File under the preceding post
Without doing any really controlled experiments, I have noticed a perceptible decrease in mileage when using my car's heater/defroster in the deep winter months. Kind of odd, but cold decreases fuel efficiency in inverse proportion dependence to my feelings of guilt. So when you see people bicycling in below zero weather and start muttering, remember that guilt is a transferrable commodity. Guilt can be neither created or destroyed. In theory, guilt leaves my pedalling brain and enters the nearest passing motorist.
Then we find the disturbing yet entirely predictable outcome for Prius gas mileage. That the energy efficiency flaw in hybrid vehicles turns out to key on heater or air conditioner use makes some intuitive sense. The fact that poorer gas mileage vehicles show less relative impacts on heater use than higher gas mileage vehicles should really come as no surprise. The finding indeed sucks, but then again you can't argue with the math.
Watch for the guilt-free Prius drivers next winter. They will be the ones that turn another kind of green. Either that or they will decide to drive with a few extra layers of clothing.