A through service is a concept of passenger transport that involves a vehicle travelling between lines, networks or operators on a regularly specified schedule, on which the passenger can remain on board without alighting. It may be in form of either the following:A service where the vehicle travels between different lines, or systems of infrastructure, for example, a through train service between the mainline and underground railways.
A service where the vehicle changes its identity en-route without requiring passengers to alight, for example, a through tram service which runs as route 1 initially, then runs as route 2 for the latter half of the journey.
A Tokyu Corporation train on the Tobu Isesaki Line. Through service between different suburban rail lines are common in greater Tokyo.
In rail transport, track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks.
Fish-belly cast-iron rails from the Cromford and High Peak Railway
An early Stephenson locomotive
Triple gauge, from left: 1,435 mm (4 ft 8+1⁄2 in), 1,000 mm (3 ft 3+3⁄8 in), and 600 mm (1 ft 11+5⁄8 in), on display at the China Railway Museum in Beijing
A cartoon depicting the horrors of goods transfer at the break of gauge at Gloucester in 1843