If you want to know how screwed we are, consider this- for about 20 years Europeans have been making modern cars that get around 60 mpg. The American auto industry has hid behind "safety regulations".
Now there is vague talk of maybe getting 40 mpg with American cars, or even (be still, my heart!) raising the CAFE to 30 mpg. Well, while we're doing that, the Europeans will be going for 70 or 80 or 90 mpg.
Americans are saying, well, maybe automatic guideway systems in the road will substitute for mass transit, because the cars will move ever so much faster.
But if there's any rational place for cars in the modern economy, the Europeans will be cleaning our clock with gas mileage double ours per capita. And it's not like they lose this advantage by the amount our population exceeds theirs- on the contrary, if we have more people, we have more marginal expense.
If we can't wake up and smell the coffee, it's not going to be pretty.