One of the greatest folk acts of all time.
They recorded M.T.A., the story of a poor soul named Charlie who failed to bring the correct fare (the fare had gone up from ten to fifteen cents that day, and he only had brought a dime with him) with him before getting on the subway. As a result, he was unable to get off the train (fares were collected upon exiting the train), and forced to ride the rails forever. (For those not familiar with Boston, MTA is Massachusetts Transit Authority, the local transit agency.) It's now the MBTA, for Massachusetts Bay Transit Authority.
It is possible to take the route in the song, but remember that Scollay Square is now Government Center (yecch!). (The full name is Government Center at Scollay Square)
Although you can get to all the stations, you can't take the same route as the Orange line now runs through different stations then when the song was written.
Originally a political song in support of a candidate whose platform included no fare increases. The line "Vote for George O'Brian" being a clue, along with the intro.
And kudos to Boston for having the most colorful subway trains :-)