Interesting point. My impression is telecommuting isn't really much of a factor - not many people, not many days, usually give it up before long. I wouldn't expect the changes in freight delivery to have much impact since trucks are a small fraction of total miles. The lines definitely look a little different in the last decade. However, one can also argue the era after 1991 or so is a long period with no oil shocks, and that might have to do with it. Not saying you're wrong, but hard to tell.

It seems useful to investigate aviation - it's transactions and economic activity, but removes the land use factors that seem like they'd come into play a lot in the highway mileage.

Transportation Energy Data Book says that aviation passenger miles grew at 4.8% annually from 1970- 2002 (ie significantly faster than GDP), but it was only 2.9% from 1992-2002 (pretty similar to GDP). I guess the earlier part of the curve was very much still in the adoption phase for airline traffic, and now maybe it has settled down to be similar to GDP.