I've been thinking about this recently. Public transportation really outshines cars from a convince standpoint only if the commute is set in stone, or if you live in a dense metropolis.
A car is a selfpropelled couch that gets you off the beaten path, which is a requirement for 90% of American sprawling communities outside of large urban centers. I can't imagine a train beating that without serious consolidation and centralization of populations which is already putting the cart before the horse.