By Dom Nozzi
Traffic light synchronization seems like a common sensical, no-brainer “solution” to relatively cheaply reduce air emissions and gas consumption. It seems so obvious that even highly intelligent progressives and environmentalists (nearly all of them) STRONGLY support this tactic.
Michael Vandeman, in his article, “Traffic Light Synchronization — An Air Quality Benefit, or a Sop for Motorists?,” points out that many are misled when it comes to traffic light synchronization. “[W]hen a proposal sounds reasonable, and is at the same time extremely popular, scientific accuracy is often forgotten. In this case, none of the researchers [for synchronization] considered the possibility that making it easier to drive might cause people to drive farther and more often, cancelling the alleged benefits. They were apparently so eager to help their fellow motorists…that they neglected to apply strict scientific standards to this research.”
Those who trumpet the alleged benefits of synchronization fail to take into account about the “induced demand” that Vandeman rightly points out. That is, they forget that the amount of travel by car is higher or lower based on the ease of car travel and the cost of car travel. The easier and cheaper we make car travel (As Jevons Paradox shows us. See: http://en.wikipedia.org/wiki/Jevons_paradox), the further people will travel by car and the more frequently that car travel will occur. In other words, if gas costs $20/gallon, people will drive less. If streets are congested or traffic signals force one to engage in start-and-stop driving, people will drive less.
When people drive less, air pollution and gas consumption are reduced. Because traffic synchronization makes cars happier and thereby encourage more driving, air pollution and gas consumption are increased, not decreased (as most assume). Therefore, despite the overwhelming conventional wisdom, traffic synchronization does NOT reduce air emissions or gas consumption.
Vandeman agrees when he points out that it seems like common sense that synchronization is a good idea. “Everybody knows that a motor vehicle pollutes more in stop- and-go traffic than in smooth-flowing traffic. This fact has been used to justify expanding freeways, synchronizing traffic signals, and a multitude of other measures to speed up traffic.”
The big mistake, according to Vandeman, is to inappropriately generalize. “[I]t is not valid to generalize from a single vehicle on a single occasion to a whole street full of vehicles over a long period. Newman and Kenworthy demonstrated why congestion relief in the form of roadway expansion actually worsens emissions and fuel consumption: although an individual vehicle may benefit, that effect is far outweighed by the fact that making traffic flow freely encourages people to drive farther and more often and makes it much less likely that they will choose to travel via public transit, bicycling, etc. In other words, highway expansion doesn’t simply speed up individual vehicles, leaving the number of trips and VMT constant. If it did, it would be beneficial…Similarly, synchronizing traffic signals doesn’t just speed up existing trips. By making it easier for people to make long trips by automobile (while providing no benefit, or negative benefit, for bicycles and buses), could cause an increase in trips and VMT that would outweigh the alleged benefits.”
Todd Litman, of the Victoria Transport Policy Institute, adds a cautionary note. “Road widening and traffic signal synchronization are sometimes advocated as ways to reduce traffic congestion, and therefore energy consumption and pollution emissions. However, research suggests that at best these provide short-term reductions in energy use and emissions which are offset over the long-run due to Induced Travel. Field test indicate that shifting from congested to uncongested traffic conditions significantly reduces pollution emissions, but traffic signal synchronization on congested roads provides little measurable benefit, and can increase emissions in some situations. (See: http://www.vtpi.org/tdm/tdm59.htm#_Toc193865016)
This induced demand is the reason we cannot build (widen) our way out of congestion (because widening a road induces MORE car trips that would not have occurred had we not widened). If it is agreed that we cannot build our way out of congestion (or loosen our belt to solve obesity), why do some of us think we can synchronize our traffic lights out of congestion?
The tragedy is that many communities — which have many vigorous advocates of synchronization, including “environmentalists” and other intelligent people who should know better — spend millions of public dollars to worsen transportation conditions, quality of life, air pollution, and gas consumption? In my view, proponents of synchronization are sadly wasting public dollars by moving communities further away from important community objectives.
Traffic synchronization may be popular and may seem like an irrefutably good idea by most people, but the unintended consequences described above point out that synchronization is highly counterproductive to the objective of a more sustainable, pleasant community, less pollution, less gas consumption, and more transportation choices.
My latest book, The Car is the Enemy of the City (WalkableStreets, 2010), can be purchased here: http://www.lulu.com/product/paperback/the-car-is-the-enemy-of-the-city/10905607
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.
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