[closeparen]

Car-oriented development seems to scale efficiently - bringing in a lot of new, cheap land - up until you hit the level of traffic that people will tolerate. Then it's done. New neighborhoods take too long to commute from. Densifying existing neighborhoods threatens parking, which people who live there still need, because they still live in an overall car-dependent metro. Overlaying public transit doesn't do much either, since people's origins and destinations are evenly dispersed instead of clustering around stations like they would in a real public transit city. Without transportation capacity there's no growth, and without growth it's a zero sum competition for existing homes.

You can get a whole hell of a lot further before you hit the physical limits of public transit network architectures.