subdivision.
Market Street in San Francisco had quadruple track streetcars for much of its length in the early 1900s – two tracks operated by United Railroads of San Francisco and two tracks operated by the San Francisco Municipal Railway (Muni). As the streetcar system was acquired by the government and was modernized to light rail, capacity was maintained by tunneling an additional right-of-way for Muni vehicles parallel, under the surface. The Market Street subway's two subterranean levels are both double-tracked, and the (retained) double-tracked surface section runs heritage trolley cars for a total of six tracks in the same thoroughfare. The surface and upper level are laid at standard gauge and maintained by the San Francisco Municipal Transportation Agency while the lower level is Indian gauge track operated by Bay Area Rapid Transit.
Bay Area Rapid Transit is quadruple tracked for a short section at the approaches to and at MacArthur station in Oakland, California. The transit system had plans that called for Market Street subway to be fully quadruple tracked to their unique operational specifications, with express trains running on a separate level than local trains; the final system was reconfigured due to budget constraints.
The Guangzhou–Shenzhen Railway is quadruplicated in 2007 for its entire length separating high-speed passenger with freight and conventional passenger services. It is the first railway in China to do so. The third track was added in 2000, but the mixing of services heading in one direction caused disruption in schedules, so the fourth track was built allowing for complete separation.
The Harbin–Qiqihar intercity railway runs beside the older Harbin–Manzhouli railway between Harbin and Houwujiacun.
The Hangzhou–Huangshan intercity railway runs beside the Hefei–Fuzhou high-speed railway between Huangshan North and Jixi North with a pair of tracks for each line.
Six tracks run between Hangzhou East and Hangzhou South railway stations.
The Zhengzhou–Jiaozuo intercity railway runs beside the older Beijing–Guangzhou railway between the New Yellow River Jingguang Railway Bridge to Nanyangzhai railway station with a pair of tracks for each line.
The Tung Chung line and the Airport Express of the MTR in Hong Kong are quadruplicated between Kowloon and Tsing Yi stations, but share two tracks through the Western Immersed Tube tunnel and between Tsing Yi and Sunny Bay stations and between Sunny Bay station and Tai Ho Wan junction.
The Tuen Ma line runs parallel to the Tung Chung line and the Airport Express near Nam Cheong station, meaning six tracks running side-by-side, though the three lines serve different destinations and passenger interchange is only possible between Tung Chung line and the Tuen Ma line at Nam Cheong, and out-of-system across the three lines between Austin and Kowloon stations.
The line between Manggarai and Cikarang on Rajawali-Cikampek line is being quadrupled, with the first section between Jatinegara and Cakung opened on 14 April 2019.
Israel
The Coastal Railway between Tel Aviv Central and Herzliya. In 2020 construction started on an NIS 5.5 billion (US$1.5 billion in 2018 dollars) project to extend the 4 track section along about 10km south from Tel Aviv Central to Tel Aviv HaHagana and from there to the Ganot/Shapirim interchange on the Tel Aviv–Lod Railway. In the future, four tracking of the Coastal Railway is also planned to extend north of Herzliya to Haifa in stages.
The country never implemented a quadruple-track line throughout its history, but there are plans for sections of the North–South Commuter Railway (NSCR) to be quadruplicated.
↑"Sec. A2". Basic Design. The Detailed Design Study (including Supplementary Feasibility Study) of the South Commuter Railway Project Package CP S-03b (Report). Vol.II. Japan International Cooperation Agency, Tokyo Metro, et al. 2021-03-24.
12"Sec. 6". MCRP Detailed Design. The Detailed Design Study (including Supplementary Feasibility Study) of the Malolos Clark Railway Project Package CP N-04 (Report). Vol.II. Japan International Cooperation Agency, Tokyo Metro, et al. 2019-05-06.
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