The Environmental Impact of Your Two-Wheeled Commute

An analysis of greenhouse gas emissions per passenger mile traveled shows the environmental benefits of cycling and walking. Source: ##http://www.pietzo.com/storage/downloads/Pietzo_LCAwhitepaper.pdf##MIT##

Slate’s Brian Palmer wrote in an article this week that he’s thinking of switching his commute “from four wheels to two” but he’s concerned about the environmental impact of bicycling: specifically, “about all the energy it takes to manufacture and ship a new bicycle.” He wants to know how many miles he would “bike the drive” before he’s gone “carbon neutral.”

He estimates the average carbon cost of the manufacture of a new bike at about 530 pounds of carbon dioxide equivalents, based on a research paper published last year by MIT scientist Shreya Dave [PDF]. But Palmer never asks about the carbon cost of his car. According to an analysis by The Guardian, manufacturing a new mid-size car produces more than 17 tons of CO2e — about 75 times what it cost to make that bike. A top-of-the-line Land Rover would pollute twice as much, or 150 times the carbon footprint of the bicycle.

Palmer discounts the argument that bicycle “fuel” also harms the environment, since cyclists burn more calories and need to eat more. “As the Pacific Institute has shown, you’d have to be eating an all-beef diet to offset the environmental benefits of walking or bicycling,” Palmer said. “Given a ‘typical U.S. diet,’ you would have to ride your bike instead of driving for around 400 miles to cover the bike’s initial carbon footprint.”

The food argument also assumes that if you didn’t bicycle, you wouldn’t do any exercise at all that would require more caloric intake. Do people who don’t exercise really eat less? And either way, is an exercise-free planet really a healthier planet?

Adding up carbon output from fuel, infrastructure, maintenance, manufacture, and operation, Shreya Dave’s research doesn’t even bother with the food-as-fuel argument and puts the bicycle’s fuel carbon footprint at zero per passenger mile, though it does consider a relatively high operational carbon footprint since “a conventional bicycle requires the operator to work harder and breathe more heavily.” The data also claims, shockingly, that the carbon output of the manufacture of a bicycle, per passenger mile, is twice that of a Boeing 737, and that the infrastructure required to run the bicycle is 50 percent greater.

Still, Dave says that building, paving, and maintaining roads for cars emits almost four times the greenhouse gases as doing the same for bike lanes — in those special places where dedicated bicycle facilities even exist. And of course, Palmer writes in Slate, “your bike isn’t exactly tearing up the asphalt.” Weighing in at less than one percent of the weight of a Prius, a bicycle just isn’t responsible for the kind of road maintenance that cars are.

  • Sometimes Slate is kinda ridiculous. Even if you were going to make that comparison, you’d have to add in energy spent driving to the gym and running the treadmill, either that or energy expended on a coronary bypass. I’d imagine that’s actually pretty huge.

  • Where does this idea come from that people who use bicycles for transportation eat more? I eat the equivalent three meals a day regardless of how much I ride my bicycle.

  • mikesonn

    All this “math” is just to make those still driving feel OK about their choice. See, they don’t have time for all that math and adding up calories, etc. So, they can just keep driving thinking that they are somehow “eating less” and not wasting CO2 on “building new bikes.”

  • Anonymous

    People that exercise regularly will generally live years longer than sedentary people. How much extra greenhouse gases will you generate in those extra years of life?

    The same argument has been made about why exercise is bad for health care. Fit will require years more health care than fat people, so they spend more total dollars in the long run.

    Of course these arguments are silly. Bloggers often write because they can, not because they have an interesting point to make.

  • Joe R.

    I found I ate the same whether I was cycling only 500 miles a year, or over 3000 miles like I did last year.  The difference is I dropped a good 10 pounds by doing more cycling.  Generally people eat a set amount regardless of activity level.  The key is to increase your activity level so you’re maintaining a healthy weight.

    As for people living longer requiring more health care, this is a bogus argument.  Generally, people who don’t take great care of themselves will require more years of intensive health care even if they die younger.  Medical intervention can generally keep people alive until 70-75 no matter how poor their lifestyle.  An obese, sedentary person might start needing medical help in their 30s or even 20s.  By the time they hit their 50s they’ll be needing bypasses, statin drugs, hypertension medication, and probably start having occasional hospitalizations of ever increasing duration.  By their 60s they’ll likely require assisted living for their last 5 to 10 years.

    A healthy, fit person on the other hand will remain active, probably only need vitamins, well into their 80s.  By their 90s they might be looking at some medical care, mostly fairly minor, to cope with their advanced age, but will still be mostly functional.  This fairly low level of care will probably continue until multiple organ failure near the end of life sets in (basically the natural end of life).  For most people who have lived a healthy lifestyle this will occur between 100 and 105.  A lucky few make it past 110.  When it happens, the end usually comes within weeks or months.  Not much medical care other than making the person comfortable can be done.  Over their longer life span the healthy person probably needed at best months of intensive health care or assisted living, compared to decades for the unhealthy person.  Longer life spans though will affect programs like Social Security.  As such, we might need to think about increasing the age for benefits substantially if the population becomes healthier.

  • The lymph system of the human body needs movement in order to function, ergo movement is essential to human life. To pretend that somehow human beings can live without movement and that any activity that requires “extra” movement means “extra” carbon footprint is insanity. The same argument would imply that we could just stop breathing, too.

    A full one third of Americans are obese. An additional third are overweight. To claim that any form of movement would cause them to eat “extra” calories representing “extra” carbon footprint when they have years worth of “extra” calories carried around on their person is deliberately specious. Actually, unless you are Michael Phelps training for the Olympics, exercise will help control appetite rather than increase it.

    It would be interesting to document the lifelong carbon footprint of a healthy person versus an overweight, diabetic person that takes into account years of life, footprint of medical care and pharmaceuticals ingested, and the fossil fuels required for transport. (Heavier people take more energy per mile to move their mass.) I would guess the carbon footprint of most pharmaceuticals is quite high.

    Given that a quarter of the average person’s carbon footprint is due to transportation, I would seriously doubt that someone who walked or bike half their miles and as a result was pretty spry until they keeled over at age 80 (and who hadn’t done a lot of extreme sports and so didn’t need lots of hip and knee replacements) would require more lifetime medical care than a chronically sick person who was in and out of doctors offices his/her whole life until an early death at sixty-five.

  • Anonymous

    Cyclists are less bored and therefore less likely to have more children, and that by far is the greatest component of long term carbon footprint.

    Okay, so I have no support for this claim, but it’s consistent with observation.

    I definitely eat more when I ride more, so for my personal calculus this is a factor. But I agree health care consumption expectation is an important environmental factor extending way beyond simple carbon accounting.

  • Prinzrob

    If people who bicycle eat more, it is probably just because they have more money to spend on food which would have otherwise gone toward auto-related expenses. I know that since I stopped driving I definitely started spending more on higher quality food, but I only eat more calories when I am on the occasional long distance, recreational ride. For my daily commute and errand rides I just eat as usual.

  • Prinzrob

    Also, if one is that concerned about the minuscule carbon footprint associated with building a new bicycle let me remind you that there are LOTS of very fine, used bikes out there, many of which are built of high quality materials which will last longer than a new, low cost bike.

  • Exercise as appetite suppressant:

    “While the expression ‘work up an appetite’ has made it into the
    vernacular, the reverse might be the truth. When overweight people did
    three months of regular aerobic workouts on either a treadmill or a
    bicycle, they ended up eating less. There may be something chemical about exercise that helps increase
    brain-derived neurotrophic factor — a blood protein known to curb
    appetite. The higher the BDNF, the fewer calories the people in the study consumed (and the more weight they lost).” ( http://www.oregonlive.com/health/index.ssf/2008/12/you_docs_exercise_is_best_appe.html )

    More on the study:
    http://www.sciencedaily.com/releases/2008/06/080616115855.htm

    It may very well be that this only holds true for people that are overweight, but again, that’s two thirds of our population.

  • icarus12

    What I get from that chart is that outside of rush hour commuting, only bicycling, walking, and taking the subway (BART on this chart) are good on carbon emissions.  Traveling in off-peak buses is not much better than traveling by private car, for example.  That jibes with my experience of watching nearly empty buses roaring by at night spewing tons of fumes into the air.

    This makes me wonder if we should be designing further San Francisco transit that relies primarily on bus lines.  Why not spend the considerable money to build an integrated subway and tram system with fewer stops and time-efficient ways of getting around the city?  That way we could have 24 hour service that was practical, swift, and more environmentally friendly.

  • Reduce FOG

    Thanks for the insight. 

    BB

  • Icarus,

    In San Francisco, a sizable percentage of the buses are entirely electric supplied by hydro-electric power, so the carbon emissions for those particular lines are nearly zero at all times of day.  The diesel buses run with 20% biodiesel.  This is why when you look at the Muni emissions data, Muni on average is far below that of any kind of private car and fairly comparable to BART.  Which is not to say San Francisco shouldn’t invest in more light rail, or even in extending BART westward down Geary. It’s just very expensive compared to buses, and, sadly, above ground light rail stubbornly seems to run more slowly than buses do for reasons that passeth all understanding.

  • Joe B

    I think they’ve got the on peak/off peak manufacturing costs for buses backwards. Buses are manufactured to cover peak demand: the addition of off-peak riders does not cause the manufacture of additional buses, but the addition of on-peak riders does. Also, the operating costs are a little misleading, because additional people making off-peak use of the bus actually reduces the GGE/PMT. (The buses are driving half-empty anyways, so taking up an empty seat costs nothing.)

  • Ryan Ruhle

    As a 20 mile per day cycling commuter, I beg to differ. The energy I need to travel that distance per day plus mountain riding on the weekends requires a lot more than a normal 2400 calorie per-day intake. I’m not saying it means that overweight people don’t just eat too much, and some light exercise won’t help them eat less, but ‘working up an appetite’ is definitely a real thing.

  • Ryan Ruhle

    20 miles per day to school and back, I WANT FOOD!

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