On flat freeway, cruise control at 65MPH, no traffic, no a/c, what MPG should I expect?

On my first drive after purchasing my Prius, I filled the tank and drove it to Vegas using cruise control at 70. I averaged 56 mpg (on trip computer) on that trip, which made me very happy. However, there is a lot of mountain terrain between LA and Vegas and I've always found hills to help my mpg. And when I hit some annoying stop and go traffic, my mpg actually goes up, thanks to the traction battery.

To answer your exact question, I would expect 57-58 mpg on a long drive, which involves a round trip (trip computer, not calculated). Highways in my town often have a 65 mph speed limit, although I'll drive 3-5 miles over to compensate for the speedometer error. Short trips on a cold engine kill my mpg, as does the initial entry onto the freeway. Extra passengers lower my fuel economy more than I would have thought.

 

i would think 50mpg isn't out of the question.

 

Have you checked out Fuelly? Seems to say 2015 Prius III runs 46-47 avg. Highway should be a little better.

I believe Consumer Reports measures 55 MPG for a Gen3 Prius Highway at 65 MPH.
Keep in mind our DMV area has reformulated gasoline, which is probably a few less MPG than non-RFG areas. Not sure what fuel Consumer Reports uses.

 

Before I bought the Prius, I was impressed by reading an article stating that the car was reportedly getting 60 at 60. Meaning 60 mpg at 60 mph.

 

For 65 or for any other reasonable street or highway speed, see Bob's chart at the top of this thread.
Updated MPG vs MPH chart | PriusChat

Or see Uncle Wayne's chart over at CleanMPG.com:
Steady State Speed vs Fuel Economy results | CleanMPG

 

Interesting that there's a significant difference between the two at 70 mph. 52.5 mpg vs 45.5 mpg.

 

Do note that the Prius gets -worse- mileage on the highway than in the city. Some of the posts above seemed to imply it would be better.

 

When I was driving Gen3 I never got above 60mpg. Overall average after 3 years of driving was 52mpg. It was always better driving in city compared to driving on highway. I once got low 40mpg on highway driving at 75mph or above.

 

approx 55 mpg. i do a fairly flat 30 mile highway drive everyday. i go about 65 to 70, no more. I use a/c as well. I always average about 55 to 56 actually calculated when i fill up. Granted that does include some non highway miles as well. but for the most part its approx 75 to 80% highway at 65 to 70mph

note that air temperature place a pretty big role in mpg as i understand as well. so everyones chart is giong to look different. In the end i think a resonable expectation is between 52 and 55 on the highway at around 65mph

 

Note that this is an artifact of the different, artificial fudge/derating factors thrown into the EPA formulas. Real life drivers in real conditions may, or may not, see it. But don't read too much into this CITY > HIWAY labeling phenomenon.

 

I don't think it's "artificial", I see it all the time. It's caused mostly by air drag, which increases as the square of speed as I recall.

Best mileage that I see is at around 70 km/hr (about 45 MPH). On certain winding secondary highways in the mountains I easily beat the govt. rating. You wouldn't think it possible going up and down steep hills, but it's real measured numbers. Limit is 80 km/hr (50 MPH) on the roads I'm talking of.

On the only roads around here that meet the OPs conditions if you traveled at his requested speed you would be run over!

 

which ball park are you in?

 

Good point. My city mpg is worse than highway when there are a lot of stop lights every block during rush hour and there is a line of cars behind me, wanting to jackrabbit start and stop.

OTOH, my best mpg comes from city driving when I'm driving on empty roads during the early morning or late night. I can time the lights better, drive the 35-40 speed limit, all while doing a lot of coasting. Then, I can hit 60-65 mpg on 30 miles round trips.

 

Past experience shows that there are a few variables between cars that can affect fuel mileage.

Running weasel pee gas over the years, I got on average 52-53 mpg at 65 mph.

Cleaned out the fuel system with a bottle of Techron and after a few tanks of Top Tier gasoline I now get around 56 mpg at 65 with the AC running. A couple weeks ago I got 61.3 mpg running the Interstate with the AC running and the cruise control set at 55 mpg. That was with a calibrated Scan Gauge not the funky gas mileage gauge built into the car.

 

After the CAFE test cycles are run, the numbers are derated by different empirical fudge factors: 10% for City, 28% for highway.

Since Model Year 2008 (in the U.S.A., later in Canada), more things are thrown into the formulas, but the above fudge factors are still there.

 

That is my experience as well. If I stay off the highway and stick to our 45-50mph back roads, I get 50+ all day. But our regular commute is 70mph hilly NH & VT highway so our lifetime average is mid-40's.

Our Ethanol-laden gas here doesn't help, either.

 

I would say the problem with the question is "expect".
I think it best for newer Prius drivers to simply learn the vehicle and drive with little expectations.
The best way to know what your average MPG will be in any situation, is to drive that situation and become familiar with what MPG you can expect.
My experience with The Prius was that it was an excellent highway, long road trip vehicle. In the situation the OP outlines I would easily expect 50+ mpg. BUT...I wouldn't worry about it.
I would say if you feel it necessary to have a baseline? fuelly.com lets you look at reported averages for Prius for each year.

I think sometimes people are optimistic with their reporting. But it's a good baseline. Which brings me back around to the best information? Is the reality you discover for yourself.