People will move and lifestyles will change if oil runs out.
In the meantime, government needs to put less empasis on free-ways and establish a more efficient way of taxing/charging the users of toll-ways. And the taxes/tolls should be srtuctured such that every time you pass a mass transit station, you get dinged with a toll.
In that way those who pass up the opportunity to take mass-transit pay either way. Those who don't have access to mass transit, aren't penalized.