One of the things I've done in my quest to get the maximum out of a tank of gas is to forgo the drive-through window. In so doing, I began to wonder how much gasoline is burned in the United States idling at drive-through windows. I decided to try to figure it out - maybe outlawing drive-through windows (something a person with a libertarian bent such as myself would never advocate) would end our reliance on imported oil.
I've read that Enrico Fermi felt his students should be able to come up with an estimate for almost anything. The classic example is to estimate how many piano tuners there are in New York City. There's even a competition to come up with order of magnitude estimates ("Fermi Answers") to obscure questions. Though I've never entered any sort of formal competition of this nature, the idea fascinates me. Anyway, such skills helped me with my answer to the query mentioned above.
Though "google is my friend," I wasn't able to find every piece of data I needed in my fairly brief search. I couldn't find statistics on how many fast food drive-through window visits occur in the U.S. in a day (or a year). Using estimates based on how many drive-through windows I think there might be, how often the people I know use them, what I've seen at the restaurants, etc. I decided maybe 1.5 million such visits occur each day. I estimated that an average visit is four minutes, and an average car burns 0.25 gallons per hour at idle (mine burns 0.38). I subtracted a minute because that was my guess as to the idling equivalent of pulling into a parking space, stopping and then starting the car after going into the restaurant.
Using these figures, I estimate that 18,750 gallons of fuel are wasted in drive-through window visits per day in the U.S., or about 6.84 million gallons per year. I was able to find a very informative site from a consulting geoscientist. I learned that a barrel of oil produces 19.5 gallons of fuel, so 6.84 million gallons require 350,000 barrels of oil.
I also learned that we use 21.93 million barrels PER DAY of which 13.21 million barrels are imported. So we import 4.82 billion barrels of oil per year. Thus, elimination of all fast food drive-through window stops could eliminate maybe .007% (that is, 7 one-thousandths of 1%) of our oil imports.
Well, ya gotta start somewhere...