After 3 winters, and all previous legacy vechicles, I am convinced ethanol kills my average in winter (Thanks for givings us ethanol in the winter). Driving Prius for field service, my usual trip distance is 16. My usual summer average of 50 drops to 42 or so. And then I get 40 hauling to ski areas. Ethanol sucks, except for NASCAR...
My summer average using ethanol is 51.3 MPG with a winter drop like that too. Focus on the average, especially since Prius does much better than average anyway. .