I suspect this increase is wholly due to lifestyle changes. More folks are moving to more remote suburbs. Their houses are far from the nearest school, grocery store, library, coffee shop... so if they need anything, they need a car to get to it.
If those remote suburbs were zoned a little differently to allow nearby services and if the population density was a little higher, you would probably see a reduction in annual auto mileage.
Of course, there is a phenomenon I describe as the "constantly-in-motion" individual. They live in their vehicles and -- particularly -- spend their time off going from one event to another... by car! However, I think the rising price of gas, plus the general efficiency of evolution, should cause this behavior to die off.