"They should always be viewed as estimates. We don't want consumers to view them as absolute values," Margo Oge, director of the EPA's transportation and air quality division, told the Chicago Tribune about the estimated MPG numbers that each new car sold in the U.S. bears.
Michael Karesh is trying to outdo the EPA. We often refer to the EPA's miles per gallon rating for cars not because they are incredibly accurate (they're not) but because they offer us some sort of standard to make comparisons with. Karesh, through his site TrueDelta, is trying to get a mpg rating for different makes and models that reflects real-world use. This means figuring in things like air conditioner use, traffic, landscape and more, factors the EPA eschews. He's doing this by asking user