Lyric discussion by jhxetc 

Cover art for Daly City Train lyrics by Rancid

While I can't say for sure, it's most likely about someone that Armstrong personally knew. His lyrics are usually very literal.

My best guess is that it is about someone who was a drug addict and shunned by the general public but who Armstrong developed a personal relationship with and found to be a very beautiful person.

He says how low he goes it just depends, and follows that with shooting dope in the mens room. That's a pretty low moment moment in most people's opinions. However he follows that up with Have you ever seen an angel?...

I believe the song is about a real person who either died or disappeared, and Armstrong is writing a sort of homage to this person.