Is riding to work green?
I got a folding bike last year, and a 2012 resolution has been to make it my default mode of intra-city transportation. I lived that dream today, which included errands in three different neighborhoods and saw me put in about 20 miles over five legs of riding.
There’s a lot of reasons to ride a bike in the city – it’s faster, it’s free, and it’s much more engaging than a subway ride or walk. But high on that list to me was always the green aspect – I’m burning no fossil fuels on the way. You can’t beat a bike for green-ness, right? Just as I was sizing myself up for a Citizen of the Year jacket, Winston Wolf had something NSFW to say about my smugness.
My whole argument started to fall apart as I sat down to eat post-rides and noticed that I was freaking hungry. These miles I rode, they required energy. Energy that needed to be replaced. It’s just that instead of the gas pump, I was filling up at the dinner table.
Here’s some back-of-the-napkin stuff:
I rode 20 miles on my bike. Because of gears, coasting, terrain, and individual body types, there’s no definitive answer of how much energy that takes up, but online estimates average 30-40 calories per mile*; I’ll go with 35 for this exercise. That means I burned 700 extra calories riding around today, which I’m replacing with some killer chicken with cashew nuts I made last night. But that’s not all the energy I’m using up, because for each calorie I consume, several more have been expended along the way – to produce, process, refrigerate, and transport the food from farm to table. The national average is about ten calories of energy expended per calorie consumed. There are a few other factors at play: on the one hand, getting produce straight from farmers means a lot less travel for my food, which suggests a lower number than 10 calories used/calories consumed (CU/CC); on the other, the ingredients I tend to use, like leafy green vegetables and meat, are less energy-efficient to produce than, say, corn, which suggests a higher number than 10 CU/CC. I’m going with ten. That means my bike riding cost the world about 7000 calories.
What if I had driven? A gallon of gas has about 31000 calories. There is also energy required to remove and refine, but this is much less than that of food: it’s about 1.5x the energy in the gasoline itself. That leaves us with 46,500 calories. And if I’m in a car that gets 20mpg in the city, that’s the final tally on fossil fuel usage: 46500 (car), 7000 (bike). Big environmental win for the biker.
Now, it’s easy to imagine a scenario where the car actually is the greener option. If the dude flying solo in the Chevy Impala gives way to four people rocking a Prius together, then biking is actually the less-efficient way to go:
PRIUS: 46,500 calories/gallon / 40mpg x 20 miles = 23,250 calories
BIKERS: 7,000 calories x 4 riders = 28,000 calories
Of course, this situation would rarely occur. And this whole analysis doesn’t take into account the energy required to build a car vs. building a bike, which would skew things further in favor of the cyclist. So we can assume that, in the world of green peoplemoving, bike beats car.
How about mass transit? There’s a couple of ways you could look at that one. You could look at all of the energy required to build your area’s mass transit system, and divide it by the total number of miles ridden by passengers, but this is unrealistic and, for the purposes of this argument, probably less accurate than the approach I’ll use here: since the subway and bus systems are up and quite operational already, and will do their thing whether I used them or not, then the marginal energy expenditure required to move me – that is, the amount of additional energy required to get this particular 162 lbs. of twisted steel and sex appeal on his merry way – is zero. The only energy expenditure we’d have to deal with is that associated with the walk to and from the subway stations. Assuming a total of 15 minutes’ walking, or 3/4 mile, per trip (75 calories expended walking, or 750 calories total replacement energy required) each trip, and using the five legs of my own bike journey:
MASS TRANSIT: 750 calories per trip x 5 trips = 3,750 calories
BIKERS: 7,000 calories
Subway beats bike.
*”Calories” are an annoying concept. A scientist will tell you that what we consider a calorie (the number printed on nutrition information labels) is actually 1000 calories (the amount of energy required to heat one gram of water one degree Celsius). And he’d be right. But come on, man! At some point along the way, some genius decided that 1000 calories would be one kilocalorie or “Calorie” (capital “C”), without considering for a moment that this might create some nomenclature problems. This may have been a Smart thing to do, but it was definitely not a smart thing to do. For the purposes of this article “calorie” means what we, the nonscientist consumers, think it means.