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The National Center for Sustainable Transportation will host a webinar later this month to discuss research that shows that building new and wider roads is at best a temporary fix for congestion. Most studies show that adding roadway capacity in congested areas ends up increasing the amount of travel over the entire network, negating any initial congestion relief.
The concept is called "induced travel." Transportation planners, including at Caltrans and the Southern California Association of Governments, have resisted the notion, which seems to fly in the face of the logical response to congestion: widen the road, giving travelers more room. But studies show that increasing roadway capacity by ten percent leads to between six and ten percent more overall travel--and that's on an entire network, not just the one expanded project.
New rules under the California Environmental Quality Act call for planners to measure this effect for many projects, and Caltrans is developing guidelines for how to do so. A 2013 law, S.B. 743, called for an end to using traffic congestion as a measure of the environmental impact of a project, since that took into account only the impact on driver delay, and left out other important impacts like safety and the number of new vehicle miles traveled (VMT) a project would likely produce.
It's also simpler to measure VMT than it is to estimate delay. Planners are more accustomed to the latter, however, so researchers working with the NCST have developed a web-based calculator to make it even easier.
The webinar, on May 23, will discuss the concepts underlying induced travel and summarize current research on the topic as well as talk about how measuring VMT more closely reflects environmental impacts from travel. Then it will introduce and discuss the new VMT calculator, with input several experts including Chris Ganson from the Governor's Office of Planning and Research.
