TOKYO - MAY 11: Tokyo Metro Marunouchi Line station on May 11, 2012 in Tokyo. With more than 3.1 billion annual passenger rides, Tokyo subway system is the busiest worldwide.
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TOKYO - MAY 11: Tokyo Metro Marunouchi Line station on May 11, 2012 in Tokyo. With more than 3.1 billion annual passenger rides, Tokyo subway system is the busiest worldwide.