CONTACTTRAFFICABOUT TOM VANDERBILTOTHER WRITING CONTACT ABOUT THE BOOK

The Invisible Hand

David Williams of the Telegraph gives a prototype vehicle equipped with Intelligent Speed Adaptation (what used to be known as a “governor”) a spin through London. The car limits speed to whatever the limit is on the segment — typically 30 mph.

This line struck me:

Like most motorists I want to be law-abiding. Up until now I’d believed I was. But this clever car exposes such self-delusions. Normally I try to keep to 30mph in town but in reality I must have been doing nearer 40 as I never drive this slowly.

Someone recently asked me, “why do people speed?” There’s no short answer to that question (I’ve got 250-page reports tackling the question), but one possibility that must be considered, in light of the above sentences, is that: They actually don’t know how fast they are going. Any number of studies have shown how drivers, particularly when the feedback is noisy — i.e., they’re sitting high up from the road, the car cabin is ultra quiet (or the radio loud), the road is very wide — routinely underestimate their speed.

As we’ve banged on here about many times before, these minor differences in urban speed, while inconsequential and almost imperceptible for the driver, can be of dramatic importance for the pedestrian or cyclist struck by a vehicle.

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This entry was posted on Monday, May 11th, 2009 at 8:30 am and is filed under Cars, Cities, Drivers, Pedestrians, Risk. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

15 Responses to “The Invisible Hand”

  1. Scott Says:

    I don’t buy the “I didn’t realize how fast I was going” argument. There’s a giant gauge on the dashboard that tells you that. It’s right in the center and it’s usually larger than all the other gauges. Are people so distracted/careless/stupid that they don’t even keep track of the speed of their vehicle, which is probably the most important aspect of driving besides keeping the vehicle in the correct position on the road?

  2. MattG Says:

    I’m going to politely disagree with Scott. What’s the very first thing you do when you see a police cruiser on the side of the road? Check your speedometer. Why? Don’t you already know how fast you’re going?

  3. doug Says:

    yeah. i think most people probably gauge their speed more from their surroundings (which always look like their passing more slowly than they really are) as well as position relative to other drivers, rather than the speedometer fourteen inches from their face.

    riding a bicycle, one gets a feel for how much impact sensory feedback has on the sense of speed. riding down a steep road at 35 or 40mph on a bike feels incredibly, dangerously, intoxicatingly fast. yet for most driving autos, it’s intolerably pokey.

  4. Mrs. Davis Says:

    Driving is like combat; hours of boredom punctuated by moments of sheer terror.

  5. Richard Says:

    I have to side with Scott. It’s a rare occasion when I don’t know how fast I’m going. Even without looking at the speedometer, I can sense if I’m speeding up or slowing down relative to whatever speed I was trying to keep. The fact is, people don’t think it’s important to obey the speed limit.

  6. Jack Says:

    We all know when we are speeding, we look to see by how much and to gauge our chances of being pulled over when law enforcement is noticed. Speeding only means a slap on the wrist in the USA while in Europe you can loose driving privileges for a month or more. They’re serious while drivers in the USA are treated like children.

  7. aaron Says:

    People want, and to some extent need, a certain amount of stimulation, if they don’t get it they zone out. It’s only a little less dangerous because at the lower speed, accidents might be less severe. Mrs. Davis’ comment drives it home, congestion and slow speeds numb the mind and increase potential for risky behavior just to fill the time.

    Also on the issue of speed, in my county they recently installed an “intelligent” traffic system. It allows the county to adjust traffic light timing. However, since they don’t co-ordinate posted speed with the timing, it makes the speed limit meaningless and induces speeding. If going the speed limit doesn’t reduces your chances of catching a red light, why bother.

  8. Chris Says:

    I’d be interested in seeing if insurance companies would put this to use. If you install this device, would your insurance rates decrease? Progressive already offered to reduce insurance rates for driving less, how about for driving less aggressively?

  9. dvan Says:

    Outside of rush hour, the average speed of vehicles in the United States is virtually always higher than the posted speed. “Five over” is a standard that you can follow coast-to-coast without receiving a speeding ticket unless you run across a speed camera.

    Members of the various governmental bodies that set speed limits are often quite open about how they set speed limits – 5 or 10 miles per hour slower than they think most people will drive.

    Many traffic safety studies demonstrate that relative speed differences between vehicles are much more likely to cause accidents than the absolute speed of traffic. If everyone is driving at 80 mph plus or minus 2 mph, the group is generally safer than if some people are driving 60 and others are driving 80.

    As far as “Intelligent Speed Adaptation” AKA a governor, I can think of dozens of times that the ability to speed up allowed me to avoid a collision, whether pulling into traffic, at an intersection or passing on a two-lane road.

    What’s going to happen to traffic if everyone’s governor limits them to 60 mph and someone decides to drive 58 mph on a two-lane road? A long line of tailgating cars leading to a giant chain-reaction of rear-end collisions.

  10. Clarence Eckerson Says:

    Oh this is a very interesting development!

  11. spe Says:

    I’m curious to know how speed limits are typically set in Europe. As a Traffic Engineer I loathe the topic of speed limits because they are so often set incorrectly at the.. um… encouragement of elected officials.

  12. Eric Says:

    @aaron,

    The public road is not the place to seek stimulation. Anyone who’s using it for such needs to have their driving privileges removed. We’ve all seen such drivers. They’re usually young, male, and first class douches.

    As the movie indicates, the scientists at Traffic for London claim that by keeping people within the speed limit will lower accidents by 10%. Fewer accidents and at lower average speeds — sounds like a winner.

  13. Grant Johnson, PE, PTOE Says:

    Speeding is relative. Speed limits are set at 85th percentiles of a sample of at least 100 drivers (radar speed survey). So the limits are set based on what the majority of people actually drive, because it is common sense that most people want to be safe. So it is my belief that most people will drive a safe speed. That’s the traffic engineering science.

    When people speed, they are in that 15% group at the top, and they are either law breakers or they are in a hurry, which also means that they are a law breaker. The only sure way to fix a speeding problem is enforcement and hit them in their pocketbook. It really does slow people down, and they start watching for those cops, and that slows them down. Really does.

    <a href=”http://prismengineering.blogspot.com/2009/05/boy-racers-have-already-knocked-wall.html”?http://prismengineering.blogspot.com/2009/05/boy-racers-have-already-knocked-wall.html

  14. aaron Says:

    Does it improve safety?

  15. Jimbo Says:

    We find it so easy to speed because as noted above, speed limits are set below the design speed of the roadway. People drive at a speed that feels comfortable on a roadway, not at the speed limit. I find myself driving below the speed limit on some roads and above on others, mainly because of the design.

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Traffic Tom Vanderbilt

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.

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