I came across this interesting graph yesterday. (Sorry, I lost the reference where I found it. If anyone knows, please let me know so that I can give proper credit.) It shows the annual number of miles we drive, current as of April 2008. It tells me two interesting things.
1. We’ve doubled the number of miles we drive annually in the last 25 years, even though our population hasn’t doubled (actual population increase is on the order of 23%).
2. We appear to be at the point where increasing gasoline prices are affecting the amount we drive.
The recent downturn in mileage could be reasonably attributed to discretionary or “surplus” driving. It would be interesting to observe how the curve continues as gasoline prices increase and try to infer how much discretionary driving we actually do as a measure of our economic efficiencies.