Data from: A century of sprawl in the United States

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.城市街道网络是城市最为持久的空间特征之一。一经规划落成，街道格局便会在未来数十年间主导城市形态与蔓延水平。本研究提供了1920年至2012年美国基于街道网络连通性测算的城市蔓延高分辨率时间序列数据集。城市蔓延早在私家车普及占据主导地位之前便已萌芽，并持续增长至20世纪90年代中期。但在过去二十年间，新建街道的连通性与网格状特征均得到显著提升；美国街道网络蔓延程度的峰值出现在约1994年。以连通性指标之一——交叉口平均节点度——测算，1994年至2012年间城市蔓延程度下降了约9%。本研究分析了此类变化的空间异质性，并证实了城市蔓延的持续性：即便街道网络持续扩张，原本采用低连通性街道网络规划建成的区域往往始终保持此类形态。本研究还发现了佐证性证据：地方政府政策会对城市蔓延产生影响，连通性提升最为显著的区域多为推行网格街道及新城市主义（New Urbanist）设计原则的地区。我们面向公众开放了县级版本的街道网络蔓延数据集，其时间跨度近百年。