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The Mexico City Metro is the largest and busiest heavy-rail rapid transit system in Mexico and second in North America, only behind the New York City Subway.
As of 2014[update], the system is composed of 12 lines denominated 1 through 9, 12, A and B, totalling 226.5 km (140.7 mi) of track length and 195 stations. Of all stations, 115 are underground (either in shallow box-tunnels or deep circular tunnels), 54 are at street-level and 26 are elevated.