Friday, February 8th, 2008

Are “Safer” Roads More Dangerous?

I know I’ve mentioned this before, but it is worth bringing up again. Wired Magazine published an article in 2004 about Dutch traffic engineer Hans Monderman, and a trend he started to improve roadway safety by making things appear more dangerous.

The theory goes like this. Putting up signs and designing to remove all possible things that interfere with traffic makes roads appear safer than they really are. Drivers react by becoming more relaxed and less vigilant, resulting in accidents. But if you make roads appear dangerous, for example, by removing signs, people pay more attention and there are less accidents.

Monderman has several real life examples.

Riding in his green Saab, we glide into Drachten, a 17th-century village that has grown into a bustling town of more than 40,000. We pass by the performing arts center, and suddenly, there it is: the Intersection. It’s the confluence of two busy two-lane roads that handle 20,000 cars a day, plus thousands of bicyclists and pedestrians. Several years ago, Monderman ripped out all the traditional instruments used by traffic engineers to influence driver behavior – traffic lights, road markings, and some pedestrian crossings – and in their place created a roundabout, or traffic circle. The circle is remarkable for what it doesn’t contain: signs or signals telling drivers how fast to go, who has the right-of-way, or how to behave. There are no lane markers or curbs separating street and sidewalk, so it’s unclear exactly where the car zone ends and the pedestrian zone begins. To an approaching driver, the intersection is utterly ambiguous – and that’s the point.

Monderman and I stand in silence by the side of the road a few minutes, watching the stream of motorists, cyclists, and pedestrians make their way through the circle, a giant concrete mixing bowl of transport. Somehow it all works. The drivers slow to gauge the intentions of crossing bicyclists and walkers. Negotiations over right-of-way are made through fleeting eye contact. Remarkably, traffic moves smoothly around the circle with hardly a brake screeching, horn honking, or obscene gesture. ‘I love it!’ Monderman says at last. ‘Pedestrians and cyclists used to avoid this place, but now, as you see, the cars look out for the cyclists, the cyclists look out for the pedestrians, and everyone looks out for each other. You can’t expect traffic signs and street markings to encourage that sort of behavior. You have to build it into the design of the road.’

This theory is being applied in many places across Europe and the US. I think it is in intriguing because it is based on modern knowledge of human psychology, not traditional fluid dynamics based engineering, where everything is about vehicle flow.

It applies to things other than roads as well. Any system with extensive safety measures and procedures becomes at some point prone to catastrophic failure. We’ve seen this in situations as diverse as the recent subprime crisis (where instruments designed to spread and thus mitigate against default risk actually destabilized the financial system), nuclear power accidents and of course 9/11, where security and hijack procedures led to routinized behavior that was exploited to horrific effect.

That’s not to say that we should remove all safety measures and devices. But the instinctive reaction to a problem is always to add more layers of protection, and at some point, this takes us backwards. I think this type of understanding of human behavior is something we should definitely take account in the design of roads and other systems.

As a decidedly anti-safety aside, check out Wired’s coverage of Alex Roy’s incredible New York to Los Angeles “cannonball run” in only 32 hours, 7 minutes.

Topics: Transportation

2 Responses to “Are “Safer” Roads More Dangerous?”

  1. thundermutt says:

    We have two pretty good examples of this in Indianapolis, and they actually predate the Monderman article by 20+ years: Monument Circle and the 200 block of East Market Street (between the City-County Building and City Market).

    Monument Circle is the better example, as there are no traffic markings, stop signs, or yield signs. There are bollards to protect the monument itself and the exclusive pedestrian zone around it, as well as curbs and curbside parking, so it’s not a perfect example, but it’s as close as you’ll find in the center of a major US city. (Based on the city’s traffic count maps, the circle gets about 20K vehicles a day. 200 East Market gets about 8K.)

    Another obvious fact: brick or textured streets may be hard for DPW to keep clean and maintain, but they definitely slow traffic enough to promote “negotiation”.

    I think that’s one place where Carmel missed the mark with its roundabouts. Some of them (especially on Hazel Dell Parkway) are merely high-speed “swerves” that are akin to a plenum or manifold in mechanical systems (to stick with your fluid dynamic simile). Rough pavement would have slowed traffic more.

  2. Crocodileguy says:

    The Hazell Dell roundabouts are only swerves for the people who do not stay in their lane inside the roundabout.

    I do agree, though, that Carmel needs to add more textured pavement to them.

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