Wednesday, August 11, 2010

Spontaneous Order, Traffic Lights, and the Peltzman effect

There's a subset of bureaucrats and regulators who want us to believe that the only thing separating us from chaos/imminent disaster is another rule or law. So what happens when you turn off the traffic lights? From John Stossel at

In some cases, traffic moves better and more safely when government removes traffic lights, stop signs, even curbs.

It's Friedrich Hayek's "spontaneous" order in action: Instead of sitting at a mechanized light waiting to be told when to go, drivers meet in an intersection and negotiate their way through by making eye contact and gesturing. The secret is that drivers must pay attention to their surroundings — to pedestrians and other cars — rather than just to signs and signals. It demonstrates the "Peltzman Effect" (named after retired University of Chicago economist Sam Peltzman): People tend to behave more recklessly when their sense of safety is increased. By removing signs, lights and barriers, drivers feel less safe, so they drive more carefully. They pay more attention.

In Drachten, Holland, lights and signs were removed from an intersection handling about 30,000 cars a day. Average waiting times dropped from 50 seconds to less than 30 seconds. Accidents dropped from an average of eight per year to just one.

On Kensington High Street in London, after pedestrian railing and other traffic markers were removed, accidents dropped by 44 percent.

"What these signs are doing is treating the driver as if they were an idiot," says traffic architect Ben Hamilton-Baillie. "If you do so, drivers exhibit no intelligence."
Sure enough, here's the experience of a small town in Britain (via Marginal Revolution):

Marginal Revolution goes on to quote a profile about "an unassuming Dutch traffic engineer showed that streets without signs can be safer than roads cluttered with arrows, painted lines, and lights" in the Wilson Quarterly. The article describes a busy intersection where traffic lights are removed:
At the town center, in a crowded four-way intersection called the Laweiplein, Monderman removed not only the traffic lights but virtually every other traffic control. Instead of a space cluttered with poles, lights, “traffic islands,” and restrictive arrows, Monderman installed a radical kind of roundabout (a “squareabout,” in his words, because it really seemed more a town square than a traditional roundabout), marked only by a raised circle of grass in the middle, several fountains, and some very discreet indicators of the direction of traffic, which were required by law.

As I watched the intricate social ballet that occurred as cars and bikes slowed to enter the circle (pedestrians were meant to cross at crosswalks placed a bit before the intersection), Monderman performed a favorite trick. He walked, backward and with eyes closed, into the Laweiplein. The traffic made its way around him. No one honked, he wasn’t struck. Instead of a binary, mechanistic process—stop, go—the movement of traffic and pedestrians in the circle felt human and organic.

A year after the change, the results of this “extreme makeover” were striking: Not only had congestion decreased in the intersection—buses spent less time waiting to get through, for example—but there were half as many accidents, even though total car traffic was up by a third.
Of course, regulations aren't the source of the Peltzman effect where technology designed to make us safer does the opposite - also from Marginal Revolution:
The NHTSA had volunteers drive a test track in cars with automatic lane departure correction, and then interviewed the drivers for their impressions. Although the report does not describe the undoubted look of horror on the examiner’s face while interviewing one female, 20-something subject, it does relay the gist of her comments.

After she praised the ability of the car to self-correct when she drifted from her lane, she noted that she would love to have this feature in her own car. Then, after a night of drinking in the city, she would not have to sleep at a friend’s house before returning to her rural home.
Update (Aug 17): The Antiplanner (Freakonomics)

Update (Aug 23): Solutions for traffic jams (

Update (Sept 23): To tame traffic, go with the flow: Lights should respond to cars, a study concludes, not the other way around (


yoimi.see.yin said...

Thanks for the very good article and interview. Who's involved in this study? I'd like to know more about this experience.

Unknown said...

In the Washington DC area of the US, it seems that everything to control traffic has been tried. Signs of all type, traffic circles, speed tables, etc. to various affects on traffic, pedestrians, and businesses. Now the new trend is traffic cameras, and un-marked cars. However, it seems to me that the red queen effect is always the dominant stakeholder. (You have to run fast just to stay in the same place). People are smart, crafty, and resistant to control. The question, in my view, is there some fundamental error in the design of traffic control systems that engenders such solid resistance? As a driver I feel that the error may be the inaccuracy, general nature, or one size fits all circumstances of most traffic control systems. I mostly drive at night, on deserted streets, but I am still forced to behave as if it were rush hour. Yet when the roads are full and its pouring rain, I still feel forced by other drivers to maintain a reasonable speed. As automation finally reaches the drivers seat I hope that we will be able to move toward "honest" traffic control which is condition based.

Until that Utopian future, of emotionless robot drivers, emerges the engineers at my company Gravitational Systems Engineering have devised several smart traffic control devices that are worth consideration. Our devices called speed sponges, appear as green speed bumps but they are completely soft and collapse when encountered at safe speeds. However, when one of these devices is triggered by a speeder, it remains firm and slows the vehicle. They come in both embedded and surface mounted models, but in each instance they can not only stop unsafe behavior based upon road conditions, but they also force drivers to think.

Gare Henderson,

Gravitational Systems Engineering, Inc.