Possible Clues:

• New York rail and bus inits
• N.Y.C. org. that operates 24/7
• NYC commuter letters
• Kingston Trio hit about Charlie
• Kingston Trio hit with the line "He may ride forever 'neath the streets of Boston"
• Letters on the A train
• It might help you get to Carnegie Hall, for short
• It runs the LIRR
• Letters on N.Y.C. trains
• Staten Island Railway inits