century of sprawl in the United States

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-07, Vol.112 (27), p.8244-8249
• Main Authors: Barrington-Leigh, Christopher, Adam Millard-Ball
• Format: Article
• Language: English
• Subjects: American history; Cities; City ordinances; City Planning - legislation & jurisprudence; City Planning - statistics & numerical data; City Planning - trends; climate; Computer Simulation; data collection; Environment Design - legislation & jurisprudence; Environment Design - statistics & numerical data; Environment Design - trends; Forecasting; Geography; Government Regulation; Humans; Impact analysis; issues and policy; local government; Models, Theoretical; ownership; policy; road network; Roads & highways; Social Sciences; Time Factors; Time series; time series analysis; transportation; Transportation - statistics & numerical data; United States; Urban Renewal - legislation & jurisprudence; Urban Renewal - statistics & numerical data; Urban Renewal - trends; urban sprawl; Urbanization
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1504033112

The urban street network is one of the most permanent features of cities. Once laid down, the pattern of streets determines urban form and the level of sprawl for decades to come. We present a high-resolution time series of urban sprawl, as measured through street network connectivity, in the United States from 1920 to 2012. Sprawl started well before private car ownership was dominant and grew steadily until the mid-1990s. Over the last two decades, however, new streets have become significantly more connected and grid-like; the peak in street-network sprawl in the United States occurred in ∼1994. By one measure of connectivity, the mean nodal degree of intersections, sprawl fell by ∼9% between 1994 and 2012. We analyze spatial variation in these changes and demonstrate the persistence of sprawl. Places that were built with a low-connectivity street network tend to stay that way, even as the network expands. We also find suggestive evidence that local government policies impact sprawl, as the largest increases in connectivity have occurred in places with policies to promote gridded streets and similar New Urbanist design principles. We provide for public use a county-level version of our street-network sprawl dataset comprising a time series of nearly 100 y.