After almost 1,000 miles of mostly highway driving during the Thanksgiving weekend, I was able to get my average mileage on the EVIC up to 20.0 MPG.
Unfortunately, the last 60 miles of bumper to bumper traffic dropped it back down to 19.4 MPG, but I never thought that I'd ever see 20.0 MPG. I used the cruise control set at 5 MPH over the posted limit and drove mostly at 60 or 70 MPH. I didn't have to slow for traffic about 90 percent of the time. Traffic was not bad at all for a holiday weekend.
By the way, the NAV proposed some funky routes when I first tried to use it. It would also sporadically decide that I was off route and recalculate. I ignored most of its advice, but took one of its apparently traffic condition based suggestions and am pretty sure that I dodged a parking lot on one of my regular routes. I decided to trust it after seeing it correctly identify some traffic accident based congestion in the middle of Pennsylvania. I'm looking forward to getting my iPhone docked on the dash so that I can compare its routes to the NAV's routes.