I was sitting in stop&go traffic recently for like 45 minutes, never getting up past 8mph or maybe less. For the first 25-30 minutes, the battery was doing all the work and my mileage was amazing. Then the battery eventually drained pretty low, so my mileage went down to around 25mpg (the engine was doing all the work AND trying to recharge the battery). Guess I never got going fast enough for the regenerative braking to kick in. Just thought I'd share this experience, since I had been previously unaware that traffic could be so bad that fuel economy would suffer that much. Of course, the first 23-30 min. of 100mpg cancelled out the next 10 min. of horrible mileage.
What you report seems normal. Next time, if possible, turn off the air conditioner or run is as low as possible.
The "problem," if you can call it that, is that your instantaneous mpg takes into account how much gas you are burning and how fast you are travelling. It does not take into account how much you are charging or draining your battery. And since you cannot see how much charge is entering or leaving the battery, that figure is pretty much meaningless.
This is where a watt meter would come in handy. I use one in the house occasionally to monitor the drain my computers cause when they are doing things like burning DVDS. Maybe Coastal can add one to the brake/engine display, so we can see what the stereo and AC are using, and adjust as necessary when stuck in traffic...
