As cities grow and traffic increases, road capacity investments offer diminishing returns and even make traffic worse, according to a recent international study. Looking at 24 cities across the globe, researchers found that for every one-percent increase in road capacity, average traffic speeds drop 0.014 percent. Public transportation doesn’t suffer the same consequences.
Induced demand. It’s a concept that used to be popular only among the wonkiest transportation experts, and now gets covered by outlets ranging from the Washington Post to the Wall Street Journal. Governing calls it “the almost universally accepted concept” that almost no one understands, while Strong Towns calls ignorance of the concept “professional malpractice.” With new tools and a better understanding emerging, some transportation agencies are now beginning to wrestle with the implications.