What’s harder to figure out is just why driving and economic growth are playing this unchained melody. Via email to CityLab, Sundquist and McCahill point to a number of “big factors” that might have weakened the traditional connection. These include the rise of walkable places, where economic growth thrives precisely because there’s less driving; stagnant wages, which leads to less disposable income to buy a car or take a taxi; declining car use among Boomers and new travel preferences among Millennials; and marginal changes in commuting habits related to transit use or working from home.

Might we add one more to the list: the maturity of the American road network.