Chart suggestions
 

Cost per day graph?

It might be nice to show cost or gallons consumed per day. It would really help demonstrate your tip about not driving at all to save gas. Conversely if you took a roadtrip and got great MPGs (all highway) the dollar per day analysis would show you'd actually spent more money as opposed to saving.

I know you've got other shtuff to take care of, but there's my two cents. (which buys less and less gas every day...)