Basically, the point is that "the secret" to a vehicle with 300 mpg mileage isn't in some sort of special internal combustion engine that is much better, but rather in realizing that such a vehicle would have to be lighter and have less wind resistance than a moped, if it were supposed to travel at 60 mph.
How such a vehicle could carry 4 people is a mystery - let alone how it could carry the dog and a week's worth of groceries, or a trunkful of luggage. Those silly little electric bubblecars seen in Boulder and other "enlightened" places - they have too much wind resistance to make it. (And, they only have one occupant capacity.)