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Sustain to gain: July 2011 Archives

Since Newman's and Kenworthy's work in 1989, the role of urban density has been controversely discussed as a mean to reduce gasoline consumption. Newman and Kenworthy's results are very suggestive - see figure below: With higher urban density, fuel consumption goes down with 1/x. Numerous studies have confirmed the basic relationship in different settings. However, the causal relationship still remains illusive (note that transport economists have worked on this issue since the 1970ties, but communities use different language and communicaton between communities remains sparse).

A key criticsm affects not the general results but the proper role of control variables that may co-correlate with urban density (e.g. Mindali et al., 2004). Karathodorou, Graham, and Noland recently published a paper that looks more closely on how a number of variables - including urban density - influence fuel demand. They decompose fuel demand into car ownership, fuel efficiency, and distance traveled by car, and look how each of these factors is influenced by urban density. Fuel efficiency seems to be not significantly correlated with urban density, perhaps because stop-and-go efficiency loss of denser urban areas is compensated by smaller cars more suitable for parking in dense urban areas. However, car ownership and transport activity are both significantly correlated to urban density. Using the Millenium Cities Database for Sustainable Transport, the authors find that the elasticity of car ownership with respect to urban density is around 0.12. The elasticity of distance traveled with respect to urban density is around 0.23-0.24.

While these numbers still not reveal causal relationships, this refined analysis sharpens the intuition on the role of urban density. 

Major cities - per capita petrol use vs. popul...

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