NEW YORK (AP) — New York City's subways — the nation's biggest mass transit network — serve more than 6 million daily riders who depend largely on a signal system that dates back to the Great Depression. Wynton Habersham, the MTA's chief of signals and track operations, recently led an Associated Press reporter and photographer on a walking tour through some of the 22 control "towers" — as the dispatcher spaces are called, though they're buried deep beneath the streets. In the cramped, worn-out Greenwich Village tower, MTA workers monitor light boards that show train locations and movement. A massive cabinet is arrayed with levers to move switches through a warren of electrical connections to relays that were cutting-edge technology at the same time as the Hindenburg airship. Amid peeling paint, rusty stairs and old-fashioned metal cabinets is a labyrinth of digitalized panels and switches that automatically relay signals in the tunnels, tracing both direction and speed without human help.