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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.
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Merits of quadruple track
- Quadruple track can manage larger amount of traffic with usually one and a half or twice larger capacity of double track. It is often seen around large metropolis or busy inter-city corridor with large demand consequently.
- 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 with 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).
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, and short distance commuter rail are separated. 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.
- 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
- 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.
- 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 Pennsylvania Railroad had a four-track mainline carrying freight from Pittsburgh to Harrisburg via the Horseshoe Curve.
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