Source: adapted from Newman, P. and J. Kenworthy (1999) Sustainability and Cities: Overcoming Automobile Dependence, New York: Island Press.
There is an intricate relationship between urban density and energy (fuel) consumption related to transportation. Regional divergences are observed, which are linked with demographic, economic, and societal characteristics. North American cities are among the most energy-intensive, while Asian cities are much less energy-intensive. Two main factors explain why transport-related energy consumption increase exponentially as urban density decreases:
- There is a shift from collective and non-motorized forms of transportation towards automobile use, implying a fast increase in energy use.
- The average commuting distance increases, implying a non-linear growth of energy consumption with return trips.
The strong association between density and car use indicates that modal preference, urban form, and density are closely related. While for Houston, dispersed developments and low densities leave little choice other than car usage, denser locations such as Paris and London have many more alternatives. The challenge of many cities wishing to address car dependency is to offer development plans that meet the mobility demands of their populations while increasing density.