Reid Ewing

Before Ewing, sprawl was discussed with adjectives. He turned it into a composite index — density, use mix, centrality and street network connectivity — and calculated it for every metropolitan area in the United States. That made it possible for the first time to correlate urban form with measurable outcomes: vehicle miles travelled, obesity, pollution and, very consistently, traffic fatalities.

His second contribution is the so-called D variables, formulated with Robert Cervero: density, diversity of uses, design of the network, destination accessibility and distance to transit. His 2010 meta-analysis, pooling more than two hundred studies, established how much each actually weighs. The conclusion annoyed everybody: each variable on its own has little effect, and only acting on several at once produces an appreciable change in behaviour. There are no shortcuts.

A professor of city and metropolitan planning at the University of Utah, where he directs the Metropolitan Research Center, Ewing previously worked in Florida drafting state growth management rules, and that experience shows in his insistence on producing figures a court or a council meeting can use.

Growing Cooler (2008), with Keith Bartholomew and others, quantified how much emissions urban planning can save compared with improving vehicles, and became a reference for American climate policy. Measuring Urban Design (2013) did the hardest thing: giving numerical value to qualities that seemed subjective, such as the visual permeability of a façade or the complexity of a street, and testing which are genuinely associated with walking more.