Urban Sprawl, Cars Hamper Cities’ Best Efforts on CO2

There’s no way to drive around it:  commuting to work behind the steering wheel emits carbon dioxide and contributes to climate change.

Dense cities are pretty good at keeping those tailpipe emissions low when measured on a per-person basis because many commuters often use trains and buses to get to work.  Less dense cities, on the other hand, see more people driving to work from distant suburbs, usually leading to more tailpipe emissions.

A Boston University study published Monday in the Proceedings of the National Academy of Sciences shows that a major push in cities like Denver to build dense housing, better transit systems and more bike lanes in their urban core doesn’t necessarily lead to lower per-capita CO2 emissions.  That’s because suburbs continue to sprawl and residents there still drive to work.

“For the past 25 years, urban planners have been guided by the results of analyses that show how per capita emissions vary with population density across different cities because time-series data for individual cities’ emissions simply were not available,” Ian Sue Wing, associate professor of earth and environment at Boston University and a study co-author said.

The study fills that gap and shows that cities like Denver or Salt Lake can’t quickly become like New York or San Francisco in terms of vehicle emissions per person, he said.

Expanding low-density cities often add population far from centers of shopping and employment, forcing people to commute long distances to work and shopping trips and increasing emissions in the process.

“By contrast, cities that are already dense appear to be adding population much closer to these destination, resulting in faster increases in density, less on-road travel and flat or declining emissions per capita,” Wing said.

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