Does riding my bicycle to work have a lower carbon footprint than driving my car?

My daily commute by car is 15 minutes on the highway each way. I drive a reasonably efficient car, so I’m going to call that 1 gallon of gasoline.

The alternative is to ride my bicycle 19 miles each way.

How many additional calories will I need to consume to cover that distance? The trouble is, power is dominated by wind resistance, and varies with the square of wind speed, which makes the answer quite variable. On sites like CPTips, we can find equations and tables for this. I’m going to use my 20mph cruising speed (on the flat) and come up with 750 kCal per hour. Conveniently, 19 miles with a little hill takes a little more than an hour, so I will assume 750 kCal each way, or 1,500 kCal round trip.

How much oil is used in producing the food I will eat to power than ride? I’m still looking for appropriate sources, but I’m hearing numbers like 100 Billion gallons of oil is used annually in production, packaging, and delivery of US food. Assume 300 M people, consuming 2,500 kCal/day, 365 days / year, and you get 0.4 gallons of fuel used for 1,000 kCal of food.

The oil used to produce the food I will burn commuting to work is about 0.6 gallons, compared with 1 gallon to drive the same commute.

The metabolism of that food will add a little more carbon dioxide to the atmosphere too - but I suspect it will be negligible compared to the fuel costs.

Capital Costs

I really should take into account the carbon footprint of the fixed-cost of the car too - not just the marginal fuel consumption. Again, I need sources. Assuming the energy required to make, distribute, and maintain my rather typical car is about 2,000 gallons equivalent, and that car now has nearly 200,000 miles, conservatively, I need to add an additional 0.01 gallons per mile, or 0.3 gallons of fuel for my commute.

The equivalent for my bicycle is harder to determine, since while the bicycle is much smaller, it also won’t get used for nearly as many miles. For argument, lets assume 25% of it’s $2,000 price tag was energy - or say 200 gallons of oil, and it will last for 20,000 miles. Amazing - that comes to the same 0.01 gallons per mile, or about 0.4 gallons of oil just to own the bicycle for a 40 mile round-trip!

Laundry

If I drive to work, I’ll wear my work clothes in the car.

If I ride my bike, I’ll use at least one set of bike clothing per day, perhaps two on a hot day. That probably translates to a load of laundry once a week, or perhaps 0.02 gallons of fuel equivalent (in carbon footprint). [Need sources]

Health Benefits

But won’t I win much bigger with the health benefits of cycling instead of driving?

On the positive side, I’ll be leaner, with lower blood pressure and cholesterol and all the other benefits of regular exercise.

On the negative side, once every 18 months I would have an injury accident, if the stats are to be believed, and perhaps once every 10 years a serious accident. How many days of carbon emissions savings from bicycling are used up when the ambulance and firetruck rush to the scene, and in fixing my broken leg or worse? I have no idea how to quantify these impacts.

Musings

I am disturbed that cycling has a carbon footprint apparently so close to driving; if I drove a Prius, it would appear, first order, to be more carbon-efficient than cycling!

One key observation is that if I weren’t riding my bike to work, I’d probably be finding some other way to be active (and hopefully healthy?), so I might as well at least use the effort to save a car trip.  This is probably the best counter argument to the argument to drive…

References

200 kWh/year to run 392 laundry cycles per year ~= 500Wh per load or ____ carbon footprint.