>Here's something that surprised me but probably was well known to you quants:
>I bought a 2018 Camry Hybrid several months ago.
>This past weekend, to escape from snow and get some golf in, I drove to Santee, South Carolina - about 700 miles each way from here.
>I was also anxious to see what kind of mileage I'd get from the Camry with that kind of driving.
>The Camry has a sensitive meter that tells you what your MPG has been since your last fueling.
>With local driving around here it gets about 35MPG.
>I live about 10 minutes off I95 and my destination is even closer, so this was a straight line drive on the interstate
>The tank has a capacity of about 12 gallons.
>Same fuel - MOBIL regular, all the way.
>On the way down with below average traffic on I95, I averaged about 45 MPG. OK, but not great.
>Coming back though, I learned a bit more.
>I left with a full tank before dawn. Police in South Carolina ignore speeders, so you have to do almost 80MPH to keep up with traffic.
>I noticed almost immediately that my MPG was about 37.
>As I got into NC and VA where police issue summonses at speeds much over 70 MPH, traffic slowed down a bit and my MPG improved a but the overall tank MPG was a disappointing 42.
>I fueled below Richmond, VA and started with a fresh tank and the MPG was about 45 till I reached DC.
>At DC as things slowed down more and the MPG started approaching 48, I decided to try to find an optimal speed.
>
>At between 55 and 60, it got up to 50.8 MPG, while averaging in those earlier higher speeds. Just accelerating a few MPH dropped the MPG almost immediately, but dropping the speed didn't seem to help as much.
>
>When it got up that high, I also noticed that things like elevation changes start to come in to play.
>
>I suspect that with a fresh tank at 55 to 60 on relatively flat roads it would get up to 52 or 53 MPG
>
>Bottom line, speeds over 60 MPH are expensive and speeds over 70 MPH are VERY expensive.
>
>PS - my golf game needs a lot more work.

Aerodynamic drag varies as the square of velocity; double the speed requires four times the engine power to overcome drag. That's why your time at 70 or 80mph had poor economy results.

Ambient temperature differences could also cause some variation. If temperatures are warm use of air conditioning can reduce mileage significantly.

If you're willing to follow ("draft") semis at a safe distance you can see some significant improvements as well. Some people make a sport of so-called "hypermiling".

Hybrids offer no advantage over non-hybrids on straight interstate runs. In fact mileage may be slightly lower because the vehicle is heavier, with additional battery and electric motor weight. Hybrids are best in low-speed stop-and-go traffic; some have higher city MPG than highway MPG. They are great for taxi service. Vancouver has been an early leader in this, one enterprising cabbie used a P1 Prius. When Toyota found out they bought it from him for analysis and gave him a brand new one: http://vanmag.com/city/vancouver-taxi-driver-worlds-first-hybrid-cabbie/

My car has a similar fuel usage meter but I think it's a bit optimistic. I record the odometer reading and how much fuel I put in at each fill-up but I haven't yet crunched the numbers to figure out just how optimistic it is. Your odometer plus a trade-legal pump at your gas station will be more accurate than your on-board meter.