Barrington-Leigh Christopher, Millard-Ball Adam
Institute for Health and Social Policy and McGill School of Environment, McGill University, Montreal, QC, Canada H3A1A3;
Environmental Studies Department, University of California, Santa Cruz, CA 95064.
Proc Natl Acad Sci U S A. 2015 Jul 7;112(27):8244-9. doi: 10.1073/pnas.1504033112. Epub 2015 Jun 15.
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持久的特征之一。一旦建成，街道格局将决定未来几十年的城市形态和蔓延程度。我们展示了1920年至2012年美国通过街道网络连通性衡量的高分辨率城市蔓延时间序列。蔓延早在私家车拥有量占主导地位之前就已开始，并持续稳定增长直至20世纪90年代中期。然而，在过去二十年中，新街道的连通性显著提高且更具网格状；美国街道网络蔓延的峰值出现在约1994年。通过一种连通性度量方法，即交叉路口的平均节点度，蔓延在1994年至2012年间下降了约9%。我们分析了这些变化的空间差异，并证明了蔓延的持续性。即使街道网络在扩展，那些以低连通性街道网络建成的地方往往保持原状。我们还发现有暗示性的证据表明地方政府政策会影响蔓延，因为连通性增加最多的地方是那些推行网格状街道及类似新城市主义设计原则政策的地方。我们提供了一个县级版本的街道网络蔓延数据集供公众使用，该数据集包含近100年的时间序列。
