This is a really good point, and one I haven't given much thought to. My father lived about 5 miles from work and insisted on driving the same Suburban every day for 20 years. Thank god he drove two other people, but I was always frustrated that he chose to drive such a ridiculous vehicle on suburban (ha!) streets every day. His business partner chose to live an hour away so he could have a bona-fide mansion complete with horses and drove more fuel efficient and "sensible" small luxury cars (a cooper mini for a while, then a BMW 3 series).
Why complain?
Your father's driving left less of an "environmental footprint" than that of many smug Prius driving enviros, because he 1) drove very little and 2) car pooled.
I drive an old Chevy Silverado. If any smug enviro (and I know a lot of them in my job as an environmental engineer) ever questions my choice, I slap them upside the head with Math.
The Prius gets roughly 3 times the mileage of my truck. However, I drive my truck 1500 miles per year.
If the enviro weenie drives his Prius a typical 12,000 miles per year, he is having more than double the negative effect on the environment that I have. Unless you KNOW you are having less impact, you should probably choose to STFU and let the person make their own choice rather than go into enviro bitching.
But here's the real fact: Mileage is pretty trivial.
Your overall CONSUMPTION habits have far more effect on the environment.
I can't tell you how often I listen to some preachy enviro bitching about pickups, while shopping for tons of junk to fill her huge house- that has huge environmental costs in production and transportation, to say nothing of disposal.
Either that, or they keep their AC at 70-72 in San Antonio in August. I actually know a Prius driving enviro who does this- keeps her 3,200+ square foot house chilled like a meat locker, yet considers herself a die hard liberal protector of the environment- always bitching about trucks, guns, and how hard it is to make ends meet (with her $450 electric bill).