Construction of the 63rd Street Tunnel began in the late 1960s but service to the island did not begin until October 29, 1989. Although infrastructure projects in NYC routinely go over budget, this one was remarkable, with a $28 million initial estimate ultimately ending up costing $800 million. The final section of the tunnel connecting a previous dead-end in Long Island City to the Queens Boulevard line did not open until 2001.
At 100 feet below street level, this station is the second-deepest in the subway system (after the 180-foot-deep 191 Street IRT). The line also includes an unused connection to the BMT Broadway Line and the tunnel has a lower level that will permit Long Island Railroad commuter trains to come directly into Grand Central Terminal (the LIRR East Side Access project). (reference)
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