How come I didn't see the bar before. That looks amazing!
There's a few options we can do for making a train in BF2. The most obvious is to just make a moving prop. But since units can't move with moving objects, it'll be kinda buggy and the trooper will be doing the "collision shake". If the subway goes too fast, the unit could fall through the wall.
You could also make a autopilot hover vehicle (what's the term for that again?). But getting them to go the direction you want them could be a little trickier. I don't think there's a way to tell AI in vehicles where exactly to go. You can do planning and stuff, but it won't work in this case.
Another idea is to set up a hover vehicle with all passenger seats without a pilot (is that possible?). Then you would have an invisible wall following the hover vehicle, forcing it through the tunnel (which would need collision also). This is probably the easiest and best idea.
The last idea is to set a flying vehicle with flyersplinelines and an autopilot. You would have to set the maximum and minimum flying heights to keep it in balance. In addition to some collision on the walls to keep it going to far off. Its a little bit trickier.
I chose the subway trains and the stations. I dunno where I'm gonna get a track model and/or texture.
Unfortunately, these are all Train Simulator models. I'm going to have to contact the original authors and ask them for the models and textures in more universal formats.
Btw, where would the route and the stations go?