This is completely off topic, but I've wanted to say this for a long time.
I bought a 2001 model Prius new in November 2000 and I now have 105,000 miles on it, so I would call myself an experienced owner. Not too long after I bought it a leading consumer magazine stated that their measured combined city/hwy mileage was 41 mpg. This is something that has stuck with the 1st US generation Prius and is still widely reported.
Let me just say that if our Prius ever averaged as low as 41 mpg, I would have it back to the dealer for repairs. In fact, I cannot recall ever filling up and getting below 40mpg. I have had as high as 51 mpg as measured by a fillup -- the display mileage is a good indicator, but not always correct, it has read as high as 54mpg which I do not believe.
As an engineer I know that in order for my mileage to be valid, I should reduce or eliminate as many variables as possible. Since I live in a small town, I always fill up at the same Chevron station (except on trips). Usually at the same pump so the angle of the car is the same. Another variable in computing mileage is the time of year. Gasoline formulation changes throughout the year -- winter blends are different than summer blends.
Oh, and don't forget that blasted ethanol blending encouraged by people who want to see their food prices go up. When I first got the Prius, the Chevron pump did not have a 10% ethanol blend sticker on it. A couple of years ago (or so) it appeared and the mileage promptly went down a couple mpg, never to come back up. Refiners here seemed to be late in adding ethanol because we get our crude from Alaska and the ethanol has to be shipped here.
But the blend is only part of it: that model Prius is appears to be highly susceptable to temperature.
My observations are that when the temperature is below 40F, the mileage goes down to the 43mpg vicinity. When the temperature is above 60F, the mileage goes up into the high 40s.
Most of my driving is at county road speeds, a bit of highway and a bit of 10-25 mph retirement town crawling. Our elevation varies from sea level to 250 feet. And I replaced the OEM tires that wore out quickly (we went through two sets way before 50K miles) with Les Schwab TOYO 800 Ultras several years ago -- the TOYOs supposedly have a higher rolling resistance than the OEMs, but I didn't notice any mileage differences. I keep them at 40 psi and try to check them once a month. A before you say that my speedometer/odometer is wrong because of non-OEM tires --Sequim just installed 2 traffic radar units in front of the high school to tell you to go 20 mph -- the speedometer matches the radar units displays.
All this is to say that the magazine ran some tests, probably in the winter with ethanol in the gas at an unreported altitude higher than sea level and forever pronounced it to be 41 mpg combined. They would be surprised to learn that I filled up last week and got about 47 mpg which is not bad for a 9 year old car in late April/early May.
Perhaps they should consider testing cars at more than one location and at different temperatures for a more accurate report.