It's a great song, and a fascinating story. But I can't help wondering whether get the feeling the story came first, or the song.
Is this a traditional song which was actually sung back in the first half of the 19th century by people using the Underground Railway? Or is it a song made up in the second quarter of the 20th century by someone who felt that there ought to be a song about the UIndergrond Railway?
Where did it first come to light? And where did the first people identified as singing it get it from? (So far the earliest anyone seems to have tied it down on the Mudcat appears to have been the Weavers. And though that's a good site that Animaterra gave us, it doesn't look into those questions.)