Express trains (also sometimes referred to as fast trains, though this is a relative term, usually meaning "faster than some other trains on the line in question") are a form of rail service. Express trains make only a small number of stops, instead of stopping locally. In some cases, trains run express where there is overlapping local train service available, and run local at the tail ends of the line, where there is no supplemental local service. During overnight hours, or other times where it is practical, express trains may become local, but still running to where an express train would terminate. While widely implemented in long-distance rail service, it has also proven successful in the planning of some rapid transit systems. A large portion of the New York City Subway has a 4-track layout, outer two for local trains, and inner two for express trains (on lines with three tracks, the express track provides one-way service, reversing direction as needed). This has also been implemented on Philadelphia's Broad Street Line, on parts of Chicago's Red Line and Purple Line, and on two small parts of London Underground, namely certain sections of the Metropolitan line and the Piccadilly line. Several variations of express services (e.g. semi-express, limited express) are also a feature in major Japanese railways, and on line 1 of the Seoul Metro.

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