Consider that a cheap motorcycle can carry two passengers at about 70 mpg with no modifications. Consider that _bicycles_ can be made with fiberglass fairings that can be pedaled over 70 mph. (Air resistance is by far the largest source of drag for land vehicles at road speeds. Reducing this drag would shoot up the mileage of a motor vehicle enormously.) So, to make a very efficient car, one could reduce the size of a small motorcycle engine considerably, design a frame that places the passengers in seated tandem position, reduce the height of the vehicle above the ground, add a two-wheel front axle, and then cover the thing in a plastic or fiberglass bubble. None of this requires exotic materials and could provide a vehicle that would surely get well over 150 mpg and could get close to 200 mpg.
But no such vehicles are made because gas is cheap. That is the important fact, not the state of present materials technology or aerodynamics. If people ever drive these project cars it will be because the government _makes_ them, not because these vehicles "finally" become available from commercial manufacturers. And environmentalists know this.
Whether we should be made to get into such cars is the real question. But this question the environmentalists avoid since they realize that the overwhelming answer from the citizenry would be "no". So, for now, we occasionally get green-leaning news articles about clever ways researchers are trying to "solve" the problems of low fuel economy for passenger vehicles. That, at least, will leave people with the impression that there is a problem, and that we have to solve it somehow. *Sigh*