Transportation is just a piece of the puzzle. The real problem, of which transportation is dependent, is urban design. Inexpensive fuel led to the wasteful practice of urban sprawl. Cheap energy also made it possible to keep making mistakes in urban growth and still be able to make unregulated sprawl work. Those days are nearly over.
If people live within a 15 min bike ride of their work and basic shopping needs, or better, work at home, then the issue of transportation almost solves itself. The ancient Romans knew this: its a very old insight. In Roman times, growth was carefully managed. With the exception of Rome itself, new cities were built to be only so big, as wide as a person could walk in an hour or so, and once that size was reached, they built a new city elsewhere, complete with all the basic amenities and arts that made it a desirable place to live and work. Satellite communities were not just housing tracts, they were complete planned cities interconnected by roads.
The equivalent solution today would use similar ideas as these ancient societies, but with the new addition of mass transit between smaller city hubs. Instead of one big city, you have lots of smaller ones. For cities to grow bigger, they would need a comprehensive mass transit system. These are all interdependent infrastructure necessities which are not fully addressed today.
To some extent, that kind of growth can occur spontaneously without direct planning, but obviously, only part of the time. An orderly spreading of the population through better urban planning would have an additional benefit: it would keep housing costs down, and ultimately, reduce labor costs. By not making one large city so critical to getting ahead or being happy where you live, you diffuse the demand for just one city.
That is where the state or even federal government could come in: they could create private incentives both for creating new planned cities, sensible mass transit, as well as encourage population to spread more uniformly, perhaps by subsidizing home building in newly defined population centers as well as creating tax breaks for employers there.
More exhaustive mass transit can be an interim solution, but even mass transit can get expensive once energy costs rise, since the cost of building and maintaining it is all affected by energy costs. Plus its not that flexible, - there is a big up-front cost. That's why the old ideas are probably the correct ones. Just build complete livable cities for which there is no commute you couldn't also walk or bike.
