I can't imagine why simply crawling down a long hill would return that sort of mileage. The heater shouldn't demand *that* much fuel-burn at 34 degF, unless you were trying to keep the cabin at like 80 degrees. Heck, once the cabin's warmed up a bit I generally turn the climate system OFF, and a little bit of heat leaks out the vents anyways which keeps things quite comfy. On a stretch like that I'd probably do several bars of 99.9mpg, popping to neutral on a regular basis [such as when stopped or just slowly drifting downward] and only let the engine run when I actually had some room and a need for acceleration. . I regard this as fairly anomalous; the car should do better than that even without my particular OCD piloting style, and now I'm wondering what your corner parameter was that caused it. . _H*
Sounds plausible to me if he was going under 10 mph generally, with lots of stops and starts, and not warm enough for any electric mode. I've gotton that low in traffic jams in summer on flat roads, where I needed the AC on.
Anytime you run the AC you burn gas. If you are sitting still and not moving it counts as 0 mpg, and doesn't really matter what kind of car it is. When I had the bad mpg I moved about 1 mile per hour, in a big traffic jam. It was hot so I used AC and burned lots of gas.
Sorry, I meant the original poster, we've all been taking our guesses, I would like to find out which, if any are right.