I need to build an underground tram system.

[Green_Elite_Cab]

I did consider it, but I don't know how good or cheap it would be, and I definitely don't know if it can include moving parts. Can they print a train that's over 5 feet?

I'm not sure, but why not try? You can do pretty well with a smaller scale anyway.

If you have to make your own, you could also just build a "master" from scratch, and cast with resin plastic and RTV silicone rubber. Alumilite is a good brand for this. You might be able to make multiples that way.