Radetzky March
I like my fantasy with a heavy side of dystopia, so the long run lack of sustainability in a steam-powered society is something that I think makes for a very interesting and realistic fictional universe.
The second law of thermodynamics strikes again! And societal oppression, I suppose...
Radetzky March
Perhaps a coil (like a watchspring) could provide the initial motion to a vehicle, and further power could come from an electrical battery which recharges itsself from the rotation of the axles?
You might be interested in
this. Oh, and they've tried the auto-charging battery thing. Sadly, it doesn't work.
Horatio Crane
Dark Matter is purely theoretical.
On the contrary!
(And sorry if I sound like a pedant, but seeing "theoretical" there made me cringe a bit. I kindly exhort you to use the term "hypothetical". Calling something a theory, in scientific parlance, actually means that it's a well-tested, well-proven explanation for the workings of the world; for some reason it's come to mean something different in the popular mind.)