I think this is a very interesting question.
Just read an article by Elizabeth Kolbert in the New Yorker. It's a book review -- actually a couple of books.
Auto Mania by Tom McCarthy http://www.amazon.com/Auto-Mania-Car...4394129&sr=8-1
“Zoom: The Global Race to Fuel the Car of the Future” by Iain Carson and Vijay V. Vaitheeswaran http://www.amazon.com/ZOOM-Global-Ra...4394277&sr=1-1
It now seems clear—and both “Zoom” and “Auto Mania” present a compelling case on this point—that car design could be radically improved. Already the technology exists to more or less double fuel efficiency. (A great deal could be accomplished simply by trimming the weight of the average vehicle, which has increased by almost thirty per cent in the last two decades.) The failure of the Partnership for a New Generation of Vehicles notwithstanding, tripling fuel efficiency also seems feasible. Such gains would have a huge impact in terms of oil consumption—passenger vehicles in the U.S. now account for forty per cent of the country’s oil use, and ten per cent of the world’s—and greenhouse-gas production.
"But improving gas mileage will take us only so far. Once the Chinese and the Indians really start driving, doubled or even tripled fuel efficiency won’t suffice. This is why Carson and Vaitheeswaran regard the Prius merely as a stopgap: the true car of the future has to accommodate everyone, which is to say six and a half billion, soon to be nine billion, people.
"Ultimately, designing the car of the future is such a daunting challenge because it’s bigger even than cars. As anyone who owns a BlackBerry or a cell phone or a flat-screen TV knows, technological change, when it comes, can come fantastically rapidly. But when we charge our video iPod nanos we are drawing power that, for the most part, is still generated as it was in Thomas Edison’s day. It’s true that hydrogen cars, which the Bush Administration and the Big Three claim to be working on, don’t need gasoline—the “freedom” in FreedomCAR is supposed to represent “freedom from dependence on imported oil”—but they do need hydrogen, which has to be produced using energy from somewhere. If that energy comes from, say, burning coal, as nearly half the electricity generated in the U.S. does, then the puzzle hasn’t been solved; it’s just been rearranged. The same catch applies to plug-in cars and cars that run on ethanol. (Ethanol made from corn takes almost as much energy to produce as it yields.) If someone, somewhere, comes up with a source of power that is safe, inexpensive, and for all intents and purposes inexhaustible, then we, the Chinese, the Indians, and everyone else on the planet can keep on truckin’. Barring that, the car of the future may turn out to be no car at all."