I just got back from a 2300 mile trip from Atlanta GA to Rhode Island & back in my 2013 Prius. I am amazed at the mileage I got on the trip. I averaged 54.1 mpg (display) on the trip north and 52.5 (display) on the trip back south. I drove between 60-75 mph both ways. I am guessing the lower mpg on the return trip was due to the cold temperatures (teens to 40's) on the return trip. The only thing I didn't like about the trip is the nav doesn't give the direction of POI's and you can't enter them while moving. Small price to pay for such great mileage.
You are right...the mileage is great on the highway. Try staying at 60 MPH and your mileage will be in the mid to high 50's. Don't hold up traffic. I do this if traffic is light. The Prius is a amazing car.
