Yeah, no doubt you've noticed that "Peak Car" is making headlines on the FP lately. Unfortunately, Peak Car looks at the problem incorrectly, at an angle that's only going to perpetuate the problem (at best, just at a slower rate). It's not a car problem but a transportation problem - we need to look at Peak Transportation and prevent the inevitable gridlock regardless what form it takes.
Swapping individual auto transport for public transportation shrinks that gridlock, yes, but public transport is still highly vulnerable to gridlock. The causes of gridlock boil down to a very broadly spread community trying to commute from one disparate part of town to the other through a very small selection of corridors. Regardless as to whether those corridors are highways or commuter rail lines, the basic outline of the typical American city (like the classic L.A. example) clogs them up. And regardless towards road networks or public rail, there's peak practicality limiting those corridors - and it's a very small number.
A part of this is a failure of urban planning - planners only went so far into the future when extrapolating their population figures - but once again there's a practical limit as to how far this future prediction can go. Endless accommodation for expansion only creates an empty version of the same exact problem (see the nearly empty ghost boom towns of China). Neither does it change the fact that the infrastructure and city layout is already out there and frozen. People live in the out rings and work in the inner rings. Or not necessarily, but the point is that people work and live in such a way that long commutes by some means are necessary.
The really solve the problems of Peak Car (or Peak Transportation) a heavy rethink and outright rebuild of the very core of the American city is necessary. Now, this is what I figure is the best solution, but it is by no means an easy or cheap solution - then again, the problem's become so big an easy and cheap solution is but a fiction. Basically what this entails is to shrink the core of cities by building up, just like in Dubai, China and even right here in America, but with the idea that living and working be co-located so that a typical commute is just a few steps.
This isn't something revolutionary and really it's an obvious solution, but what makes it staggeringly difficult to implement is the fact that it requires major American hubs to be literally rebuilt from the ground up (actually, quite a bit below ground, even). That's going to require billions per hub. The traditional challenges of urban planners don't disappear either, just that road networks are largely replaced with pedestrian networks. They'll also have to figure out how to attract people towards living in such hubs, as well as being able to afford it.
So, yeah, it's very much a huge problem. But I don't think the current forecast of road and public transportation planning is going to cut it in the future either, and as I said, it may not be the easiest solution but the way I see it perhaps the best and the only one that provides real population growth solutions.