rapid transit

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An urban passenger transportation system using elevated or underground trains or a combination of both.

from The Century Dictionary.

• See transit.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A commuter rail system that combines aspects of an interurban railway with those of a subway, using a menagerie of pathways such as viaduct, tunnel, beam, cut and cover, trench, at grade, and others.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an urban public transit system using underground or elevated trains