Saving gas also uses earth-friendly operated machinery, such as biking, mass transit, and hoofing it. IMHO, I think the top 10 should take into consideration how often the contestant uses alternative ways of transport -- so in the meantime, the 90-day average punishes those who use a low amount of fuel over the course.
I know, I know, this is about the car/driver achieving good mileage in and of themselves, but for some, the bottom line is reducing emissions, overall.
I'll admit that I take useless trips which would put me in the lower classes (I just like to drive -- cars and driving is a passion of mine, and doing so efficienty is an additional interest).
RH77