Escaping Traffic Congestion

By Dom Nozzi

Many motorists inevitably engage in behavior that subverts our best efforts to reduce traffic congestion. “Induced traffic,” as Todd Litman points out, consists of three changes that motorists make when, for example, a road is modified by widening it: (1)  New car trips that occur as a result of road modifications that seek to reduce congestion, such as road widening. They are trips that would not have occurred had we not made the road modification; (2) Longer-distance car trips. These longer trips are caused, in one example, from a road change that speeds up car traffic (a longer trip can be made in the same period of time that a shorter trip was previously made); (3) Shifting from transit, bicycling or walking to car travel. “Generated traffic” occurs when a road modification such as a widening leads some motorists to shift to the newly-widened road, or shift to rush hour travel from non-rush hour travel (some motorists had previously avoided driving at rush hour due to congestion). Anthony Downs calls the above changes the “triple convergence,” which is the inevitable result of road widening. When a road is widened, three things inevitably happen: First, some motorists who were driving another route due to prior congestion converge back on the newly widened road. Second, some motorists who were avoiding rush hour driving converge back on rush hour driving. Third, some motorists who were using transit, were bicycling, or were walking converge back on car travel. One thing that the triple convergence informs us of is that motorist behavior works in reverse to self-regulate congestion (so that at a certain point, many motorists reach a tolerance level and opt to do something else). The triple convergence, therefore, works in reverse to self-regulate congestion. But only if we don’t undercut this self-regulation by, for example, widening a road. Or “timing traffic signals.” Or adding turn lanes. For example, self-regulation occurs because many travelers opt not to travel certain routes, opt not to travel at rush hour, or opt not to drive a car if a route is congested. If the route is less congested (widening or successfully encouraging some motorists to use transit or a bicycle, for example), those discouraged travelers “converge” back on the now less congested route. They also converge back on rush hour driving. Finally, some converge back on car travel. The road congests again. And rather quickly. Unless the community is losing population. Another way of putting this is that in our world, there will pretty much always be a latent demand for more driving. Much of that demand is discouraged or diverted by congestion. Much of the discouragement goes away when the road is less congested. Roads are not like pipes carrying water. They are more like pipes carrying gas. Expand the pipe and the gas expands to fill the larger pipe. We cannot loosen our belts to avoid obesity. We cannot widen our way (or shift to non-car travel) out of congestion. Many believe that “easing traffic congestion” will reduce emissions. However, Jeff Kenworthy and Peter Newman convincingly showed about 20 years ago that congestion reduces emissions and gas consumption, despite what we’ve always believed (one of the great many benefits of urban congestion). Why? Because as implied above, congestion imposes what Ian Lockwood calls a “time tax.” And “low-value” car trips (driving across town to rent a video at rush hour on a major arterial, for example) decline. Again, the key is not to strive to reduce congestion. Congestion, after all, is a sign of city vitality. A healthy city cannot (nor should it) reduce congestion. A healthy city must provide alternatives to congestion: convenient bicycling/walking/transit, compact development, pricing roads/parking, etc. And all of these healthy alternatives are much more likely, politically, when there is a lot of congestion. It is no coincidence that those cities with the worst congestion have the best transit. Congestion, in cities, is our friend. When we make it our “enemy,” we unintentionally join forces with the sprawl, road, and car lobby, since the default solution for reducing congestion (the only one that works in the short run) is road widening. One reason that congestion in cities is our friend is that, as Michael Ronkin notes, the most essential and effective way to reduce excessive car dependence (and promote walking/bicycling/transit) is to inconvenience cars. The most feasible way to inconvenience cars is to “let it be” when it comes to congestion. To not bankrupt ourselves and destroy our communities by widening roads or parking lots to reduce traffic or parking congestion. Increasing the number of people bicycling or walking not only will not reduce congestion. Such claims that increasing bicycling or walking will reduce congestion also perpetuates the downwardly spiraling, counterproductive efforts to try to reduce congestion. Those seeking a better community must end their (unintended) alliance with the sprawl lobby. Doing that means letting go of efforts to promote “congestion reduction.” And embracing efforts to provide ways to avoid the (inevitable) congestion.   _________________________________________________ Visit my urban design website read more about what I have to say on those topics. You can also schedule me to give a speech in your community about transportation and congestion, land use development and sprawl, and improving quality of life. Visit: Or email me at: dom[AT] 50 Years Memoir CoverMy memoir can be purchased here: Paperback = Hardcover = My book, The Car is the Enemy of the City (WalkableStreets, 2010), can be purchased here: is the Enemy book cover My book, Road to Ruin, can be purchased here: My Adventures blog Run for Your Life! Dom’s Dangerous Opinions blog My Town & Transportation Planning website My Plan B blog My Facebook profile My YouTube video library My Picasa Photo library My Author spotlight


Filed under Bicycling, Urban Design, Walking

3 responses to “Escaping Traffic Congestion

  1. I know this if off topic but I’m looking into starting my own blog and was wondering what all is required to get setup? I’m assuming having a blog like yours would cost a pretty penny? I’m not very internet savvy so I’m not 100% positive. Any tips or advice would be greatly appreciated. Cheers

  2. Carry, Thanks for your comment. I highly recommend the service I’m using to create a blog. Go to They offer totally free blog sites. And as you can see from mine, they provide quite a bit of quality for a free site:

  3. This is a great simple summary of why congestion and traffic are not bad for cities. In the community I live in, traffic is always used as a rallying cry to stop development. I live within a short walk of downtown and rarely drive so even when there is congestion (and it really is limited in duration) it doesn’t bother me. I also find it ironic that the people that complain about traffic are doing so because they are in their cars, guess what, creating traffic. I never hear people that walk and bike around town complain about traffic.

    Same thing goes for parking. People talk about the ‘parking problem’ here. The only parking problem we have is that you might not be able to park on the street in front of your destination when you want. Or that the most popular parking lots (those at the center of town) are full. I can almost guarantee that you can find a parking space in one of two lots at any time of day or night. And the parking, as is all the parking here, is free! However, those two lots are a block or 2 further from the center of town.

    We need more mixed-use development including housing downtown so more people have the option of walking/biking and avoiding the limited congestion. Thanks for the post. Glad I found it.

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