Stuart-not sure you have the resources or inclination, but it would be interesting to see the same sort of graphs for canada, where higher prices may encounter more price elasticity.

I know they drive more than Americans, due (I guess) to further distances.  Given that Vermont and Wyoming are highest VMT in USA (per your post last summer), and they had sharpest drop post Katrina, I bet there is a correlation.

Then again, there is (like in everything) a differnce between needs and wants. Perhaps Canadians just need to drive more (to get to work and grocery store, etc)

Canadians do not drive more than Americans.  In fact on a per registered vehicle (passenger) basis, Canadians drive around 20% less than Americans.  Most driving occurs while commuting or shopping, not travelling cross continent.  Canadians are a highly urbanized population and in general our cities have better public transportation and better land use planning, though that is not saying much.  Between 2000 and 2004, per registered vehicle mileage decreased about 1.5% in the U.S. and a little over 5% in Canada. Higher price may have something to do with this, but this requires an analysis of relative disposable income, changing employment levels, as well as more information on the availability of alternative transport modes.

In both countries it appears that higher prices are having an effect on demand, when the problematic is examined from the perspective of registered vehicles.

Transport truck mileage is a separate issue.

I use data from the Bureau of Transportation Statistics and from Statistics Canada.