A through train is a concept of rail transport that involves a change in the operating provider of the line, or a change in the identity of the line, at a specified boundary, on a regularly specified schedule. This is usually accomplished through compatible infrastructure—identical track gauge and durability issues, rolling stock dimensions, curve speed and signaling compatibility, train station dimensions, tunnels and bridge dimensions and maximum weight, and power requirements. The exact terminology 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.
China
Chinese cities operate several through-train services :
Passenger: Some trains from China's Guangzhou-Shenzhen Railway cross the border and run onto the Hong Kong MTREast Rail to Hung Hom, but these trains do not stop along its stations, because border clearance is only done in Hung Hom. MTR also operate trains from Hung Hom onwards across the border on the Guangzhou-Shenzhen Railway.
Several subway systems have through operation between lines. Although this is usually a service crossing between a somewhat arbitrary boundary between two lines.
Beijing Subway: Line 4 and Daxing line most trains from Line 4 through operates into the Daxing Line and all Daxing Line trains continue into Line 4.
Hong Kong MTR: Trains on MTR's Kwun Tong Line may continue to run onto the southern half of Tsuen Wan Line to Central if services on the northern half of the latter are disrupted. This is also a standard special service during peak hours. Likewise trains on Kwun Tong Line may continue onto Tseung Kwan O Line to Po Lam or North Point when service on the latter line is disrupted.
Nanjing Metro: some Line S1 trains through operate into Line S7.
Guangzhou Metro: some trains of Line 3's Main Branch and Northern Branch through operates. Normally, the Main branch operates trains from Panyu Square to Tianhe Coach Terminal stations, and the Northern branch operates trains from Tiyu Xilu to Airport North stations. However, some trains will through operate, running between from Panyu Square to Airport North.
France
Paris Réseau express régional:
RER A trains serving the Cergy and Poissy branches run on SNCF and RATP tracks.
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 Change of drivers was compulsory at network boundaries until 2008 when one-driver cross-network runs were introduced.
Germany
In Germany, such services are called Durchbindung.
Japan
Through services are regularly scheduled train services owned by an operator which runs over tracks which it does not own. Many urban railways in Japan operate such services to increase ridership, increase convenience and simplicity, and reduce time to destinations by eliminating transfers through seamless connection. One example is a Narita-to-Haneda service, which runs on four companies' tracks. Despite fewer new lines in recent years as the system is mature, more through services are proliferating to reduce cross metropolitan area connection time, at least in theory. A 2016 MLIT study has shown that minor train delays are quite commonplace in Greater Tokyo during rush hour, at odds with Japan's image of train punctuality. The reason for this is that the subway lines in particular are subject to heavier loads, and thus more delay as riders rush in at the last minute, and forcing final door closings to be delayed. The proliferation of through-services has only magnified the problem, as it acts as a double-edged sword, though convenient in not having to switch trains, central Tokyo delays increasingly cause a ripple effect to through services on suburban lines.
