> As a result it becomes more cost effective to upgrade the road grid than to build enough public transportation to eliminate it.
I doubt this is actually true. I think most people underestimate the real recurring costs of roads and cars put together. In fact, I suspect that is the real reason they are the primary transportation mechanism in the US: more expensive roads and the need for cars / gas makes more businesses dipping into the pie needed to support this infrastructure. This in turn means more political clout. It's a pretty safe bet in the US (not ruling anywhere else out here) that any solution to any problem which costs more will likely be adopted by political parties (and pushed by businesses/interest groups).