Possible Clues:

• Boston subway inits.
• Rail org.
• NYC's commuter org.
• 1959 hit based on the traditional folk song 'The Wreck of the Old 97'
• A-train org.
• Kingston Trio hit, 1959
• Where Charlie 'may ride forever,' in song
• Underground letters
• Kingston trio hit of 1959
• Charlie's endless ride, in song