1.   Boston has the oldest subway system in the US.

2.   Mitchell visualized a hormonal flow chart that resembled a metropolitan subway system, all lines headed for the downtown station.

3.   Near the window, he put up a framed map of the New York City subway system.

4.   The city had built a great water-supply aqueduct to the Croton River and was imagining its future subway system.

5.   The Metro subway system was operating only a limited schedule of trains, on portions of its system that are underground.

6.   ...the Bay Area Rapid Transit subway system.

7.   Among its projects were the underground areas of the White House, the World Trade Center and sections of the New York subway system.

8.   An orange ring inside the carousel acts like the third rail in a subway system, carrying electronic data to the computers.

9.   And beginning on Wednesday morning, extra security officers were on duty throughout the subway system.

10.   And consumer buying slowed after a cult released poisonous sarin gas in the Tokyo subway system, killing more than a dozen commuters.