Looking for something else, I came across a web page that makes this rather startling claim:
[W]alking actually uses more fossil energy than driving, if the calories burned from walking come from a typical American diet.
The crux of the claim is that the North American food system is so dependent on fossil fuels—for manufacturing fertilizer and pesticides, running farm machinery, transporting food from farm fields to stores and homes, and powering refrigerators and stoves—that based on the typical American diet, walking a mile actually uses more fossil fuel than driving a mile!
This struck me as counterintuitive, but not completely ridiculous. So I spent some time looking at the issues.
And as far as I can tell, the web page is mostly wrong: walking is more energy-efficient than driving.
However, they’re closer than I might have thought.
Some quick calculations: according to this University of Michigan Center for Sustainable Systems analysis (careful, it’s a big pdf) and this Earth Policy Institute update, the US food system consumes about 10.25 quadrillion BTUs in fossil fuels per year—which is the energy equivalent of about 3/4 of a gallon of gas for every American, each and every day. (Very little of that energy is actually gasoline, by the way.) Based on this estimate, the food system burns about 6-7 times as many calories of fossil fuel as are in the food supply itself.
In other words, we don’t just eat food; we also eat oil, coal, and natural gas.
Obviously, your mileage may vary. If you eat lots of grain-fed meat, in particular, you’re likely to consume more energy in your diet. Then again, there’s practically no diet that’s truly benign; there are just darker and lighter shades of gray.
As for walking: for a 150 pound person, walking a mile burns about 43 calories above and beyond what the body would burn just loafing around. (See, e.g., here for calories per minute per pound of body mass for walking; and see here for what you burn while watching the tube.) Doing the math—and accounting for the fact that about 3 food calories are wasted for every 7 that are actually consumed (see, e.g, fig. 10, p. 30 of this big ol’ pdf.)—I get that a person who walks a mile gets the eqivalent of about 75 mpg.
That is, if you lump together all the fossil fuels that go into growing, transporting, selling, storing, and cooking your food, the human body uses a little less fossil fuel, mile for mile, than a high-tech Honda Insight.
However, walking is arguably less efficient—in per-passenger terms, at least—than an Insight with someone riding shotgun. In fact, in one way of looking at things, walking a mile is about as fuel efficient as driving a 15 mpg SUV with all 5 seats filled. Go figure.
Still, if you’re weighing whether to walk to the store or drive, walking is clearly the environmental winner—and it’s healthier, to boot.
And more to the point, a neighborhood where you can do lots of your chores conveniently on foot is bound to be a fuel efficient place—not just because you can walk or bike (which is more efficient than driving), but also because, day to day, you don’t have to travel far to get to where you need to go.
And the real efficiency comes from arranging our lives so that we don’t have to travel so far every day. That’s where the rubber (or shoe leather) really meets the road.
Patrick B. McGrath
As someone who works in the world of transportation policy I can easily imagine regressive types touting these statistics as reasons why we shouldn’t bother to invest in green transportation modes like walking and biking. In these discussions we must remember to identify our off-kilter food production and delivery system as the problem, not sidewalks and bike lanes.
Clark Williams-Derry
Good point. Also, this sort of thing can fuel a sense of futility—as in, *nothing’s* all that great, so I might as well give up. That’s a mistake, too.What I’m realizing through this and other posts is that the brouhaha over buses vs. trains, cars vs. SUVs, even walking vs. driving is sort of beside the point—and that the *real* driver of transportation energy consumption is neighborhood design. Build right (densely, with interconnected streets, space for a variety of transportation options, homes mixed with stores and services) and your transportation system is pretty efficient—whether it’s bike, bus, light rail, walking, even car or (gasp) SUV. Build wrong, and it doesn’t really matter what the mode, the system overall will be pretty inefficient.
John Schneider
Just to add to the last entry, I think people who walk, bike or use transit generally travel shorter distances to work or to get things in their neighborhoods. So even if the math suggests that driving uses less energy, acutally more is used because the distances covered are so much greater.
sf
The average fossil fuel energy required to eat is supposed to be 10 kcal fossil fuel for one kcal food. However, I’m sure there are many foods that are way under the average. It would depend on the calories per weight shipped, the feasibility of shipping in bulk, whether it needs refrigeration, and the degree of processing and packaging. Distance shipped is also a factor, but might not be as significant if the food can be shipped by railroad. The 100 mile criterion may not be important if the production of the food product is otherwise energy efficient. Intuitively, I would think grains, nuts, beans, oils, beet sugar and flour would be a lot lower than most foods. Anyone done any research on this?
sf
You may be off by a factor of 10. 31,000 kcal per gallon of gasoline divided by 43 calories per mile is closer to 750 miles per gallon.
Clark Williams-Derry
John—Couldn’t agree moresf – Right, but 31,000 kcal per gallon of gas, divided by 43 food calories per walking mile, divided by ~10 fossil fuel calories per consumed food calorie yields ~75 mpg. On research on calories for diffent kinds of foods—there’s a nifty piece of research from Sweden on this. See: http://tinyurl.com/fzg7b Of course, it analyzes energy consumption for food available in Sweden, not the US or Canada. But it’s instructive nonetheless. (Email me if you want the study itself: clark (at) sightline.org.)
toddwburley
In this comparison, was the full cost in fuel of the car and all its part included? If we are going to be so thorough about walking, why not with the production and maintenance of automobiles and the cost of disposal. And let’s not forget the external costs associated with automobiles such as pollution and mortality, health care and roads.
Sebastian Helm
While this is an interesting comparison, it overstates the factor a bit. The Insight is actually not quite “in sight” yet – it’s many miles away, if you include indirect energy consumption for the car as well. The Insight runs 60 miles on a gallon (http://www.fueleconomy.gov/feg/compx2005f.jsp?year=2006=Honda=Insight=Findacar); a life cycle analysis ( http://www.ilea.org/lcas/macleanlave1998.html) takes away one quarter, leaving 45 mpg – which is 30 miles behind the average pedestrian.
MickFinn2001
I just visited the website that provided you with the ‘interesting’ factoid (I’m using the original definition of factoid here: an untruth spouted as fact) that walking (or cycling in the orginal) wastes more gas than driving a car the same distance. I quickly discovered the basis for the faulty logic leading to the bizarre conclusion: another twisted argument as to why someone should adopt a vegetarian lifestyle over an omnivore lifestyle (if they really cared about the planet – oy, the guilt!). What factor did your source totally ignore in making this ‘argument’: the opportunity cost of putting someone in a car (or bus) versus in shoes (or on a bicylce). Producing a car (or the bicycle, or the shoes), the road for it to travel upon, etc., etc., etc, etc., and the energy it takes to do so should also be factored into the proposed equation – and once you do that, you quickly find there is no basis for the original claim. Just another tortured and poorly assembled argument to justify one lifestyle as better than another – so thanks anyway, I’ll just eating a balanced diet that includes meat and I’ll keep on walking (or cycling, or using mass transit).
Dan
It would be interesting to consider discussing that living a healthy lifestyle that includes frequent increases in cardio rate may lower health costs (externality), and such costs could be factored into this discussion.
franz
Yes, consider healthy life style and as importantly, healthy planet, as well. The two are inextricably linked. To cite but one example consider the “conventional” cropping system of corn in the midwest: fossil fuel based technologies are linked to human unhealthy diets (e.g. high fructose corn syryp, obesity, heart disease, diabetes, and so on) and to planet unhealthy nitrogen polluted ground water and runnoff and to an oxygen depleted dead zone in the Gulf of Mexico. The ecological systems analysis to make such connections is never required for economic decision-making and seldom available. It must be made manditory. Otherwise, people grab the “factoid” that validates their pet bias to justify behavior. We basically have a system of decision-making governed by bias, not ecological analysis. The discipline of ecological systems analysis, it seems to me, must be required. One of the founders of the field, Jay Forester, has successfully introduced systems analysis to elementary schools. Those of us who wrestle with questions such as the energetics of walking demonstrate the need for this kind of thinking as the narrative line of a discussion like this one gradually extends its boundaries to include more and more of the necessary considerations.
RRGreen
Do you know if anyone has performed a similar analysis for a horse?
RRGreen
I just figured out that a horse carrying a 165 pound rider traveling 50 miles in 6 hours burns 18300 calories. Its feed is about 60% efficient so the horse would have to eat 30,500 calories to make up for the expenditure of energy which is pretty much one gallon of gasoline. So following your methodology would I be correct in stating that the horse gets 50 mpg of gasoline? It doesn’t take into account the fossil fuel calories per consumed food calorie factor and based on the original article I don’t think that would apply because the horse eats a purely vegetarian diet part of which at least where I live grows right under its feet.
Clark Williams-Derry
Interesting!!I think, using my “methodology” (if you can call it that—that may be elevating what I did above its station)…if the horse eats grass you’d only count the fossil fuel calories (if any) used to grow the grass—e.g., natural gas for fertilizer, and perhaps oil used for any maintenance (periodic mowing perhaps).The fossil fuel numbers for my back-of-the-envelope guesstimate represented only fossil fuel energy used in the human food system—including energy for fertilizer & other inputs, transportation, processing, cooking and refrigeration, etc. If a horse’s food doesn’t require any of that, I guess my methods don’t really have anything to say about a horseback rider’s mpg.
Celeste
One question occurred to me immediately – what about the calorie intake of the driver (and passengers for that matter)? Admittedly, the driver (and passengers) do not burn as many calories as the walker; however, they have likely consumed as many calories as the walker. Just based on my experience and observations (I don’t have any studies to reference), most people eat roughly the same amount of calories whether they are engaged in moderate amounts of physical activity (walking from place to place as part of their daily routine) or drive everywhere. It is interesting to calculate the mpg of walking (particularly because it reveals the massive fossil fuel consumption of our current agricultural system); however, if the walker and the driver do consume the same number of calories, they in effect cancel each other out and the fuel consumption of the vehicle is completely additive.
payton
Urgh, the original stat is exactly the kind of single-issue thinking that is NOT helpful. And yes, I’ve seen this stuff pop up in other environmental circles.Celeste’s point is accounted for by Clark, but in any case I still bet that your average driver is not yet a vegan locavore. I burn an additional 400 calories on days I bike to work (vs. take the train), which is a nice bonus but still not “eat whatever I want” levels of exertion.The real kicker, of course, is trip length. Todd Litman notes that, in effect, a single mile of “nonmotorized travel” (let’s say “active travel”) displaces, in effect, seven miles of driving. (What he found is that cities with marginally higher levels of active travel have much lower VMT, probably highly confounded by smarter development patterns.) Durning, in one of his Bicycle Neglect posts, notes that car trips are about three times longer than bicycle trips.The point of the matter is that a walking trip is usually much shorter than a car trip—and assuming the trips ultimately accomplish the same ends, then energy expended per mile isn’t a valid measure; rather, the measure should be energy expended per trip. It’s like the old “mobility vs. access” debate among transportation planners: the goal of the network shouldn’t be to move cars faster, it’s to get people where they’re going.
payton
Alas, this “tall tale” made its way onto the NY Times’ web site today, courtesy of the perpetually contrarian junk-science nut John Tierney. The commenters properly rip the argument, but it hardly matters: the talking point has been planted, and we’ll surely be hearing about this (just as we heard about Tierney’s false claims of recyclables being landfilled) from wingnuts for decades to come.