How Induced Demand, Freeways and Traffic Engineers Shape Phoenix

By: Taz Loomans

According to Jeff Speck, co-author of Suburban Nation and author of Walkable City: How Downtown Can Save America One Step at a Time, building more roadways DOES NOT reduce congestion. This fact has to blow the minds of Phoenix traffic engineers because the entire premise of the way our city is built is essentially based on a wrong assumption that they work under. That assumption is that the wider our roads and the more freeways we build, the easier it will be to get around.

Let me explain.

Speck says that the one thing traffic engineers never account for when planning new roadways is something called induced demand. Induced demand happens because new and bigger roadways make it easier for cars to travel. Eventually, so many more people opt to drive because of the new road or wider road that they become just as congested as when the roadway was narrower or wasn’t there at all. He cites a metanalysis of traffic studies that says, “on average, a 10 percent increase in lane miles induces an immediate 4 percent increase in vehicle miles traveled, which climbs to 10 percent—the entire new capacity—in a few years.” This means that people drive more when they have more road to use.

He also cites the 1998 Surface Transportation Policy Project, which looked at 70 different metropolitan areas over 15 years, that concluded, “Metro areas that invested heavily in road capacity expansion fared no better in easing congestion than metro areas that did not. Trends in congestion show that areas that exhibited greater growth in lane capacity spent roughly $22 billion more on road construction than those that didn’t, yet ended up with slightly higher congestion costs per person, wasted fuel, and travel delay.”

So, if more lanes doesn’t mean less traffic, does it follow that fewer lanes don’t necessarily mean more traffic? Is induced demand reversible? Once cars are accustomed to a certain ease and flow of traffic due to the existing number of lanes, would congestion increase if a few of those lanes were taken away, say to put in some bike lanes? Or would the congestion caused actually lead to reduced demand?

Speck argues that the inconvenience of congestion causes people to drive less and often results in people taking alternative modes of transportation. To prove his point, he notes that many of the cities with the worse congestion also offer the best public transit systems, giving people a tempting option to get around without dealing with congestion. He says, “Of the ten cities ranked worst for traffic in the 2010 Urban Mobility Report, all but three—Houston, Dallas, and Atlanta—have excellent public transit and a vast collection of walkable neighborhoods. Indeed, these seven cities—Chicago, Washington, Los Angeles, San Francisco, Boston, Seattle, and New York—also appear in another list: Walk Score’s ten “Most Walkable Neighborhoods” in America.”

What does this all mean for Phoenix? This city is very dependable when it comes to building wide roads and freeways in order to “reduce congestion”. But this has been at the expense of walkability and bike-ability. For example, traffic engineers opted NOT to put in bike lanes on Central where the Light Rail runs through it, in fear of reducing traffic flow even further.

Sacrificing vehicle lanes is anathema to the City of Phoenix Streets and Transportation Department. The new federally-funded streetscape project on Roosevelt between Central and 1st Street is supposed to be a flagship project demonstrating walkability and bike-ability, yet it still has a middle turning lane to reduce congestion. This shows how even today, traffic engineers are very much operating under the assumption that more traffic lanes equal less congestion, contrary to what Speck has shown to be proven. What if traffic engineers eliminated that middle lane and gave a buffer to the bike lanes to truly make that stretch of road pedestrian and bicycle friendly? Would this increase congestion or would it encourage people to drive less, especially on that stretch of road?

The best example (or worst, depending on your perspective) of how Phoenix has opted for more traffic lanes at the cost of walkability and bike-ability are the reversible lanes on 7th Street and 7th avenue. In the morning and evening, when people are going to work and going home from work, the middle lane becomes a traffic lane. In essence, the sevens become mini-freeways, getting North-Phoenicians to and from work easily and conveniently in their vehicles. This mini-freeway situation is said to keep the 51 freeway from becoming too congested. Again, this system operates on the assumption that more traffic lanes equals less congestion, which is not a safe assumption as demonstrated by Speck. But the worst part of this questionable strategy to keep traffic flowing is that it kills walkability and bike-ability on the sevens, which are adjacent to neighborhoods and have lots of small businesses lining their banks. The residents of the neighborhoods and the small businesses suffer because traffic engineers are still using an old assumption that doesn’t even yield what they’re aiming for – less congestion.

One solution might be for traffic engineers to be a part of a larger team of experts, including urban designers, landscape architects, architects, artists, sociologists and bike and ped experts when making decisions about widening or narrowing roads. Currently, traffic engineers seem to wield entirely too much power, and this is bad news if their thinking is based on bad assumptions. It’s also bad news because traffic engineers look at things through the singular lens of mathematics. Quality of life rarely figures into their thinking. So why are they are their recommendations taken above anyone else’s when it comes to quality of life issues? At the end of the day, the width of our roads is not a traffic issue. It is a quality of life issue, one that shapes what our city ends up looking like and feeling like. And traffic engineers should be just one of many multi-disciplinary voices that shape our city.

Photo Credit: A new section of the Loop 303 in North Phoenix. Photo from the North Phoenix Blog.

4 Responses

  1. I agree, but one aspect not addressed here is the political climate in which changes to road design must be made. If roads are narrowed radically in favor of bike lanes or public transit that are perceived, correctly or incorrectly, as underutilized, then there’s a genuine risk of a political backlash against the city officials who have made the changes.

    Those risks are real. Just look at Toronto mayor Rob Ford’s efforts to remove bike lanes and former Troy MI mayor Janice Daniels’ resistance to a federally-funded transit center. Elsewhere, activists show up at city meetings spouting Agenda 21 conspiracy theories that make bike lanes and rail transit sound like an Al-Qaeda plot.

    Maybe it’s sort of like the “Kenny Rogers” special that Songbird Coffee runs on Fridays. Do you want to gamble on a big win right away, or settle for smaller, safer steps toward a long-term goal? I don’t know the answer to that question, but it’s one worth keeping in mind when discussing the pace of civic transformation. I do like your suggestion of putting traffic engineers on a multidisciplinary team. I’d include some non-expert local area residents as well — to ensure broad buy-in and some political cover.

  2. By the way, I never type my comments with the caps lock on, but they always show up in all capital letters. That might be worth looking into.

  3. Well, moments after I posted my comments, I read that Rob Ford has been removed from office, just as Janice Daniels was a few weeks ago.

  4. […] effect of this “traffic solution” actually increased traffic due to induced demand while creating […]

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