Planetizen - Urban Planning News, Jobs, and Education

Induced Demand Explained (or Why We Can't Build Our Way Out of Congestion)

In case you need an easy link to reference when encountering arguments in favor of widening roads and freeways as a solution for traffic, Adam Mann provides an accessible and clear explainer article that sums up the limitations of such strategies.
June 18, 2014, 12pm PDT | James Brasuell | @CasualBrasuell
Share Tweet LinkedIn Email Comments
Jeff Turner (JefferyTurner)

Adam Mann on why we can't build our way out of congestion: "The concept is called induced demand, which is economist-speak for when increasing the supply of something (like roads) makes people want that thing even more. Though some traffic engineers made note of this phenomenon at least as early as the 1960s, it is only in recent years that social scientists have collected enough data to show how this happens pretty much every time we build new roads." 

The article cites the research of Matthew Turner of the University of Toronto and Gilles Duranton of the University of Pennsylvania on the the fundamental law of road congestion, or, as Mann explains: "New roads will create new drivers, resulting in the intensity of traffic staying the same.

Mann explains how this counterintuitive reality can possibly be true: "As it turns out, we humans love moving around. And if you expand people’s ability to travel, they will do it more, living farther away from where they work and therefore being forced to drive into town. Making driving easier also means that people take more trips in the car than they otherwise would."

Mann also details two of what he considers to be more rational solutions for the problem, congestion pricing and the price of parking.

Full Story:
Published on Tuesday, June 17, 2014 in Wired
Share Tweet LinkedIn Email