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Induced traffic induces more support

140313004 Highway WideningInduced traffic has been a regular topic of this blog, most recently three months ago when I wrote about peak spreading, a first cousin to induced traffic.

But induced traffic, the well-founded theory that road capacity creates car trips regardless of population changes, bears regular revisiting because its implications are a key motivating force behind walkable urbanism and because it’s non-intuitive to many (including me at one time), requiring repetition for its lessons to be assimilated.

And when better to revisit induced traffic than when there’s good news to report?

We’ll start in Houston, Texas, where, as reported in CityLab, the mayor came out strongly with the argument that more traffic capacity doesn’t solve congestion and may make it worse.

In words I’ve taken from the CityLab article, he opposed a possible freeway widening by saying, “This example, and many others in Houston and around the state, have clearly demonstrated that the traditional strategy of adding capacity, especially single occupant vehicle capacity on the periphery of our urban areas, exacerbates urban congestion problems. These types of projects are not creating the kind of vibrant, economically strong cities that we all desire.

Even better, the mayor won his office with a platform that included support for all modes of transportation other than single-occupancy vehicles, showing that Texas voters are willing to grasp the flaws of conventional traffic planning.

But the mayor’s continued endorsement of the theory of induced traffic doesn’t mean that the battle is won in Texas.  On the same day as he stated his opposition, the Texas DOT expressed their intention to reduce congestion by continuing to add lanes, including a widening of the freeway to which the mayor was referring, a freeway that is already 26 lanes wide.

Moving to California, Caltrans has released a policy paper acknowledging the validity of induced traffic and the reality that more roads often don’t ease congestion.  Not surprisingly, the consensus of the planners hasn’t yet filtered down to the rank-and-file, with those who rely on continued freeway projects for salaries and eventual pensions continuing to doubt the induced traffic phenomenon.

Coming closer to the North Bay, a Silicon Valley mobility guru, acknowledging that we can’t build our way out of traffic congestion, convened a group of transportation experts to rate other methods of addressing congestion.  The top three were higher gas taxes, charges for single-occupancy vehicle commuting, and vehicle mileage taxes.  I’ve previously written about the first and last, while also supporting the discouragement of single-occupancy commuting.

Lastly, California recently issued long-anticipated draft rules requiring that environmental impacts of car travel be measured by incremental vehicle miles traveled rather than intersection level of service, a paradigm shift that implicitly acknowledges the reality of induced traffic and is a more reasonable measure of environmental impact in an era when climate change is the governing concern.

Despite the explicit direction of the legislature to make the change, the rules haven’t progressed quickly, with the entrenched road-building constituency pushing back.  Nor are they likely to proceed quickly from here, but issuance of the draft rules is still a milestone to be marked.

I won’t argue that we’ve reached a tipping point on induced traffic, but we’re moving in the right direction on fronts in Texas, Sacramento, and the Bay Area, all of which should be considered good news.

In my next post, I’ll return to a point that I made in passing a few posts back, about weighing the credibility of widespread municipal corruption versus a systemic shortcoming in the U.S. land-use model.  I’ll invoke a 14th century logician and Sherlock Holmes to make my point.

As always, your questions or comments will be appreciated.  Please comment below or email me.  And thanks for reading. – Dave Alden (

Written by Dave Alden

Dave Alden

Dave Alden is a Registered Civil Engineer. A University of California graduate, he has worked on energy and land-use projects in California, Oregon, and Washington. He was also the president of a minor league baseball team for two seasons. He lives on the west side of Petaluma with his wife and two dogs. The blog that he writes can be found at

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