Line 4 of Chongqing Rail Transit is a rapid transit line in Chongqing, China.

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.