Buy Local vs. Shop Local

Buying local has become all the rage lately (see Tree Hugger, 100 Mile Diet,Grist, or Local Harvest). I think there are some good reasons to do it. I think you should buy local because it is fresher. I think you should buy local because it allows for crops to be farmed that are bred for taste rather than for longevity and therefore they taste better. I think you should buy local if having a relationship with a farmer is something that you want. But I am suspect whether you should do it for environmental reasons. You see lots of claims like the following:

Today, the ingredients for an average meal travel over 1,500 miles. As a result, a huge volume of oil is used to transport food that could be purchased locally. Buying locally decreases transportation and thus helps America to reduce its reliance upon foreign oil supplies.

So it made me curious, how much fuel does it really take to transport my food and how does it compare with the fuel that I use to drive to and from the store?

I first tried to determine how much fuel it took to move my food. In this report (.pdf), they take a look at how much food can be transported per gallon of fuel with 3 different types of trucks:

semitrailor = 6.1 mpg * 38,000 lbs of food = 231,800 lb mile/gallon
midsize truck = 8.5 mpg * 13,775 lbs of food = 117,000 lb mile/gallon
small truck = 17.2 mpg * 1,550 lbs of food = 26,600 lb mile/gallon

Although the semitrailor only gets 6.1 miles to the gallon, because it can carry 38,000 pounds of food, it is much more efficient in pound miles/gallon than a small truck that gets 17.2 miles to the gallon.

This report also says that the average distance food travels in the US is around 1,500 miles, and the average for locally grown food is 345 miles. I assume that the long distance food travels by semitrailor and the local food by small truck.

For each pound of "normal" food:
1,500 miles / 231,800 lbs mile/gallon = .0065 gallons per pound
For each pound of local food:
45 miles /26,600 lbs mile/gallon= .0017 gallons per pound

Buying local saves .0065-.0017= .0048 (or .005) gallons per pound.

I weighed my groceries this week and it came to 20lbs. I don't know what the average is for an American, but I bet it is somewhere around there. If I bought only local, each week I would save 20*.005=.1 gallons. For an entire year that take me to 5.2 gallons of gasoline. That is not nothing, but given the average American uses 450 gallons of gasoline a year, it doesn't seem like a whole lot to me. There seem like a lot of other ways that could save much more than that.

Then I wondered, how does the gas used to transport my food compare with that I use to drive to the store?

The "normal" food I buy took 20lbs*.0065 gallons per pound = .13 gallons to transport. My grocery store is 2.6 miles away, or 5.2 miles round trip. Lets assume my car gets 30 mpg, then it works out to 5.2/30mpg = .17 gallons. So it actually takes more gasoline for me to drive to and from the store than it does to transport it all 1,500 miles from the farmers to the store. Of course, if I was shopping for a family of four and getting 80lbs of food, then it would be .52 gallons to transport vs. .17 for the drive.

Then I wondered, it terms of saving fuel, how does buying local compare to cutting out a Trader Joes run, or a second run to the store a week, or buying on the internet and having it delivered?

For me, I would save .1 gallons a week buying local. My Trader Joes is 2.4 miles away or 4.8 round trip. That would use .16 gallons. So, I would be better off skipping TJs and just sticking to the closest grocery store even if that meant no local food. For the family of four, they would save .4 gallons buying local, so if TJs has the local food, it would be worth it. If on the other hand, they were running (and by running I mean driving a car) to 2 stores twice a week (lets say 20 miles round trip) and they could cut it down to 1 store once a week (5 miles) they would be saving .5 gallons, which is more than what they would save from the local food. I don't have numbers but I suspect that buying "normal" food via internet delivery (ala Webvan) would save more gasoline than driving to your local store and buying local, due to the efficiencies of delivery vans if you were buying 20 lbs of food.

So, then I wondered, if I could choose between a normal grocery store with "normal" food or local food at a farmers market, how much farther could I drive to the farmers market and still save gasoline in total?

Buying local saves me .1 gallon a week. At 30mpg, that goes 3 miles (for the round trip). I could only drive an extra 1.5 miles to a farmers market if I was trying to save gasoline (or 6 miles if I was getting food for 4). So much for the idea of driving cross town to the farmers market to help the earth.

My final "then I wondered" was: what if the food was shipped from China?

I found this webpage that took a look at how many ton miles you can transport per gallon with ocean barges (assuming no backhaul).

Size of ship	Net ton-miles	Net pound-miles
	per gallon	per gallon
30,000 dwt	574.8	1,148,000
50,000 dwt	701.9	1,404,000
70,000 dwt	835.1	1,670,000
100,000 dwt	1,043.4	2,086,000

So, lets call it 1,500,000 lbs miles/gallon (compared to 231,800 for the semitrailor or 26,600 for the small truck).

The 6,000 miles it takes to go from China would use 6,000/1,500,000 = .004 gallons/lb. This is actually less than the .065 that it took to transport 1,500 miles via semitrailor. So, assuming that there is limited use of semitrailor before or after being on the barge, it actually takes less fuel to ship from China than it does to ship inside the US. Of course if it was flown over (which you would have to do if it needed to be eaten fresh) then I think it would use much more fuel.

So my take away from the whole buy local thing is that it doesn't really save that much fuel. In most cases, it would be better to focus of shopping locally and infrequently (or walking to the store) than to buy local. But of course there are other reasons to buy local, like because those local blueberries are oh so scrumptious.