On the face of it this seems like a stupid question. If you drag your butt out of a car and ride a kick scooter to work, you are most likely preventing the incremental use of fossil fuel to power your car. (Of course it’s possible that you drive an electric vehicle that is charged by a solar panel. If that’s your situation, then the analysis is not so obvious. But, I’m betting there aren’t too many readers in that category.)
Are kick scooters green transportation?
To make the analysis concrete, consider a 2 mile commute (3.33 km). The average car in the U.S. requires 0.10 gallons of gasoline to cover that distance. Because some energy is required to extract, process, and transport the fuel, that’s equivalent to about 0.12 gallons of fuel “at the well.”
(I’m going to focus on the use of fossil fuel as a proxy for environmental impact. That lumps together lots of nasty stuff like mining, extraction, transportation, combustion, air pollution, green house gas emissions, and so forth. This is not a bad assumption, in my opinion, and lets us do some apples-to-apples comparisons.)
Now consider the energy required to ride a kick scooter to work. What energy? If a fit and lean commuter rides a scooter instead of sitting in a car, he or she will have to do about 20 calories (actually kilocalories) of mechanical energy to propel the scooter, and that energy must ultimately come from food. That doesn’t seem like much, except that delivering 20 calories of energy requires eating about 91 calories; our bodies are only about 22 percent efficient at converting food to mechanical energy via our muscles. It gets worse. On average, a calorie of dietary energy in the U.S. requires 5.75 calories of fossil fuel energy to grow, raise, harvest, process, and deliver the food that contains that energy. So, 20 calories of mechanical work actually ends up requiring 523 calories worth of fossil fuel — the amount in about 0.0165 gallons (~¼ cup) of gasoline.
The good news is that even with all that inefficiency, you are more than seven times more energy efficient on your scooter than when driving your car.
But, wait. Not so fast. If a previously sedentary individual takes up human-powered commuting, then he or she will live longer. No kidding. (There is a clear and well-documented relationship between physical activity and lifespan.) For every year a former couch potato exercises, he or she lives on average an extra 11 days. Unfortunately a modern human uses a lot of energy just getting through the day. In fact, a U.S. adult uses about 334 GJ per year of life (that’s the energy in about 2500 gallons of gasoline). That’s the equivalent of a lot of driving.
If you are sedentary and take up human-powered transportation, you will most likely consume more energy due to your increased longevity than you’ll save from not driving. So, you may want to think of human-powered transportation more as a way to live a longer, healthier life, rather than as a way to save the planet. (Of course, if this causes a lot of environmental guilt, you can just stop wearing a seatbelt when you drive.)
Note: a much more detailed version of this analysis for bicycle commuting can be found in the article The Environmental Paradox of Bicycling by Karl T. Ulrich, which is available for free.