Peltzman Effect

[Dr Adequate]

For those of you who haven't heard of it, Shanek has just written an article on the Peltzman Effect.

Humans ... we're even dumber than we look, aren't we?

[Mojo]

I'm a bit sceptical about "the engineers also tried the same thing with traffic lights; replacing traffic-light intersections with roundabouts resulted in intersection deaths decreasing from one every three years to none at all." For such a comparatively rare event, how long would the experiment need to run for this result to be significant?

[Dr Adequate]

That depends on how many locations you do it in. The article does say "roundabouts", plural.

[Wolfman]

Well, I would agree with this in part, but not in full.

For example, I recall when I was a teenager, a particular on-ramp to one of the highways had a very sharp turn, and the authorities set up passive traffic radar attached to a sign that posted the speed you were going at; if you went above the recommended speed limit, it went red and flashed a warning sign. (This was before the traffic cameras that actually took your picture)

Well, of course, the immediate reaction from me and all my friends was to intentionally go fast in order to get the danger sign to light up; it had exactly the opposite result from that intended.

But that said, this article says that, "a recent study on cell phone use and vehicle crashes found that increased cell phone use did not increase crashes." I'd have some questions about this. For example, this could simply mean that vehicle crashes as a whole have decreased due to other policies, but that the proportion of crashes caused by cell phone use has increased. It seems to me that there have been a number of studies done that have reached the conclusion that using a cell phone increases the risk of having an accident, I'd want more than a vaguely worded conclusion about one single study before reaching any more comprehensive conclusion.

In a business context, I think that this is particularly untrue. Companies that institute very strict regulations (and specific punishments for violating those regulations) certainly seem to decrease "risky behavior"...in fact, they tend to stifle creativity and personal initiative altogether. In regards specifically to safety, I would say that the positive impact of strict safety regulations in the workplace have significantly decreased injuries and fatalities.

So, like many things, the Peltzman Effect has some legitimate applications; but we should be very cautious in trying to extend it too far.

[Leif Roar]

I'm a bit sceptical about "the engineers also tried the same thing with traffic lights; replacing traffic-light intersections with roundabouts resulted in intersection deaths decreasing from one every three years to none at all." For such a comparatively rare event, how long would the experiment need to run for this result to be significant?

To me it seems pretty silly to compare accident rates at regular cross-roads and roundabouts directly, anyhow. They are, after all, two completely different types of traffic control mechanisms. Aren't roundabouts considered to be safer and more efficent than light controlled intersections in the first place?

[The Atheist]

For those of you who haven't heard of it, Shanek has just written an article on the Peltzman Effect.

I would have thought that the effect hadn't been sufficiently explored regarding traffic deaths/injuries to be claimed as factually as it is in SW. Seatbelts are a good example. The Peltzman Effect would claim that people are less careful, but the wearing of them makes the injuries far less severe and in the cases of low speed, virtually removes fatality as a result.

Certainly didn't work for Henri Paul (http://news.bbc.co.uk/onthisday/hi/dates/stories/september/1/newsid_2493000/2493315.stm).

I think the article is most likely correct, but there seem to be a couple of fairly lengthy bows drawn without exploring enough bases. The German/US freeway difference could equally have been simply safer vehicles. What would you drive, a Volvo or a Pinto?

Another simple expedient would be to look at enforcement practcies. At any given time, a number of enforcement officers will be engaged in catching speeding motorists. Montana's ones probably didn't sit around on their thumbs and were doing something else instead, and it could be those measures which in fact paid off with a reduced death toll.

Humans ... we're even dumber than we look, aren't we?

You will never find me disagreeing with that.

To me it seems pretty silly to compare accident rates at regular cross-roads and roundabouts directly, anyhow. They are, after all, two completely different types of traffic control mechanisms. Aren't roundabouts considered to be safer and more efficent than light controlled intersections in the first place?

This one, I think, is easy.

The vast majority of fatal crashes at traffic lights are simply cars going through red lights. Roundabout = no lights + lower average speed in the intesection.

[JonnyFive]

The article mentions insurance in passing, and in the insurance business we have a term for something that's a kind of corrollary to this that might be worth mentioning: adverse selection.

Basically, adverse selection refers to the tendency of low-quality risks to seek insurance coverage disproportionately as compared to high-quality risks. Those in poor health, for example, are far more likely to desire health insurance than those in perfect health, who may downplay their own risks due to their current situation. Similarly, older people, or those commonly in life-threatening situations may seek to obtain life insurance more than the young or those who are not generally at risk of death.

It's logical, really. It makes sense to try to obtain more insurance coverage when you need it urgently, as opposed to when you don't. If you're in perfect health, why waste money on more life and health insurance? Of course, we need to be aware of this when rating risks.

[TriangleMan]

Aren't roundabouts considered to be safer and more efficent than light controlled intersections in the first place?
There are a lot of roundabouts where I live and, compared to traffic lights, they are more efficient only up to a certain density of traffic. A traffic light is better when there is a lot of traffic.

As for accidents IMO most traffic accidents here occur at the roundabouts but the severity of damage is less due to traffic lowering its speed. Crashes at lights are rarer but more likely to be severe due to speeding.

[LordoftheLeftHand]

I'm a bit sceptical about "the engineers also tried the same thing with traffic lights; replacing traffic-light intersections with roundabouts resulted in intersection deaths decreasing from one every three years to none at all." For such a comparatively rare event, how long would the experiment need to run for this result to be significant?

Well as far as this case goes I can imagine another explanation in this situation: When you drive through a normal intersection you typically drive through at the normal speed you are traveling on the road in question (lets say 40mph). When you drive through a roundabout you greatly reduce your speed to make the turn required (lets say 15mph). While I don't have the statistics, I'll assume that a 15mph collision is much less likely to create a fatality than a 40mph collision. Furthermore I would imagine a head on collision at full speed would be almost impossible in a roundabout. I think a better comparison would be the total number of collisions recorded at the intersection instead of the severity of injuries produced there.

[Leif Roar]

I think a better comparison would be the total number of collisions recorded at the intersection instead of the severity of injuries produced there.

But that still won't tell you anything about the Peltzman effect: even if traffic lights had been security means (they're not, they're flow control means) we'd have to compare intersections with traffic lights to the similar intersections without traffic lights, and not intersections with traffic lights to roundabouts.

[LordoftheLeftHand]

But that still won't tell you anything about the Peltzman effect: even if traffic lights had been security means (they're not, they're flow control means) we'd have to compare intersections with traffic lights to the similar intersections without traffic lights, and not intersections with traffic lights to roundabouts.

Good point.

[Mojo]

That depends on how many locations you do it in. The article does say "roundabouts", plural.But is the figure of "one death every three years" the average for each intersection, or was it just one death every three years over all the intersections considered?

[Earthborn]

The article does say "roundabouts", plural.The article that Shanek uses as a source (http://skepticwiki.org/index.php/Peltzman_Effect) doesn't support that claim though. Only one roundabout is mentioned. The figures mentioned in the SkepticWiki article are nowhere to be found. And I don't think a decrease from 1 every 3 years to none in 5 years is significant.

This SkepticWiki article fits Shanek's ideology of "safety regulations kill" a bit too conveniently and certainly does not provide a very critical look.

[The Atheist]

Does anyone do quality control at SW?

[Larry Lovage]

I'm not sure if this is related to the Peltzmann effect, but some years ago I heard the theory that the safest car on the roads would be built out of cardboard and have a large spike sticking out of the steering wheel right at the driver's chest. The increasing plethora of safety features on cars had simply meant that people felt safer driving at higher speeds so that the overall injury rate had scarcely changed (although there were probably fewer deaths).

[The Atheist]

I'm not sure if this is related to the Peltzmann effect, but some years ago I heard the theory that the safest car on the roads would be built out of cardboard and have a large spike sticking out of the steering wheel right at the driver's chest. The increasing plethora of safety features on cars had simply meant that people felt safer driving at higher speeds so that the overall injury rate had scarcely changed (although there were probably fewer deaths).

Kind of an anti-Peltzman effect, but I bet it'd work!

Now, if we can just get them fitted to SUVs first...

[ImaginalDisc]

My car, the Volvo 240 wagon, is one the safest cars of the 90's. No driver deaths occured in single-car crashes in a 240 wagon from 1990 to 1994, and other categories of crashes likewise are far below average in terms of deaths.

Source (http://www.usroads.com/journals/aruj/9702/ru970207.htm)

If safety features tend to increase risky behaviors, why does the 240 wagon have such an incredible safety record?

[JonnyFive]

If safety features tend to increase risky behaviors, why does the 240 wagon have such an incredible safety record?

The factory-installed Peltzman Inhibitor Unit, I would imagine.

[geni]

Generaly deaths alone are not generaly used to measure road saftey. Numbers are so low that one bus full of kids with make a significant blip for that year. Instead killed and seriously injured is more commonly used.

[ImaginalDisc]

The factory-installed Peltzman Inhibitor Unit, I would imagine.

Oh, darn. I think I just figured out what that persistent warning light in my dash means.

[shanek]

Thank you for the criticisms. I have removed the portion on traffic lights vs. roundabouts; you are entirely correct that this is not an example of the Peltzman Effect.

[Mashuna]

I recall reading about (although I can't now find) an article regarding a study on cycling safety. This study claimed that if cyclists took advantage of visible safety measures such as wearing a helmet or flourescant jacket, drivers tended not to give them as much clearance when overtaking, presumably on the basis that the cyclist was more safety aware so could look after themselves.

Is this an example of an extended Pelzman effect, or just the normal sort?

[The Atheist]

Thank you for the criticisms. I have removed the portion on traffic lights vs. roundabouts; you are entirely correct that this is not an example of the Peltzman Effect.

How about the fact that SW seems to present the Effect as actual, when at this stage, it still appears to be very hypothetical, especially given the paucity of evidence you use in drawing the conclusions - an aberration in Montana and one Dutch study appears to be far short of what's required for proof.

The cellphone question is quite interesting and I see you've drawn on one study only. I wonder whether the parents of the dead kids we've had recently, through a spate of crashes while using the phone, would agree with it.

[Earthborn]

I have removed the portion on traffic lights vs. roundabouts;But you left something in about the removal of "traffic safety signs", not realising that this removal of traffic signs, the redesign of roads and construction of roundabouts was part of a single redesign of the traffic situation from a single philosophy. You can't take one thing out and leave something else, if you want to argue that it works for a particular reason.

I think it may very well be a Peltzman effect. This Monderman guy specifically designs roads in such a way that it scares an confuses the heck out of people, to get them to drive more carefully. I suspect however, that this is only effective because people in the Netherlands are used to very clear road design and lots of signage to tell them exactly what they are supposed to do and who has right of way. I don't think it means that in countries where traffic is not so highly regulated, safety can't be improved by more signs and clearer road design.

Here (http://www.youtube.com/profile_videos?user=tequio&p=r) is a video where you can see the traffic situations designed by Monderman for yourself. You'll need to read between the lines when he talks about some of the compromises he had to make in his designs: many people complain about the confusing traffic situations he creates. His philosophy can be summed up as "forcing people to behave more safely, by making them feel unsafe."

[The Atheist]

Surely at least part of this can now be placed into the "myth" category?



The effect can occur in reverse as well. A recent study on cell phone use and vehicle crashes found that increased cell phone use did not increase crashes. The authors attributed this effect to drivers compensating by driving more safely when they talk on their cell phones, as well as ceasing other distracting behavior.

Yeah, right. (http://www.nzherald.co.nz/section/1/story.cfm?c_id=1&objectid=10487746)

Yes, the boy had been drinking*, but this is merely the latest in a growing list of fatalities caused by cellphone usage - mostly text usage - by young drivers in this country alone.

Plainly, the study which concluded that cellphone use is fine is fatally flawed. The fact that one death can be attributable to cellphone use while driving is an increase in crashes on its own. The fact that many can consigns this report to pseudoscience.



*and note that "double the alcohol limit for his age", is only 30mg/100ml as opposed to the adult 80mg/100ml, so he wouldn't have been particularly legless.

[UserGoogol]

For those of you who haven't heard of it, Shanek has just written an article on the Peltzman Effect.

Humans ... we're even dumber than we look, aren't we?

It's entirely rational behavior. If you're safer, you have less reason to worry about being safe, which makes people not quite as safe as you would otherwise be.

I think Shanek, being a very libertarian individual, might be putting a slightly more antiregulatory spin on this than the concept deserves, though, by implying that regulations explicitly make people stupid. Wikipedia's article on the subject gives the example that if cars are easier to crash and survive, then people will crash their cars more and yet people in cars will still have less fatalities (more fatalities than one would otherwise expect, but still a net decrease) but the problem is that car crashes hurt people who aren't protected by the safer cars, like pedestrians. Which is how Peltzman himself describes it. (http://www.aei-brookings.org/admin/authorpdfs/page.php?id=1144) (He gives other examples of regulations being counterproductive in that article, but there he cites different sorts of mechanisms.)

It's a pretty neat idea, though.

[Just thinking]

For those of you who haven't heard of it, Shanek has just written an article on the Peltzman Effect.

Humans ... we're even dumber than we look, aren't we?

Actually, one might draw just the opposite conclusion ...
Speed limits have often been claimed to be a necessary highway safety regulation. However, when Montana removed speed limits on its interstates and rural highways, fatalities on those highways plummeted. Officials found that drivers responded to the lack of speed limits by being more careful and more courteous to other drivers, while only changing their speed by a few miles per hour. When speed limits were reinstated, this safe driver behavior disappeared and fatalities rose again.

It seems the drivers had a sense of what to do without the need for being told how fast to drive. I have always felt that most (the overwhelming majority) of drivers on the road will drive at reasonable speeds the traffic and conditions will permit --- and that in many cases speed limits are set too low for what would feel comfortable. This in effect causing a higher level of tension while driving; e.g.; looking out for radar traps instead of concentrating more on the driving. Also causing more speed variation among vehicles.

[a_unique_person]

I read that Toyota 4WD's, (or SUVs for people who live in other parts of the world), always let you know when the vehicle stability drive control safety mechanisms are being used. It thereby serves it's purpose, without just taking risk taking to the next level. When it's engaged, it lets out an annoying chime, thereby dissuading you from just taking advantage of it's safety enhancement feature without regard.

[bruto]

My car, the Volvo 240 wagon, is one the safest cars of the 90's. No driver deaths occured in single-car crashes in a 240 wagon from 1990 to 1994, and other categories of crashes likewise are far below average in terms of deaths.

Source (http://www.usroads.com/journals/aruj/9702/ru970207.htm)

If safety features tend to increase risky behaviors, why does the 240 wagon have such an incredible safety record?
Because it's stodgy and slow? :D

Seriously, it is a pretty stodgy vehicle, and tends to be favored by people who are already concerned about safety and utility over speed and flash. I've heard the same argument used with bicycle and motorcycle helmets, but I think it has to be taken with a grain of salt. For one thing, you have to determine the extent to which the hazard you're protecting against is dependent on unsafe behavior. Careful bicyclists can hit their heads too, after all, and the Peltzman effect might not apply, or not as reliably, when the choice of safety is optional.