In my own personal experience, with all peripherals and creature comforts shut off, except radio, during the daytime... doing 55 mph, sometimes a bit less, hardly ever touching the brakes, and driving smooth, in "D", paying attention to changes in elevation and coasting down hill when you can... my best has been 6.1 to 6.3 miles per kwh, starting and ending at the same location and elevation for the drive.
It can be done, but you need freeway or interstate on polished concrete, Bridgestone Ecopia 422 Plus tires set at 45 psi, and very, very smooth and steady driving techniques, with traffic that is accomodating on freeways or interstate. I try to get way far back behind a big truck, so cars that come up behind me know I am not the one impeding traffic, I can't drive faster than the truck in front of me, so they go around me.
You might have some luck heading south on 101 or interstate 80 to Sacramento and back, but not in town, in San Francisco. Way, way too many herd mentality drivers there with poor driving habits, driving combative instead of smooth. Just too many people there.
