The Freakonomics of Human Fuel Economy

With gas prices high, I’ve heard a lot of articles assert that biking gives infinite miles per gallon. While it is true that humans don’t use gas, it’s not true that they don’t use energy.

When one walks, runs or bikes, one burns energy that would otherwise go unburned. For walking (4 mph), running (10 mph), and biking (11.9 mph) a 155 lb person burns 281, 1126, and 422 calories per hour respectively (according to this site). We can compute the calories per dollar of cheap food sources, such as grains (741 calories/dollar) or peanuts (867 calories/dollar). Let’s assume one can average 800 calories per dollar (which assumes spending about $2.50 per day on food on a 2000 calorie diet), which is a pretty generous assumption.

Let’s compute the miles/dollar assuming 800 calories/dollar: walking gives 11.4 miles/dollar, running gives 7.1 miles/dollar, and biking gives 22.6 miles/dollar. Assuming a gallon of gas is worth 4 dollars, we can express miles per dollar as miles per gallon. This means walking, running and biking converts to 45 mpg, 28 mpg and 90 mpg respectively. Very few Americans spend as little as $2.50/day on food. In fact, $10/day is probably more realistic. Assuming instead 200 calories/dollar (10 dollars/day), we get something like 11 mpg, 7 mpg, 22 mpg for walk, run, and bike. The only way I can beat the economy of my Prius is to bike and fuel that bike ride with ultra-cheap food sources.

Don’t get me wrong, exercise is great. I run, walk and bike a lot. Additionally, most Americans are eating more calories per day than they need, and could possibly bike for transportation without increasing their calorie intake. But, it is not the case that humans are much more efficient than cars.

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5 Responses to The Freakonomics of Human Fuel Economy

  1. on2Wheels says:

    “It is not the case that humans are much more efficient than cars”

    Economy and efficiency are two different things. Efficiency is not a measure of Dollars it cost to fuel, but how much energy it takes to fuel.

    A gallon of gas is about 31,000 Calories

    Biking at 12 mph = 240 Cal/hour
    Driving 30mpg car at 60 mph = 2 gal/hour or 62,000 Cal/hour
    or – at 12 mph = .4 gal/hour or 12,400 Cal/hour

    If you want to look at the “Economy” of riding a bike versus driving a car you need to look at the cost of the car itself and the environmental costs along with a host of other things.

  2. Marcus Twain says:

    Who runs at 10mph!? Also, most people walk at 3-3.5mph.

    • boykin says:

      10 mph is 6 min/mile. I can sustain that for maybe 10-13 miles depending on the weather. Word class marathoners can sustain sub-5 min/mile for 26.2 miles.

  3. Heather says:

    $10/day is expensive.

    By eating a Paleo Diet one can cut down the cost of eating to $5/day and that’s eating steak and shrimp my friend.

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