[andybak]

"That's really just a negative externality of inefficient suburban development." Shouldn't public transit cover rural areas and small towns also? Or is the only way to get an efficient transport system to have the entire world living in huge urban centres? Personal mass transit could allow a much wider range of city sizes to be served with relative efficiency.

[thrownaway2424]

Mass transit doesn't need "huge urban centers" and indeed can and does serve cities of all sizes. What it requires, though, is a minimum density. You can't serve a small, sprawling city. You can easily serve small, compact cities. Compare, for example, the transit effectiveness between Zurich and Tulsa, cities of comparable population.