[Obadno]

The longest commutes most people seem to tolerate are about 45 minutes to an hour.

The mode of transportation does not matter and density does not matter thats about the limit people land on. So until a faster mode of transportation than trains and cars can get you from the farthest Exurb to your job they are about as spread out as they are going to get.

Now this does get a little warped as major Metro areas have multiple employment hubs and of course outliers of people willing to travel outrageous lengths to get their little slice of suburban (or rural) bliss. But unless its a smaller city with lots of room to expand outward like Boise or Odessa-Midland, id expect most of the top cities in america to continue their current trend towards more density.

Of course there is a cultural component too, from 1940-(even now in many places) getting your own little house in the suburbs was a big cultural push, id never discount a turn against urbanism like we saw after WW2 happening again sometime in the future.

But, things will still change a lot with the growing prevalence of working from home with modern communication tech which could see really odd changes in living patterns. There is no reason why you cant be a day trader or independent tech contractor working from a small town in Montana as long as you have a good internet connection and are willing to be up early. etc.

And of course if we get Jetsons flying cars, Futurama people tubes or teleporters then all bets on built form are off.