A rapid transit rail transport system, or a train in such systems, generally underground and serving a metropolitan area.
An urban rapid transit rail transport system, normally with lighter track and light trains (i.e. an S-Bahn or similar), or a train in such systems.
A metropolitan area.
metropolitan
A group of railway tracks running parallel, allowing one track to be used for each direction (a double-track railway line), or allowing segregation of fast trains from stopping trains (a four-track railway line).
A railway track; a pair of rails on which a railway train runs.
An organization that runs a railroad.