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 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. 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. Advantages and tradeoffs Island platforms are necessary for any station with many through platforms. There are also advantages to building small two-track stations with a single island platform instead of two side platforms. Island platforms allow facilities such as shops, toilets and waiting rooms to be shared between both tracks rather than being duplicated or present only on one side. An island platform makes it easier for disabled travellers to change services between tracks or access facilities. If the tracks are above or below the entrance level, the station needs only one staircase and (if disabled accessibility is necessary) one elevator or ramp to allow access to the platforms. If the tracks are at the same level as the entrance, this instead creates a disadvantage; a side platform arrangement allows one platform to be adjacent to the entrance, whereas an island platform arrangement requires both tracks to be accessed by a bridge or underpass. If an island platform is not wide enough to cope with passenger numbers, overcrowding can be a problem. Examples of stations where a narrow island platform has caused safety issues include Clapham Common and Angel (rebuilt in 1992) on the London Underground, Union (now rebuilt) on the Toronto subway, and on the Osaka Municipal Subway. An island platform requires the tracks to diverge around the center platform, and extra width is required along the right-of-way on each approach to the station, especially on high-speed lines. Track centers vary for rail systems throughout the world but are normally 3 to 5 metres.