Through train

A through train (also through service,run-through service/train) is a concept of rail transport (commuter rail, subway systems, and mass transit) that involves a change in the operating provider of the line, or a change in the identity (usually operational) of the line, at a specified boundary, on a regularly specified schedule (not random). This is usually accomplished through compatible infrastructure—identical track gauge and durability issues (although variable gauge trains do exist, they tend to be expensive), dimensions, curve speed and signaling compatibility, train station dimensions (to avoid damage to rolling stock), tunnels and bridge dimensions and maximum weight, and power requirements. The exact terminology (and definition) vary as usage; in the case of National Rail of the UK, a through train is one which may be used by a passenger to make their entire journey without changing trains.

Chinese cities operate several through-train services (simplified Chinese: 直通運行; traditional Chinese: 直通运行; pinyin: zhítōng yùnxíng):

Paris Réseau express régional:

In both cases, trains run contiguously, thus providing a one-seat ride across both SNCF and RATP networks. To achieve smooth network crossing, RATP and SNCF jointly designed and ordered specific MI 79 rolling stock (where MI stands for matériel d'interconnexion, French for "cross-network rolling stock.") Change of drivers was compulsory at network boundaries until 2008 when one-driver cross-network runs were introduced.

In Germany, such services are called Durchbindung.

Vehicles of Route 614P and 615P on the MTR Light Rail continue to run onto each other's route after they arrive at the termini in Siu Hong and Tuen Mun Ferry Pier, effectively running on a loop line in both clockwise and counterclockwise directions.

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