A Novel (But Still Wrong) Argument for Widening a Freeway


Strong Towns member Joe Cortright runs the think tank and blog City Observatory. In this post, which is consolidated from two recent City Observatory posts and republished here with permission, Cortright digs into the “shifting rationale” for widening a stretch of freeway in Oregon.


The Oregon Department of Transportation is proposing to widen a mile-long stretch of Interstate 5 through Portland, at a cost estimated to approach $500 million. ODOT is offering up a shifting array of rationales for the project. While they conceded that the project won’t reduce the regular daily traffic jams due to induced demand, they argue that it will relieve congestion due by reducing crashes. The theory is that a wider road will have fewer crashes.

Even Agency Experts Agree Road Widening is Futile to Fix Daily Congestion

The project’s advocates have acknowledged that widening I-5 will do nothing to reduce the daily backups on I-5 that are associated with the heavy flows of commuter traffic.

Time and again, cities around the US and around the world have widened freeways with the avowed purpose of reducing congestion. And its never worked. One need look no further that the current U.S. record holder for widest freeway, Houston’s 23-lane Katy Freeway.  It was most recently expanded in 2010 at a cost of $2.8 billion to reduce congestion. It was even touted by road-building advocates as a poster child for freeway widening projects. But, as we’ve reported at City Observatory, less than three years after it opened, peak hour travel times on the Katy Freeway were 30 to 55 percent longer than they had been before the freeway was widened. The added capacity was swamped by induced demand, and congestion–and pollution and sprawl–were worse than ever.

This phenomenon is now so well-documented that it is referred to in the published journals of economics as “The Fundamental Law of Road Congestion.” Adding more un-priced highway capacity in urban settings only generates more traffic and does nothing to lower congestion levels.

Even the staff of the two agencies most responsible for the project concede that this is the case. Mauricio LeClerc is a principal transportation expert for the Portland Bureau of Transportation. Here’s his testimony to the Portland Planning and Sustainability Commission (emphasis ours).

When we did the analysis, the congestion benefit is on the elimination of crashes—non-recurring congestion. The congestion benefit of just adding more lanes was very limited.

This point was also confirmed by Travis Brouwer, a spokesman for the Oregon Department of Transportation, in response to questions posed by Jeff Mapes of Oregon Public Broadcasting.

Jeff Mapes:  It’s interesting, ODOT’s arguments—that’s the Oregon Department of Transportation—you know they’ve shifted a bit since the battleground has shifted now from the State Legislature to the City of Portland.  And they’re emphasizing now more the safety concerns—there are a lot of crashes there—but frankly the large majority of them are fender benders and that sort of thing, and secondly, but basically, they are saying if you take care of a lot of those fender benders, its; going to reduce a lot of delays that frequently happen there.

Here’s Travis Brouwer, he’s the assistant director of ODOT. He makes sort of their subtle case for the project, I guess:

Travis Brouwer: We fully admit that this is not going to eliminate congestion at the Rose Quarter, But, we do expect it will make traffic a lot better.

A Novel Argument: “Non-Recurring” Congestion

Instead, they’ve build the case for this project on its ability to reduce what they call “non-recurring” congestion–the delays associated with back ups due to crashes.

For traffic engineers, congestion comes in two flavors: ”recurring” and “non-recurring”.  “Recurring” congestion is the predictable daily (usually twice daily) slowing on a roadway that’s associated with the heavy demand from regular flows of commuters. “Non-recurring” means unusual congestion, the kind that’s associated with crashes, construction slow-downs or bad weather. While the distinction is almost certainly irrelevant to those of us stuck in traffic, its an essential part of the justification for this $500 million project. Superficially, it’s a plausible theory, but is it true?

A Real-World Experiment

The best evidence of whether the ODOT theory is right is an actual experiment. What happens when you widen a stretch of urban freeway like this one. Do crashes actually decrease?

As luck would have it, we have a timely and close-by real world experiment to examine. In fact, this experiment is on the same roadway, in the same city, and involves exactly the same kind of improvements, designed to solve the same kind of problems. In 2009, the Oregon Department of Transportation spent $70 million widening a stretch of Interstate 5 between Lombard Street and North Victory Avenue. They added a third lane to one side of the freeway, and widened shoulders on both sides of the freeway. The ostensible purpose of the project was to alleviate congestion and reduce the fender benders that created non-recurring delay.

So if a wider freeway results in fewer crashes, we ought to see it in the data. Let’s take a look at ODOT’s crash data for this stretch of Interstate 5.  ODOT reports crashes on a roadway segment that runs from Lombard Street to the Oregon/Washington border; the project in question represents about half of this segment. Here are the ODOT data on the number of crashes in this roadway.

The data show that prior to the project, this stretch of roadway experienced about 1 crash per 1 million miles driven, with some fluctuation from year to year between 0.9 and 1.1 crashes. Perhaps unsurprisingly, during the project construction period, which included calendar year 2010, the crash rate went up. After the project was completed, the crash rate came down, but has averaged about 1.1 crashes per million miles traveled, perhaps about 10 percent higher than the pre-construction equilibrium.

The important point here is that widening this particular stretch of freeway didn’t do anything to reduce the actual number of crashes recorded. If anything, the crash rate went up.

That’s got a very important implication for the proposed $500 million Rose Quarter I-5 widening project. This real world experience shows that more lanes and wider shoulders—on this very same freeway, carrying many of the same vehicles—does nothing to reduce the real world crash rate.

What this means is that neither of the supposed traffic improvement rationales for the I-5 widening project are supported by any evidence. The well-known effect of induced demand means that regular daily congestion will continue, a fact that state and local agency experts concede. Their claim that a wider freeway will somehow reduce crashes isn’t borne out by the actual evidence from ODOT’s last experiment with widening I-5—on a segment of road that carries virtually the same traffic and had (until 2010) the same kind of bottleneck. Instead, widening the freeway increased crashes. Because it will reduce neither recurring nor non-recurring sources of congestion, and may actually make them both worse, it makes no sense to spend half a billion dollars on this project if the objective is to reduce congestion.