If Jane Doe rides her bike a mile to the post office and then back home, is it fair to assume she just avoided two miles of driving? And can we then assume that she prevented 2.2 pounds of carbon dioxide from being emitted?
That’s more or less the way most agencies calculate averted vehicle-miles traveled. One mile biked is one mile not driven.
That simple assumption masks enormous complexity, however. And with at least 33 states and hundreds of cities, towns, and counties having instituted climate action plans or emissions reduction targets, we’re going to need a better method of measuring the carbon that biking keeps out of the atmosphere.
It’s not too hard to figure out the carbon savings from reduced VMT. But looking at it the other way around — calculating the carbon-reduction benefits of increased biking — can be a challenge.
If bicycling is on the rise in your city — because of bike-share or better infrastructure, for example — what does that mean for your city’s carbon footprint? A mode shift metric that accurately captures this information could encourage municipalities to invest more in biking and walking as a carbon reduction strategy.
Not that biking always replaces driving. Some bicycle trips are primarily recreational and wouldn’t be made by any other mode. Or if someone shifts from bus commuting to bike commuting, then they’re obviously not taking a car off the highway (though the newly available space on the bus might then be filled by someone making the switch from driving to transit). Ten million U.S. households don’t have access to a car, according to the Brookings Institution, and regular cyclists are probably over-represented in that number. Shouldn’t it change the equation if a cyclists’ backup mode is transit or walking?
But there are also reasons to think that the 1:1 ratio is actually undercounting vehicle miles averted, and therefore underestimating the power of mode shift. Read more…