Secrets of the New York City subway system

The New York City subway system celebrated its 115th anniversary this week, and since its debut it has grown from a single, nine-mile line, to more than 800 miles of track and 472 stations, servicing around five million riders every day. Kris Van Cleave talked with historian Polly Desjarlais about some of the subway's secrets, and with Concetta Bencivenga, of the New York Transit Museum, about a true engineering marvel.

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