Mileage on first road trip

Speed kills the mpg's on the Prius, as it does with any other car. Also if you are on a road trip you probably have the Prius loaded down with gear and people, so hauling extra weight will hurt mpg's as well.

As others on here have found as well, the use of cruise control can hurt mpg's as well.

You might want to also get on Fuelly for better tracking of your mpg's, and let others learn from your trip. Your homepage on Fuelly gives a nice snapshot of your fuel use. Mine: The Grey Ghost (Toyota Prius) | Fuelly

 

Cruise control can hurt MPG's, but at the same time, I'd trade that MPG loss for less driver fatigue, depending on how long in duration your travels are.

 

I am one for CC use too. I love cruise.

75 mph AVG is fast. I noticed you mentioned 85 mph, many of us do not drive that kind of speed and it is why you see some folks with much higher mpgs. I try to set my cruise at 61 on the 70 mph interstate roads; this time of year I have been 60 + mpgs round trip of several 100 miles. my avg speed usually will be in the mid/high 40s because of stops, slower suburb roads when nearing destination and leaving destinations, etc.

I can't imagine many other cars getting 37 mpg driving down the road at 85 mph

 

+1
Basically you determine what mpg you get by choosing how fast you drive. True for all cars, perhaps more so for the Prius. Plus with the Prius (as for most hybrids) the mpg displays make this effect more visible to you.

 

On long trips I use cruise control at least 90% of the time.

Back in 1994 I had a 1994 Civic Hatchback model VX (the high mpg
model), it had no cruise control and on a trip from Portland Oregon to LA
my right leg was quite sore, and I swore than I would never
buy a car without cruise control no matter how good the
mpg's were, by the way that Civic was good for 50 + mpg.

 

In the past I used cruise control and did better mpg's with it than without, the opposite of my experience with the Prius so far.