Does buying local reduce fuel consumption?

Yesterday I was walking down Houston Street (here in New York it's pronounced "HOW stun") and saw a handwritten sign on butcher paper in the window at Whole Foods. "Buying local reduces fuel consumption."

It's one of those things that seems so obvious it's not worth stating. It has to be true, right?

I'm not sure it's so clear. Consider this scenario, which for some reason is on my mind this Thanksgiving week...

A mail order company ships a loaf of bread made in Ann Arbor 250 miles to Chicago. The recipient in Chicago could have driven three miles round trip to get local bread. Does the shipped bread use eighty times more fuel?

Maybe if it was driven there overnight by one person, hands sweaty on the wheel. But if it was delivered by UPS it went as part of a route combined with other packages. And before that, in Ann Arbor, it was delivered from a bakery to the distribution warehouse on a route. And later, within Chicago city limits, it was delivered by a courier on a route.

How much fuel does each route take? I don't have any hard data here, but we can make some reasonable assumptions and probably get pretty close. Let's look at one leg, Ann Arbor to Chicago. I'll guess a full truck carries about 2,500 boxes, which is a pretty fair assumption given what I know goes in our trucks out back. That means for this 250 mile trip each box only travels one tenth of a mile, fuel-wise. Let's say an 18 wheeler gets 5 mpg. That means the loaf used 1/50 of a gallon on its Ann Arbor to Chicago route.

Use the same logic for the other two routes and you can work out hundreds of ways a 250 mile bread actually travels less than two miles and consumes less fuel than a local loaf.

There are lots of good reasons to shop local. I'm not knocking it by any means. I've made the scenario deliberately simplistic. Change a few numbers and things can go a different way, of course. I just wanted to show the economics are not necessarily as cut and dry as some signs may make them out to be.