Wednesday, June 22, 2011

Green Transportation- The Thermodynamics of Bicycle Commuting

Jeanne McHale, Newsletter Volunteer

            Bicycling is an extremely efficient form of transportation.  A typical cyclist burns about 400 calories per hour, less than is required for swimming, jogging, or cross-country skiing.  Those calories must be replenished, or cyclists would literally vanish into the sunset.  In this column, I consider the energy cost of bicycle transportation as opposed to driving a personal vehicle.  You may find some of this data rather shocking, but please read on before you make out your shopping list.

             Food calories as a unit of energy are actually kilocalories (kcal). When converted to units of kilojoules (kJ), they must be multiplied by 4,184.  So the apple I just munched, nominally 80 calories, provided me with 335 kJ of energy.  But the apple didn’t grow in my yard, it had to be transported.  Agriculture accounts for a considerable portion of our fossil fuel consumption.  According to Barbara Kingsolver, author of “Animal, Vegetable, Miracle,” a typical food item travels 1,500 miles to reach your dinner plate, and the average American’s food consumption accounts for about 400 gallons of oil per year.  My husband and I rack up about 3,000 mile per year on our Toyota, which translates to about 100 gallons of gas per year.  Yikes, could we be burning more oil by eating then by driving?

            Let’s look at this more closely.  As often as I can, I commute to work on my bicycle, a 32 mile round trip.  This takes me about two and half hours, consuming about 1,000 food calories or 4,200 kJ. The same trip in my car would burn a gallon of gas, which provides about 125,000 kJ, based on the heat of combustion of isooctane. This is 30 times as much energy as that required to fuel the engine of my bike, which burns “fat” instead of “oil.”   Sounds better to bike, right? But according to Kingsolver, each food calorie consumed requires dozens or even hundreds of calories from fossil fuel to raise, market, and transport it.  So unless I make local food choices, replenishing those food calories spent cycling could actually increase rather than decrease my fossil fuel consumption!

            The solution to the problem is to cycle and eat locally.  The Co-op, the Growers Market, and the Moscow Farmer’s Market provide many tasty alternatives to petroleum-intensive food products.  Food tastes so much better when it’s been raised locally and even better after an appetite-stimulating bike ride.  See you on the trail.

Green Transportation is written by Jeanne McHale, who notes that her own efforts to grow food this Spring have required petroleum input in the form of polyethylene sheets to protect seedlings from frost.