I heard from a former employer that Americans use cars a lot because of the vastness of the country (our office handle the customer care of a car parts company). So that's understandable but yeah, it could have been reduced with more planning. If people just live near work, they can commute and then just use their car when going cross-country (I believe that's what they call travelling through states) or just take the train.
Unfortunately, the image of the American Dream seems to be a large house, with a picket fence and a garden. It's a nice dream but should also not forget that we are leaving the planet to our children and they should also be able to enjoy it like we did.