There are about a zillion of them. "I've Been Working On The Railroad" is the most famous I'm sure.

My favorite is Marty Burke's version of "Fast Freight" by Terry Gilkyson. I couldn't find it on youtube but here's Terry Gilkyson's daughter Eliza's version (much different in feel from Marty Burke's version): https://www.youtube.com/watch?v=Sin3FeAQAws (fixed link, had Kingston Trio version earlier, oops).

Added: Found Marty Burke's version! It's been so long since I've heard this!! https://www.youtube.com/watch?v=G8y2iIzk6dw&t=1336s

"Riding On The City of New Orleans" is another one. I mostly know it from a version with rewritten lyrics inspired by James Blish's science fiction series "Cities in Flight". New Orleans, the city, is literally launched into space.

I thought of "America" by Simon and Garfunkel but it turns out to be about a bus ride rather than a train ride. Oops.

Your friend should see the movie "Mystery Train". It's great. Also read the short story "The Hell-bound Train" by Robert Bloch. We need a song based on the Robert Bloch story, which won the Hugo Award for Best Short Story of 1958.

Added: aha! The Bloch story was inspired by an actual song from 1910 (https://balladindex.org/Ballads/R599.html)! Here's a version by Dick Flood (https://www.youtube.com/watch?v=L85ciHPwDf8) and none other than Chuck Berry did a version titled "Downbound Train" (https://www.youtube.com/watch?v=4zCWJNILXUg), maybe because Berry's label wouldn't let him say "hell".

Here's a half hour podcast of a spoken-word reading of the Bloch story. You might want to skip the first two minutes, which are the podcast intro: https://archive.org/download/MindWebs_201410/046TheHell-boundTrain-RobertBloch.mp3

A now deceased friend of mine wrote a parody of "Song of the Shield Wall" about the history of the NYC subway system, but I don't think it's online anywhere.

Here's Leslie Fish (RIP)'s "Grain Train", based partly on her experiences as a railroad yard worker: https://www.youtube.com/watch?v=cRvJ2xgHt0E

Casey Jones? Out there somewhere, I'm sure you can find it.

Peter, Paul, and Mary, "500 Miles".

Oh how could I forget "Charlie on the M.T.A.". A classic. https://potrzebie.review/charlie.html

Tom Lehrer, "The Subway Song": https://www.youtube.com/watch?v=eQKA8UUH2yI

Dubliners' version of "Paddy on the Railway": https://www.youtube.com/watch?v=4kh_O2eyfX4 Again I prefer Marty Burke's version, which starts out livelier. Added: Found that too! https://www.youtube.com/watch?v=YnKjP5cywpo part of a 3-song "Canadian Railroad Trilogy". Someone has uploaded all the tapes of his that I lost decades ago!

Oh this one's important. You're bringing back so many memories. Shadows on a Dime by Ferron, title track of an absolutely intense folk album from 1984. https://www.youtube.com/watch?v=hMvnfBwv_l4

Bob Dylan's album "Blood on the Tracks" sadly doesn't contain any train songs as far as I know.

I'm not that big a train buff but I can understand the wish for a playlist. We almost need a genre of "train shanties" to go along with sea shanties. Sure, ping me with a list!

Added: aha, there is a Wikipedia category. That sort of spoils the fun, but: https://en.wikipedia.org/wiki/Category:Songs_about_trains

Ok, memory jogs from that category. Locomotive Breath by Jethro Tull is great. The category mentions Railroad Bill but the version I'm familiar with is Andy Breckman's. It's funny as hell but barely mentions trains: https://www.youtube.com/watch?v=msAuWlPZuAY

This has been fun!