Urban myth busting: Congestion, idling, and carbon emissions``

By Joe Cortright, City Observatory

Increasing road capacity to reduce greenhouse gas emissions will backfire

Time for another episode of City Observatory’s Urban Myth Busters, which itself is an homage to the long-running Discovery Channel series “Mythbusters” that featured co-hosts Adam Savage and Jamie Hyneman using something called “science” to test whether commonly believed tropes were really true.
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Today’s claim comes from the world of transportation. As we all know, transportation is now the single largest source of greenhouse gas emissions. Here, when confronted with the need to do something to address climate change, the highway lobby likes to point out that cars emit carbon, and when they’re idling or driving in stop and go traffic, they may emit more carbon per mile than when they travel at a nice steady speed. And of course, they have a solution for that: spend more money expanding capacity so cars don’t have to slow down so much. That’ll be great for the environment, or so the argument goes.
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In place of the now retired duo of Adam and Jamie, we’ll turn this question over to Alex and Miguel–Alex Bigazzi and Miguel Figliozzi, two transportation researchers at Portland State University. Their research shows that savings in emissions from idling can be more than offset by increased driving prompted by lower levels of congestion. The underlying problem is our old friend, induced demand: when you reduce congestion, people drive more, and the “more driving” more than cancels out any savings from reduced idling.
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http://cityobservatory.org/urban-myth-busting_idling_carbon/