Progress by fiat
The Obama administration is considering requiring US car makers to meet a CAFE requirement of 62 MPG by 2025. That is, of course how progress usually works: A beneficent, wise, all-knowing, government authority makes a decree, and the world magically changes to accommodate the desires of our political overlords.
Of course, it’s perfectly possible to make 62 MPG cars now. They just have to have tiny engines, and be extremely small and light. Who wouldn’t want that?
On the other hand, maybe steam-powered vehicles will make a big comeback.