[B’ Spokes: There are some good points in this article. I know people that will drive a good distance to a cheaper grocery story, spend $3 in gas and save maybe $3 in groceries. This is in part the justification of "needing a car" and why support for bicycling is low, simply because people mistakenly think you need to bike the same distance you drive when really you can manage quite nicely without all that mileage. My second point is many do not use mass transit in Baltimore because of the crummy bus routes and all the transfers needed to get to places, well add a bike to that and you can bike to a good bus line, get close to your destination and bike the rest of the way. Not a lot of miles on the bike but one long car trip has been replaced by one shorter bike trip.]
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by Tanya Snyder, Streets Blog
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,
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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.
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Sometimes Destination Follows Mode Choice, Not the Other Way Around
Models assume that a person decides on their destination and then picks their mode of travel. But sometimes the mode choice influences the destination.
If I’m on foot, I’m often going to go to the organic grocery store four blocks away, but it’s expensive. If I have access to a car, I might decide to go to a supermarket that’s farther away, but cheaper, and stock up on essentials.
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How the Experts Do It
Brian Gregor is a transportation analyst at Oregon DOT. He was instrumental in developing GreenSTEP, a tool that lets ODOT estimate and forecast the effects of various policies on the amount of vehicle travel, the types of vehicles and fuels used, energy consumption, and the resulting GHG emissions. GreenSTEP was used as a model for FHWA’s Energy and Emissions Reduction Policy Analysis Tool (EERPAT).
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To measure carbon emissions averted, Gregor doesn’t just use fuel economy averages. He looks at schedules of average fleet MPG by model year, all the way out to the year Oregon’s greenhouse gas emission goals are aiming toward, accounting for the full variety of vehicle body type and power train. Also in the mix is each fuel, including electricity, with its particular carbon intensity.
His team also factors in, at the household level, the number of people of different ages, their incomes, the land use type (urban or rural), the density of neighborhood, whether it’s a mixed-use neighborhood, the existence of transit service, and other factors — and from there, they determine the household’s likelihood of owning a vehicle, how many vehicles, the likely ages of vehicles, and their likely VMT.
That’s how they estimate carbon emissions — first at the household level and then at the state level. Could they have just multiplied the number of cars registered in the state by average VMT by average fuel economy by pounds of CO2 per gallon? Sure. But they wouldn’t have gotten very good data.
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https://dc.streetsblog.org/2013/03/29/how-much-driving-is-avoided-when-someone-rides-a-bike/
Biking in Baltimore