Center platform

An island platform (also center platform, centre platform) is a station layout arrangement where a single platform is positioned between two tracks within a railway station, tram stop or transitway interchange. Island platforms are popular on twin-track routes due to pragmatic and cost-effective reasons. They are also useful within larger stations where local and express services for the same direction of travel can be provided from opposite sides of the same platform thereby simplifying transfers between the two tracks. An alternative arrangement is to position side platforms on either side of the tracks.

Station with two tracks
and one island platform

The historical use of island platforms depends greatly upon the location. In the United Kingdom the use of island platforms is relatively common when the railway line is in a cutting or raised on an embankment, as this makes it easier to provide access to the platform without walking across the tracks.

The island platform layout is a popular, cost-effective and practical solution in the modern railway systems. Island platforms allow facilities such as escalators, elevators, shops, toilets and waiting rooms to be shared between both tracks rather than being duplicated or present only on one side. This is essential for wheelchair accessible stations. An island platform makes it easier for wheelchair users and the infirm to change services between tracks. Additionally, an island platform layout eliminates the need to construct a crossover or crossunder between two platforms. However, island platforms may become overcrowded, especially at busy stations, and this can lead to safety issues such as Clapham Common (see image) and Angel (now rebuilt) on the London Underground (as well as Union (now rebuilt) on the Toronto subway and Umeda on the Osaka Municipal Subway).

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Wikipedia