For myself it is the money. Even though I could buy a car right now, I won't, because cars are money-eating machines. If I bought a car I would not be saving enough money to buy a house later on. It's simple economics. As a consequence however I take public transit, and give up a lot of freedom, to go where I want, as far as I want. And I still end up spending a fair bit on transportation anyways.

A small car that costs the same, or less, than public transit would enormously increase my freedom and everyone else's without compromising my desire to save my money for the future. For people who have large vehicles already, the small car can be rather constricting. However I have regularly seen as many as five fully grown people crammed into an econobox - so it is possible. The question is: will a Supermileage car have the same capacity?

Most cars on the road have just one person in it, which is very wasteful. So the 2-seat inline design of the Supermileage car is smart. One seat can fold down for a larger cargo space, and you get the best fuel economy 95% of the time. But there is not enough room for 5 people. Or if you have 2-3 kids there also would not be enough room.

It may be reasonable to have a commuter car with a passenger buggy towed behind for the extra passengers. To increase the towing capacity the passenger trailer would have its own engine and fuel tank, and you could have open communications between the front & rear compartments, like teleconferencing speakerphones. I've seen people towing similar buggies behind their bicycles with children in the back. More robust designs are quite feasible I think. In fact I think a loose trailer hookup between the car & buggy could be turned into a solid modular fixture with some work. The car and buggy would behave as one unit.

There are so many things that could be done, I'm just scratching the surface. After all, it hasn't really been pursued at all by the big automakers. I can only imagine what they would come up with after thousands of man-hours of engineering that they could compress into a few months time.