The State of the Streets

Relatively little is known about the spatial organization of streets and roads in the world’s cities, the differences that exist across cities, or the differences that have emerged within cities over time. We use evidence from the Atlas of Urban Expansion—2016 Edition to investigate these questions, focusing on measures of road capacity and road connectivity. We compare outcomes in cities’ 1990 – 2014 expansion areas against outcomes in cities’ pre-1990 areas to determine the direction of trends over time and whether the observed differences are statistically significant. The analysis is based on a 200-city sample that was carefully selected to represent the universe of 4,231 cities with populations of 100,000 or more in 2010. Road network measurements were taken using an intra-urban sampling framework based on a Halton sequence of quasi-random analysis sites. Information for network capacity and connectivity as well as complete maps of cities’ arterial roads were created by the manual digitization of high resolution satellite imagery. We conclude that the composition of road networks is changing over time as new networks have narrower streets, fewer 4-way intersections, and fewer arterial roads. We explore the implications of these changes and how they may be addressed.