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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 consisting of six parallel tracks, or a sextuple-track railway, consist of 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.
- 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.
- Quadruple track costs more due to requiring more materials and increased land acquisition costs. This also applies to tunnelling 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 (points) on the track than on a two-track line (to facilitate switching from outer to inner tracks and vice versa).
- For safety, costly grade separations are almost always required.
- If needing more capacity, it can be better to add a double track along a different route, because it could improve local and regional transit much along an under-served route, and reduce land acquisition cost by choosing a less built-up area.
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:
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.
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.
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.
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.
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). 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.
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.
- 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 112 km long Hamm–Minden railway between Hamm and Minden in Germany is completely quadruple-track with separate tracks for freight and passenger trains.
- The 50 km long railway from Rastatt to Offenburg in Germany has four tracks.
- The Hohenzollern Bridge, with six tracks
- The line from Munich to Augsburg has four tracks and near Munich even more.
- 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.
- The 120 km 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).
- Significant lengths of the West Coast Main Line, Great Western Main Line, South Wales Main Line, Midland Main Line, South West Main Line, Brighton Main Line, Chatham Main Line, South London line, Windsor Lines between Barnes railway station and Clapham Junction railway station and East Coast Main Line in Great Britain are quadruple track, with the remainder of the lines being double track. These lines are high capacity, intercity rail routes.
- 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.
- The Metro-North Railroad's New Haven Line is four-tracked from Grand Central Terminal in New York City to New Haven Union Station in New Haven, Connecticut, while the system's Hudson Line features quadruplicated tracks for most of its length between Croton-Harmon and Spuyten Duyvil.
- Much of Amtrak's Northeast Corridor from Washington, D.C., to New Haven, Connecticut, is a four-track line, except for the segment between New Rochelle and the Sunnyside Yard in Queens, New York. In the Bronx, the Amtrak trains run separately from the New Haven Line. The right-of-way from Woodside, Queens, over the Hell Gate Bridge to Co-op City, Bronx, is three-tracked due to the presence of the single-tracked New York Connecting Railroad.
- The Erie Lackawanna Railway had a four-track mainline on the former Erie Railroad, from its Pavonia Terminal in Jersey city to Suffern yard in Rockland County, New York. This allowed the separation of freight and commuter trains. The EL Rwy also inherited former Lackawanna four-track Boonton Main Line from Dover, NJ, to Delawanna (Passaic), NJ.
- The Central Railroad of New Jersey had a four-track main from the CNJ Terminal in Jersey City to Phillipsburg, NJ, across from Easton, PA.
- The Long Island Rail Road's Main Line is four-tracked from its East River Tunnels portal in Long Island City to Queens Village, NY.
- 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.
- 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. Hence, many express services are operated in the New York City Subway. Express trains and local trains are separated from each different track.
- SEPTA's Center City Commuter Connection in Philadelphia is quadruple track, as is about half of Philadelphia's Broad Street Subway.
- 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.
- 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 10 km 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.
- Between Tokyo and Odawara (JR East) 83.9 km is paired by use (not including Shinkansen).
- Tokyo – Shinagawa 6.8 km: 6 tracks (8 if include Sobu-Yokosuka Line Underground)
- Shinagawa – Tsurumi 14.9 km: 4 tracks
- Tsurumi – Yokohama 7.1 km: 6 tracks
- Yokohama – Totsuka 12.1 km: 4 tracks
- Totsuka – Ofuna 5.6 km: 6 tracks
- Ofuna – Odawara 37.4 km: 4 tracks
- Between Tokyo and Omiya (JR East) is paired by use (not including Shinkansen)
- Tokyo – Akihabara: 6 tracks
- Akihabara – Ueno: 6 tracks
- Ueno – Nippori 2.2 km: 10 tracks (2 for Ueno Depot)
- Nippori – Tabata: 4 tracks
- Nippori – Oku: 4 tracks
- Tabata – Akabane: 4 tracks
- Oku – Akabane: 2 tracks
- (Nippori – Akabane 7.4 km)
- Akabane – Omiya 17.1 km: 6 tracks
- Between Kusatsu and Nishi-Akashi (JR West) 120.9 km (not including Shinkansen)
- Kusatsu – Kyoto 22.2 km is paired by direction: 4 tracks
- Kyoto – Umekoji – Mukomachi 6.4 km is paired by direction: 5 tracks
- Mukomachi – Ibaraki 21.8 km is paired by direction: 4 tracks
- Ibaraki – Suita is paired by use: 6 tracks
- Suita – Shin-Osaka is paired by use: 8 tracks
- Shin-Osaka – Osaka – Tsukamoto is paired by direction: 6 tracks
- (Ibaraki – Osaka 14.6 km)
- Shin-Osaka – Miyahara – Tsukamoto: 2 tracks
- Tsukamoto – Hyogo is paired by direction: 4 tracks
- Hyogo – Takatori is paired by direction: 5 tracks
- (Osaka – Takatori 38.2 km)
- Takatori – Nishi-Akashi 17.7 km is paired by use: 4 tracks
- Between Ochanomizu and Mitaka (JR East) 21.5 km is paired by use.
- Ochanomizu – Yoyogi: 4 tracks
- Yoyogi – Shinjuku: 8 tracks
- Shinjuku – Mitaka: 4 tracks
- Between Kinshicho and Chiba (JR East) 34.4 km is paired by use.
- Kinshicho – Nishi-Chiba: 4 tracks
- Nishi-Chiba – Chiba: 6 tracks
- Between Ayase and Toride (JR East) 29.7 km: 4 tracks/paired by use
- Between Osaki and Komagome (JR East) about 20 km is paired by use. (see Yamanote line)
- Osaki – Yoyogi: 4 tracks
- Yoyogi – Shinjuku: 8 tracks
- Shinjuku – Komagome: 4 tracks
- Between Souen and Heiwa (JR Hokkaido) about 9 km
- Souen – Sapporo is paired by use: 3 tracks
- Sapporo – Heiwa is paired by direction: 4 tracks
- Between Niigata and Kami-Nuttari (JR East) 1.9 km: 4 tracks/paired by direction
- Between Imamiya and Tennoji (JR West) 2.2 km: 4 tracks/paired by direction
- Between Inazawa and Nagoya (JR Central) 11.1 km/paired by use: 4 tracks
- Between Hiroshima and Kaitaichi (JR West) 6.4 km: 4 tracks/paired by direction
- Between Orio and Moji (JR Kyushu) 24.6 km
- Orio – Kokura: 4 tracks/paired by use
- Kokura – Higashi-Kokura 1.6 km/paired by direction: 6 tracks
- Higashi-Kokura – Moji is paired by direction: 4 tracks
- Besides JR companies, the following private railway companies in Japan run their own quadruple (or more) tracked sections:
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.
- The NSCR will run alongside the Metro Manila Subway between FTI and Bicutan stations from ARCA Road to Mañalac Avenue. Length is 2,628 m (8,622 ft).
- A branch line to Clark International Airport will have a flyover interchange with the mainline, creating a 1,520 m (4,990 ft) quadruplicated section.
- A spur to the Mabalacat depot will diverge from the main branch, the latter heading underground. Length is 1,000 m (3,300 ft).