I like your definition, Alexandralaughing.(...) a song that uses trains as a metaphor for longing, going places, the transitory nature of life and relationships, (...)
I'm sorry Abter1. I also hope there is help in view for all of you.
What I mean by a train song is a song having a train for main topic and|or imitating a sound of a train. That may be a whistle, the particular rythm of a train on the railway, etc. This style came into fashion when the first railroads were built.
Taking a trip, you know what that meant back in the 70'? Version number 1 is like taking the last trip with Janis. Hear the sound of a train in the song. Elastic and smooth and hallucinogene. This guy is a genius.
Riding the H-train means being under the influence of heroin. Racing the midnight train, I don't know exactly, but it seems all of a voyage.