-- Last Updated: Oct-30-12 9:16 AM EST --
I'm on my second prius and my friend has one too. I also have a Honda Insight. With either one I have no problem staying closer to 50 than to 40 actual mpg on the highway if i drive normally with traffic between 60 and 70 mph. If i drive closer to 60 mph i get clost to 60 mpg. That's with nothing on the roof. With 2 surfskis and 2 guys and gear over a 1000 mile roundtrip last year i easily got 40mpg actual mileage with speeds around 60mph.
My wife drives our '08 Prius and she's consistently around 44 actual (46.5) on the computer. I used to track both her and my old '02 and they give similar results. With the In sight I'm getting 43 mpg actual over the past 28k miles in mixed driving - if it was only highway or suburbs it would be much better, what kills mileage is short trips on cold engine, of which I do a lot...Plus, I'm usually the fastest and one of the more aggressive drivers, not a traffic calming device like some like to drive -;) If I drive calmly and with the traffic flow, I beat the EPA by a considerable margin - but who drives like that in the Metro D C area ???
That said, Top Gear managed to average 17 mpg in the Prius being gunned down to the floor, where a BMW M3 did 19 MPG at the same speed, following the Prius. So, you could torture a Prius to give you well below the EPA rating average, but most people seem to be getting about 50mpg real mileage out of the 2010+ Prii (just check Fuelly.com, with hundreds of real people - don't take my word for it).