MPH and MPG

Draheim--
I just remembered some stuff that might help you do what you want.
IndyKing is a guy who used to be on PriusChat (he gave up his Prius because of lumbar support issues and other stuff). He had an interesting driving pattern--a boatload of trips from Indianapolis to Madison, WI and back. His pattern was basically a lot of interstate driving, and a little slow bit at either end.
Among his last messages to PriusChat was data on:
A bunch of his trips, including:
Average Speed of the trips (which varied mostly on the basis of interstate traffic and road construction)
Average Air Temperature of the trips
MPG of the trips.
From this he wanted to figure out the relative importance of speed vs. air temperature affecting MPG.

If you search for messages from IndyKing, you should be able to find it quickly.
You can use his data to correlate MPG and MPH, or, as he hoped, to do a regression analysis to look at the relative importance of average speed vs. temperature on MPG. I'd really like to see that, but I don't have the software or the statistical chops to do it myself.

This should yield some relatively high correlations--which may be valid only for the particular driving pattern IndyKing had.

However, given the very convenient distance between Indy and Madison, it will give you a sense of what happens with about a tankful of gas.

 

I commute about 85 miles (total) over very flat freeway. For two days, I commuted at about 50 MPG, and the Prius read 61 MPG, for an actual of 57.

I filled up and repeated, with the cruise control set to 70 as oftenas possible. Result was about 54, which is actually 51 MPG.

I think my generally high mileage is because I drive carefully, avoiding rapid acceleration/decelleration.