Back and forth I got about 48 mpg. Not bad considering I was going 80-90 mph most of the time. There are some parts in the desert which must have some big nice person tail wind. I'd be going mph and incredulously look at the mfd showing 99.9 mpg, and this would be 5-10 min blocks of time. No it wasn't downhill either. There was also a 20 minute block when coming south on the 15 before san bernadino where there'd be a small downhill grade and I got 99.9 mpg most of the time.
I bet it was wind. Going up to Billings, MT from Denver I got about 48 each way with a fierce cross wind blowing much of the time and the AC on (this was in late July and WY and MT were having highs just over 100 degs). I think that I'd have done somewhat better but the bloody wind was aweful. Judging by the way the grass was blowing I'd guess the wind was at least 20 kts gusting up to 30 or more at times. I was pretty disgusted with 48 mpg but I guess that's pretty good given the conditions.
Gosh, don't you love the mileage RANGE of the Prius? I can go from LA to Sequioa National Park and make it to Yosemite with still spare gas! Love this car.
