Cargo trains are hilarious and have some fun bugs and features tied to them. Aside from the fact that you can interact with most things on the floor when you're on them and that you can put crates/lockers/vendors on them with whatever you please loaded inside, you can even put on shield generators.
Grab the shield generator + capacitor and
put them on the train, with the generator being closer to the tug. All objects turn in the same direction as the trolley when you move, so this allows you to connect the shield. Unwrench and wrench the shield generator itself to make it realize the capacitor is attached.
Operate as normal. The shield will
stay up as long as the generator itself doesn't fail, even if you move the train. This lets you build awesome battlewagons and throw up a shield, even when you're moving, although you will probably be lynched by an angry mob of roleplayers and admins when the shield fails.
You can do the same thing with
emitters and can even snip the wire and turn it on/off at will. The only problem is that it will always point at the front of the train unless you make a turn and it can
blow up the tug. And, to top it all off, you can take the emitter off the train as if it were normal cargo and run around with an active, mobile emitter, fucking everything up and getting shot in the back. This one
will get you banned/gibbed/your shit deleted, if the previous one didn't.