Proof that compact cities lead to reduced car use

February 26, 2015

The more compact the city, the fewer the cars… right? A new study — Connection Between Built Environment and Travel Behavior, published in the Journal of the Transportation Research Board — aims to determine whether that commonly-held wisdom is true. “[T]he compact city concept has become a paradigm of sustainable urban development under the premise that mixed-use, high-density cities can significantly reduce automobile dependency and promote the use of alternative modes.” Yet this idea, the study’s authors point out, is dependent on a true relationship between travel behavior and the built environment.

airplane between buildings

As it turns out, the long-held belief that denser cities mean fewer vehicle miles traveled is absolutely, undeniably true. Image from Simon and His Camera.

Is there a correlation between the built environment and its residents’ travel patterns? First of all, what does a “built environment” entail? “The built environment includes all of the physical parts of where we live and work (e.g., homes, buildings, streets, open spaces, and infrastructure),” notes the CDC.  It’s long been taken for granted among New Urbanists and other smart growth proponents that living in urban hubs will cause city dwellers to opt, increasingly, for public transit and other modes of transportation instead of cars.

As the researchers put it, “As concepts such as smart growth, compact cities, and New Urbanism permeate the sustainability discourse, the validity of the argument that high-density, compact, mixed-use cities might reduce car use and promote the use of alternative modes hinges on the existence of a true causal mechanism between the built environment and travel behavior.”

To investigate the relationship between people’s travel choices and the environment in which they live and work, the study’s researchers, who hail from the Department of Urban Engineering at the Graduate School of Engineering of the University of Tokyo, relied on March 2013 online surveys of 600 individuals in Hiroshima, Japan.

They gathered information on respondents’ households (such as whether the individuals had children and/or seniors at home), income, car use, job location, where the respondents spent their childhood, and individual attitudes and preferences — such as whether they identified as a “car lover,” and whether they were “pro-transit.”

To determine the level of urbanization, the researchers identified population density, average area of housing per individual, ratio of households living in multifamily residences within the area, ratio of renter households within the area, and density of commercial facilities. There are 460 districts in Hiroshima, the area the researchers studied; this study analyzed 400 districts as a sample size.

The researchers evaluated the relationship between the built environment and survey respondents’ travel behavior, discovering that high levels of urbanization were related to not only fewer car trips, but also shorter traveled distances by car. Increased urbanization was also linked to higher non-car trips and longer total traveled distanced (outside of cars).

“Findings support a causal effect of the built environment on some dimensions of travel behavior, namely, trip frequency and travel distances for car and nonmotorized modes,” write the researchers. In other words, more urbanization does lead to a drop in car use. “These findings,” they explain, “support the arguments by advocates that compact cities are a way to reduce car dependency and promote travel by alternative modes.”

Learn more about this study and other transportation analyses online at the Transportation Research Board.

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Category: Transportation

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