Traffic Signal Synchronization, Ctd.

 

MinnPost file photo by John Noltner

I was recently quoted in an article on traffic signal synchronization – an ongoing project in Minneapolis right now. I have a contrary view to conventional wisdom on this topic as I have been quoted in the article and expressed in greater detail here.

Communities like traffic signal synchronization because it is smart technology that can reduce congestion and increase traffic flow without making any geometric changes to the roadway system. My argument is that these technologies work a little too well – they actually create induced demand  which in the longer term leads to more congestion and air pollution and poor land use decisions. I’ll stand by my quote in the article in that traffic signal synchronization is a solution that becomes a victim of its own success.

Traffic Signal Synchronization – Why not?

I was having a debate over John Hilkevitch’s article a while back in the Tribune about synchronized traffic signals with a friend of mine. My friend was surprised that this technology, most impressively shown in the movie, The Italian Job, was not widely deployed in many major cities such as Chicago. Alas, we still rely on, in some cases, 1950s technology to power our traffic signals. The essence of his thinking was why had it taken so long to roll out this technology given its substantial benefits.

My response, colored by my experience (cynicism?) in transportation, was to be skeptical. Traffic engineering has long been full of promises on solving road congestion, with many solutions worse than the problem. When roads have been widened or new roads built, induced demand has been the result. If we make all of our signals “smart” and easy for people to drive in the city, what happens then? We’ll see a mode shift away from alternative transportation options as people discover that synchronized traffic signals make driving easier, thus increasing demand for driving. As Todd Litman notes,

Field tests 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 (Frey and Rouphail 2001).

Making driving easier brings all the negative externalities to the fore: increased auto emissions, gas consumption and pressure on land uses to accommodate cars. Thus, while traffic signal synchronization seems like a good idea, the unintended consequences are likely to make the existing traffic congestion status quo even worse.

Update: Dom Nozzi, making many of the same points, explains this in better detail here.