What do we do about traffic congestion?

If you ask someone this question, their answer often has more to do with policy preferences than with what’s likely to solve congestion. People who support private vehicles will tell you we should expand roadways. Many public transportation supporters (including most urban planning students) will say that public transit is the solution. Public transportation is, by and large, better for cities than private vehicles for many reasons, but even that won’t solve congestion. Both expanding roadways and improved public transportation are subject to the economic principle of induced demand.

Induced demand happens when we expand the capacity of transportation systems. We make it faster and easier for people to get from one place to another. People then respond to that added capacity by using it more!

When we add a lane to a congested highway, traffic may ease in the short term. Soon enough, though, people who had avoided the road, choosing to travel at other times or using other routes or methods, return. Congestion is back to where it started – or worse. The same goes for public transit. If we add public transportation along the same route, some drivers may switch to transit and others will fill in on the road.