Okay, I just watched the movie and did some more checking. According to the IMDB, the stock elevated scenes are of the Third Avenue El in New York City. Pretty interesting how they blended the scenes together, especially the moving background. Looks like they built a platform where people were getting on and off. Where the guy leaps from one car to the other sure looks like the PE elevated structure.

My guess is that the tunnel scenes were filmed on a soundstage using sets built to resemble the Chicago tunnel system. The walls look like plywood sprayed with a concrete looking coating. The freight motor looks more like a mining locomotive than what I've seen of the tunnel motors. And the freight cars could have been built on the frames or trucks of mining cars. That's just my theory and I don't have any evidence to back that up.

At least this has been educational as I had no idea that LA had stockyards.

BTW, here's a somewhat dated website on the tunnel system:

https://web.archive.org/web/20040814082 ... nnel1.html

Most of the Union Station film was shot in LA. “L” car interior seem to be a studio set-up, probably generic period cars used in many films. Some stockyard scenes were also shot in stockyards near LA.
But a lot of Chicago L exterior shots as well as the tunnels were shot in Chicago.

Here is a link to the details.

https://whitecitycinema.com/2012/06/25/ ... n-station/

“Although set in Chicago, most of it was shot in Hollywood with Los Angeles’ iconic Union Station standing in for the title location in the Windy City. .... However, at least some prominent location work took place in Chicago; the movie’s first third features an exciting daylight chase between cops and kidnappers on the Chicago Transit Authority’s now-defunct Stockyard Branch Line and the the final action climax takes place in the Chicago Tunnel Company’s underground railroad tunnels.”

Been years since I watched this film, and seeing as Internet facts support both sides of this argument I located a CD and took a closer look at the tunnel scenes.
I was willing to think with all the miles of tunnel, some sections could be larger with squared off ceilings. However the width of the cars and gauge of the track are too wide. Chicago’s gauge was 2’ the film looks closer to 3.
Can’t speak to the actual elevated exterior scenes as I’m not that familiar with the old stockyard L.
Seems that the makers of this movie went to great lengths to not shoot a film about Chicago in Chicago.

I agree with you about the effort that went into shooting a "Chicago" movie in LA. I wonder why they just didn't move the setting to LA since it had a reputation as a crime noir location at that time?

To add another piece to the puzzle, the Los Angeles Railway (3'6" gauge) sold a number of cars to Lasky Studios in the 1920's. These were single truck work cars that had been rebuilt from open cars. Lasky later became Paramount Pictures, the producer of this film. So, could the tunnel cars actually be these LARY cars rebuilt by the studio to resemble a tunnel motor and two freight cars?

Because then they would have had to pay someone to re-write the script. The thing with "B" movies, and I think this qualifies as a B movie, was cost. If they can save money by editing stock footage, they will, even if not 100% correct, who is going to notice? The same still goes on today.

If the scene is tight, no grand vistas required, filming on a sound stage is always going to be cheaper than on location. Today they just do CGI.

So, they finessed the Union Station shots in LA Union Station, and the elevated shots with a combination of stock footage and close shots on P.E. and they are going to move a whole production unit to Chicago just to film the tunnel? I think not.

The whole movie is a study of film making on the cheap, and is actually quite a good job. I'm really surprised that after all that effort, they flub it by having the characters disembark from a P.E. car on the street. All I can figure is they blew a shot, or forgot a shot, and had to do a quickie very late in production.

"Union Station" is a pretty good example of film noir from that era. It is available for streaming on YouTube and Amazon. For a price of course.