Why “Build More Roads” Can Get You More Traffic, Not Less

Screen shot 2015-03-17 at 11.02.56 AMThe dream: a congestion-free road

Have you been complaining about traffic this week? You’re not alone. We all want better options for getting there faster, cheaper, and with less stress. Maybe, if you are like a lot of other people, your first thought is that we should build more roads and more lanes. Maybe just a cross-town expressway will ease Austin’s traffic woes, the thinking goes.

If Austin were Detroit, we wouldn’t have congestion. Not only is Austin a popular, rapidly growing city (110 people move here each day, with their 70 cars), but most of those cars want to come downtown at the same time each day. When more and more people want to be in the same place at the same time, we end up with a rush hour traffic jam. And just building more roads can’t keep up.

A growing body of research shows us that we can’t build enough lanes to grasp that free-flowing traffic dream of yesteryear. Even our local Chamber of Commerce has found that if we built all the infrastructure we can afford, all that building still won’t be enough to ease traffic. Why?

Building our way out of congestion would come with an immense cost, requiring incredible amounts of time, money, and space. There is no political will to spend all the money, take all the land, and bulldoze all the buildings that would be required to build roadways big enough to meet current demand, much less to meet the growth that is coming.

But there is more: when we add a new lane, we get a short period of improved traffic. It looks like everything is working, and we breathe a sigh of relief. But as people make decisions every day about how to travel, that new capacity fills back up. This is called “induced demand,” and it’s all about human behavior. Wes Marshall explains how it happens: “First, existing road users might change the time of day when they travel; instead of leaving at 5 AM to beat traffic, the newly widened road entices them to leave for work with everyone else. Second, those traveling a different route might switch and drive along the newly widened option. Third, those previously using other modes such as transit, walking, bicycling, or even carpooling may now decide to drive or drive alone instead.”

For these reasons, transportation officials have begun taking more seriously less costly and more effective approaches that focus on helping people make different decisions about how to travel, and making those alternative options more attractive and practical. If each person can shift just a few trips each week away from driving alone during rush hour, those small changes add up to make a difference.

So next time you catch someone complaining about the six new lanes we need on I-35, think about what happens when those new lanes become gridlocked. What are you going to say?

image via Creative Commons


One Response to Why “Build More Roads” Can Get You More Traffic, Not Less

  1. Even the immediate effect of adding road capacity can be to increase average travel times. And removing lanes or roads sometimes decreases travel times. Check out Braess’s paradox.