What traffic jam? Oh, that big city thingy, eh?
I really, really don't believe we can improve fuel efficiency any farther. We are already at the point where we really maxed the amount of energy we extracted from gasoline. There is no way we can hit 100% fuel efficient, perhaps we are already at upper 90%
Same concept with furnace, have you seen 100% fuel efficient? EVEN electricity, because there are energy loss during transmission, so can't hit 100% with electricity. X amount of fuel comes out of mechanically or other form of energy will never exceed its maximum available energy. There will always be a waste of energy, regardless how hard we try. Now, you said about putting men in space, it requires ENORMOUS amount of energy to get them out of Earth, don't forget that.
Same concept with money, you can't buy more if you don't have enough money.
Everything has its own limitations no matter what.