Quadruple-track railway


A quadruple-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.

Advantages

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.
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. 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 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.

Layouts

As it can be seen from the pictures below in the Gallery of diagrams, the four tracks can be paired either by direction or by purpose. 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

Europe

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

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:

United States

East coast

China

Australia