A team of researchers from the University of Toronto, the Neptis Foundation and the London School of Economics have tracked the evolution of land use in the continental US over time to create a picture of patterns of urban sprawl.
Urban sprawl is widely regarded as an important environmental and social issues, with major implications for the road infrastructure, fuel consumption and emissions. Much of the debate to date, however, has been based on speculation, according to the authors.
The team created a grid of 8.7 billion 30-meter by 30-meter cells and used high-altitude photos 1976 and satellite images from 1992 (the most recent available) to create coverage for the entire US for those two time periods.
The new high-resolution data allow the authors to observe the amount of open space in the neighborhood of every house in every US city. Since development is more scattered when there is more open space around a house, the authors measured urban sprawl by calculating the average amount of open space in the neighborhood of a house in each city.
Among their findings:
Los Angeles is less scattered than recent development in Boston.
Miami, San Francisco and Los Angeles were the most compact major cities, with Miami being the most compact.
Pittsburgh and Atlanta are the most sprawling.
Changing the number or size of municipal governments in a metro area has no impact on whether or not urban development is scattered, but controlling access to groundwater does.
More recent residential development is not any more scattered than development was in 1976. Forty-two percent of land in the square kilometre surrounding the average residential development in 1976 was open space, compared with 43% in 1992.
They found that while a substantial amount of scattered residential development was built between 1976 and 1992, overall residential development did not become any more biased toward such sprawling areas.
The authors also investigated why some cities are more sprawling than others. They found that a city’s climate, topography and access to groundwater account for 25% of the nationwide variation. When the climate is temperate, people spread out to have more space to enjoy the weather.
Hilly places see more scattered development as people avoid the costs of building on hillsides—but mountains act as a barrier and lead to more compact development. Places with easy access to groundwater see more scattered development, since people can supply remote houses with water by drilling inexpensive wells rather than paying for water lines.
The presence of aquifers is particularly important, and that seems to me to have policy implications. It looks as if controlling access to groundwater is an important way to control whether development spreads or not.—Matthew Turner, University of Toronto
Roads, on the other hand, have no impact on the extent to which development is scattered, despite commonly held beliefs to the contrary.
We looked at a lot of measures of road density—miles of road per area, average distance to a road, distance to an interstate exit—and we could find no relation between those measures and the scatteredness of development.—Matthew Turner
One of the common complaints about urban sprawl is that as development spreads, municipal services such as roads, sewers, police and fire protection are more expensive. The authors suggest that this concern is well founded. Development in municipalities that receive larger subsidies from higher levels of government is, on average, more scattered.
People have been eager to rush to policy prescriptions without a very good understanding of the underlying phenomena. We wanted to try to put the policy discussion on sounder footing.—Matthew Turner
The researchers received funding from the Social Sciences and Humanities Council of Canada, the Centre de Recerca en Economia Internacional and the Centre de Referència d'Economica Analítica and support from the Canadian Institute for Advanced Research and the National Fellows Program at the Hoover Institution.
The team is publishing its findings in the May issue of The Quarterly Journal of Economics, in a paper entitled “Causes of Sprawl: A Portrait from Space.”
Maps from Causes of Sprawl