This report is from August, and it will, hopefully, be updated by January in order to determine whether or not Americans dropped below the 3 trillion-mile mark. I think this is a very interesting fact about modern American life.
The reason why I looked this up is because gas prices are falling. Despite the fact that we are in the holiday traveling season, there is less of a demand for gas (and so the price falls, I guess) and there are fewer Americans on the road. Gas could increase around Christmas time, but, even then, the trends show that fewer and fewer Americans are driving.
Why does this matter? Well, it's good for a few reasons--namely, environmental reasons. It also puts less strain on an already-crumbling infrastructure in the United States. But it means that people are spending less money at gas stations and at travel plazas and fewer people are connecting in person and are relying on social media even more to stay in touch. These aren't horrible reasons for or against, but there is something to be said for the fact that, when Americans don't spend money, this ripples through the economy. When Americans decide enough is enough, and abandon things like travel, motels, and restaurants in favor of staying home, that means tougher times for those businesses.
It looks like Americans have picked up the habit of staying home, or close to home. If this continues as a demographic trend, look for fewer travel amenities. People will just decide that they need to get out of that business.