A century of sprawl in the United States

Significance Urban development patterns in the 20th century have been increasingly typified by urban sprawl, which exacerbates climate change, energy and material consumption, and public health challenges. We construct the first long-run, high-resolution time series of street-network sprawl in the United States. We find that even in the absence of a coordinated policy effort, new developments have already turned the corner toward less sprawl. Initial impacts on vehicle travel and greenhouse gas emissions will be modest given that the stock of streets changes slowly, but feedbacks are likely to mean that benefits compound in future years. Our publicly released data provide further opportunities for research on urban development and the social and environmental impacts of different urban forms. 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.