There’s a Lot Riding on U.S. DOT’s Definition of “Congestion”

Congress has done its job, such as it is, and passed a transportation bill. Now it’s handed off the policymaking to U.S. DOT, which must issue a raft of rules, definitions, and guidance to accompany the new law, known as MAP-21.

The wrong way to measure travel performance: "Travel Time Index" awards a better score to Charlotte than Chicago, even though commutes in Chicago are shorter, because drivers in Charlotte spend a higher percentage of their time in free-flowing traffic. Graphic: ## for Cities##

According to sources with intimate knowledge of this process, much depends on how DOT decides to measure congestion. New performance measures for the Congestion Mitigation and Air Quality Improvement program (CMAQ) — and quite possibly for the entire national highway system (depending how they define “roadway performance”) — require a working definition of congestion.

If the agency follows the prevailing orthodoxy, states could be rewarded for wasteful highway spending. If it adopts better measurements, smarter investments and less wasteful spending will follow.

The CMAQ measures will also require a definition of “cost-effectiveness,” a related but somewhat separate can of worms.

U.S. DOT Should Include Distance Driven in Any Measure of Congestion

Performance measures in the MAP-21 law have been criticized for being toothless, since many of them don’t have consequences attached. However, there is still the possibility that state performance rankings could be made public. And a spotlight on state failures could be an effective way to encourage good decisions.

Streetsblog asked Joe Cortright for his advice to DOT officials struggling to define congestion. Cortright is an economist and senior policy advisor for CEOs for Cities. In 2010 the organization commissioned him to write Driven Apart, a critique of prevailing methods of measuring congestion. His words of wisdom for U.S. DOT: “Don’t make the mistake the Texas Transportation Institute makes.”

TTI’s Urban Mobility Report, released every year, invariably gives top honors to places that have overbuilt road capacity. The institute measures congestion only by looking at the degree to which traffic slows down people’s commutes. The problem with that, Cortright says, is that “you end up rewarding places that encourage people to drive longer and longer distances, and then you look at those long distances that they’re traveling, and say because they’re moving at a relatively higher speed much of the time that they’re driving, that the system is somehow performing better.”

Over the past few years, U.S. DOT has been very deliberately working hand-in-glove with HUD and the EPA to treat transportation and land use as one cohesive system. It only makes sense that the agency use the same ethic in measuring roadway performance and congestion. By doing so, DOT would have to acknowledge that a long commute along miles and miles of free-flowing highways is no bargain compared to a short commute in dense traffic, not to mention an even shorter commute on transit.

Clark Williams-Derry, research director for the sustainability-focused Sightline Institute, suggests that congestion may simply be the wrong thing to measure.Focusing on congestion is like, in a basketball game, focusing only on the number of assists you get,” Williams-Derry said. “It’s an interesting fact, but it doesn’t tell you the final score.”

But people treat this one piece of the picture as if it’s “the whole story,” he says. Why not measure how long it takes to get from place to place? Or how much it costs? After all, a major argument against congestion – and the reason that congestion reduction is elevated to a national priority – is that time spent stuck in traffic is lost productivity, which adds up at a national level. But the TTI method actually masks how projects affect total travel time, and wouldn’t help measure productivity gains or losses.

The upshot is that following the same methods as TTI’s Urban Mobility Report to set performance goals under MAP-21 would be a huge mistake. “It would focus resources on projects that are sprawl-oriented, that encourage decentralized development,” Cortright said. “You can raise your performance on that measure most by having people drive more, as long as they’re driving faster.”

Cortright recommends that DOT put more emphasis on vehicle miles traveled than travel speed, and notes that this is especially important when it comes to measuring the cost-effectiveness of projects that are supposed to mitigate congestion and improve air quality. That’s another tricky definition DOT is going to have to figure out.

It’s Not Cost-Effective For U.S. DOT to Encourage Projects That Induce Driving

When DOT decides how to judge the cost-effectiveness of a CMAQ project, they can either focus on the CM (Congestion Mitigation) or the AQ (Air Quality), but those aren’t the same thing. “It’s unambiguous that if people drive fewer miles there’s going to be less pollution,” Cortright said. “A lot of the quote-unquote ‘congestion reduction’ projects essentially encourage more VMT.”

Widening roads induces more people to drive, which makes it a poor method to address congestion. Source: Todd Litman, the Victoria Transport Policy Institute

“There’s this pervasive mythology that our pollution problems are chiefly caused by people having to idle in traffic,” he continued. “There’s no evidence for that, and the evidence there is suggests that if you reduce congestion, people actually drive further, and that more than offsets the benefits of less idling.”

In addition, Williams-Derry pointed out that not all congestion is stop-and-go traffic. Congestion that consists merely of slower but smoothly flowing traffic actually improves air quality, since cars work more efficiently at slower speeds. That’s what makes CMAQ a tricky program to judge, since its two goals are sometimes at odds with each other.

If DOT is going to measure cost-effectiveness, Cortright and William-Derry say, it needs to think like a business. Starbucks would never build a second café next door so that it could move the line faster at 9:00 a.m. and then have it sit empty the rest of the day. Building more roadway capacity to handle peak-of-the-peak traffic makes just as little sense.

Cost-effectiveness also can’t be measured without examining what are known as “externalities” — the costs of driving that are passed on to the public. “The existing gasoline tax doesn’t even cover the maintenance on the highway system that we have now,” Cortright said. “It doesn’t reflect the economic losses to crashes, it doesn’t reflect the economic externalities associated with the environmental effects of burning all this gasoline and putting carbon in the atmosphere, and it doesn’t reflect the foreign policy and military costs of being so dependent on foreign oil.”

“If I were U.S. DOT, I’d try to add in, in figuring cost-effectiveness, the cost of all those other subsidies to automobiles,” he added.

There are still people inside and outside DOT – including some of the authors of MAP-21 inside the halls of Congress – for whom the only cost-effective transportation solution is to expand roads so cars can move faster. Not only would this do nothing to solve the problem of congestion, it would actually exacerbate the air pollution that the CMAQ program is designed to address. By being thoughtful about how to define success in the CMAQ program specifically, and roadway performance generally, U.S. DOT can have a tremendous and lasting impact on whether our transportation system is sustainable and sensible – or whether it drives us off a cliff.

13 thoughts on There’s a Lot Riding on U.S. DOT’s Definition of “Congestion”

  1. Excellent article, but I have one quibble.  You say, “cars work more efficiently at slower speeds.”  It’s not quite so simple.  Most cars peak in fuel efficiency around 40mph, and efficiency doesn’t get truly bad again until you start going quite fast.  Unfettered freeway traffic is quite efficient in terms of mpg as long as people don’t speed.  Congested stop-and-go traffic is terrible for efficiency, especially the way your average driver handles it.

    But to your point, unfettered freeways encourage more people to drive, and to drive longer distances.  This induced demand causes more pollution in the long-run.  And eventually all those new drivers re-create the congestion problem anyway. 

  2. Does anyone ever measure congestion reduction with the index? I thought that the headline measure of congestion-saving treatments (both highways and transit), at least the ones used by the TTI and the HSR project cost-benefit analyses, use total congestion cost, which is not the same thing.

  3. As usual, there is no consideration of the needs of freight movement here — it as if goods just magically appear on store shelves.  Congestion is congestion.  Redefining it to mean what the bicycle community wants it to mean will not pass the smell test.  Congress will have oversight over DOT’s decisions and they will haul the next Secretary in over what you’re proposing.

  4. This should be a non-contraversy: the standard measure of congestion is delay, measured in people hours. People hours times cost of time equals total cost of delay. This is basic transportation engineering. All the alternate measures cited in the article are problematic and would create distorted outcomes. Any congested freeway should be managed to maximize flow and minimize delay. Congestion pricing is the way to do this. You could literally burn the revenues and we’d still be better off than with traffic. Congestion is the second biggest economic drag on the us economy after chronic lifestyle diseases. The n

  5. Part of what’s missing is the linkage with land use. A well-designed transportation network disperses traffic and allows for multiple modes. Too many locales are single-use dominated and that virtually begs for auto-dominated transport.

  6. I enjoy this blog and particularly this article, but I would appreciate some additional context.  What variety of congestion metrics (e.g. shortest commute time vs shortest traffic jam time) do the 50 US States use?  …. ah I think the Driven Apart reference may provide more details, but is it only focused on cities, or also categorized by departments of transportation, where there may be more variety?

  7. Do you have guidance on the best ways the public can contact the US DOT to encourage them to adopt measures that reduce congestion and improve air quality (and encourage better and more balanced road design generally)?

  8. Charles: here’s your mistake; any time spent driving is really a “Delay”, but you haven’t counted it as such

    The standard measure should simply be commute time.  Shorter commute time == better.  If your roads don’t flow freely, but 90% of the people are walking to work 5 minutes away, you have low congestion.

  9. If you’re interested in freight, you want to look at time taken for typical freight to get to its destination.

    “Delay” is irrelevant.  You want to know how long it takes to get there.  Being closer to the source of the freight is better than having a faster road or railroad to get the freight there.

  10. Transportation is generally a means to an end, not an end in and of itself, e.g., a derived need. Therefore one wants to minimize total travel time, not just delay. As Clark Williams-Derry says in the article, delay is just part of the picture. Congestion and delay are important measures, but they aren’t the ultimate outcome measure. They are just part of the picture.

  11. Transportation is generally a means to an end, not an end in and of
    itself, e.g., a derived need. Congestion or delay is an important piece of the picture, and should be measured, but ACCESSIBILITY, e.g., the ability to reach goods, services, jobs, and other destinations, is a better outcome measure. While there are many ways to measure it, and many types of destinations, a good metric may be the percentage of jobs in a region reachable within a set threshold, averaged over the population (e.g., percentage of jobs that the average resident of the metropolitan region can reach within a 30 minute commute). It doesn’t then matter if the job is 20 miles away at an average speed of 45 miles an hour, or within a 5 minute walk (or a full time telecommuting job). It captures effects of land use, transportation networks, multiple modes, etc. The use of percentage of jobs means that the transportation infrastructure isn’t held accountable for a city with few jobs due to other reasons.

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