Seat Belts Work

Yesterday, James Annan pointed us to a literature (see here and here) suggesting seat belt (or air bag) use does not actually saves lives.   Yes, all else equal those wearing seat belts are more likely to survive accidents, but those who know they are better protected also compensate by driving less safely.  The net effect is theoretically ambiguous, and the empirical data was long not clear.   

Looking at Wikipedia seems to support skeptics, as skeptic arguments cited there are much stronger than the pro arguments, which are mainly government sources that don’t seem to address skeptical points.  And since I’m pretty skeptical about the effect of medicine on health, it seemed natural for me to embrace this skeptical argument. 

But I dug deeper and found this 2003 Review of Economic Studies article (ungated here):

Using a unique panel data set on seat belt usage in all U.S. jurisdictions, we analyze how such laws, by influencing seat belt use, affect the incidence of traffic fatalities. … We find that such usage decreases overall traffic fatalities. The magnitude of this effect, however, is significantly smaller than the estimate used by the National Highway Traffic Safety Administration. In addition, we do not find significant support for the compensating-behavior theory, which suggests that seat belt use also has an indirect adverse effect on fatalities by encouraging careless driving.  …

Our estimate of the potential savings in lives from increased seat belt usage are less than half of the estimate used by the National Highway Traffic Safety Administration (NHTSA). … Our estimates indicate that the national usage rate would increase from 68% to 77%, and 500-1200 lives would be saved annually, if all states now having secondary enforcement moved to primary enforcement.

Of course I’m always worried about data mining and publication biases toward getting the results authors expect to see.  But I don’t see any obvious indications here, and the results seem robust to several variations.  So I’ll tentatively conclude seat belts do save lives.  Of course this is not to say this gain is worth the cost in terms of whatever it is that makes drivers reluctant to wear seat belts.   

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  • Silas

    To be be honest, I’ve never understood why the “compensating behavior” theory got much credit to begin with. In driving school, the seatbelt video spend most of its time debunking arguments related to the effectiveness of seatbelts, and those arguments (that they’re debunking) sound like rationalization at its worst:

    “The last place I want to be in an accident is in the car.”
    “If I crash, I’ll just brace myself.”

    So apparently, the general public:

    -Doesn’t understand how effective seatbelts are (what research of resistance to wearing them shows), but
    -Believes it gives them an aura of protection that would justify noticebly less safe driving (the compensating theory), but
    -Still doesn’t wear them (evidence on driver behavior).

  • JWR

    The theory that those wearing seatbelts tend to drive more recklessly, and that those w/out seatbelts, seems extremely implausible. The people I know who don’t wear seatbelts (my sister, a co-worker, to name two) are if anything more reckless than the average driver. Their failure to wear a seat belt is of a piece with a general tendency to ignore risk and act cavalierly. Similarly, most people (nearly 80%, it appears) do wear seat belts, and for most of them I would guess putting on the seat belt is a nearly involuntary activity. It seems implausible to imagine that such a routine, near-involuntary activity triggers more reckless driving.

    I realize it’s important to test intuitions with data, and if I saw robust enough data, I could be persuaded that this effect exists. But barring that, I am highly skeptical of this effect.

  • michael vassar

    In Kazakhstan there are laws mandating seatbelts, but people consider this to be silly so they disable the seatbelts in their cars and drape a the top over their bodies so that they won’t be hassled by cops with seatbelts as an excuse. This is obviously an instance of going to significant effort to avoid seatbelts. If questioned on why they do it, they don’t have much by way of explanation, though they talk about how silly or weird foreigners are in this respect. I remain fairly dumbfounded by this custom.

  • Robin, regarding seat belt debates, among others which effect your average person: are there a few easy to remember, simple rules of thumb that an average person might reasonably apply to get a sense of whether what he or she is reading or hearing is probably trustworthy?

  • If the theory is that people react to perceived safety by getting more reckless, the obvious solution is to force people to do something that looks really unsafe, but isn’t as unsafe as it seems. For example: most Americans I know who drive in Britain get used to it within a day or so, but they always drive under the speed limit and are quite cautious. If we forced all Americans to drive on the left, they’d drive much more safely.

    That, and we could force auto manufacturers to 1) put secret safety mechanisms in their cars, and 2) to stop advertising how safe they are.

  • Bob

    I think seat belt use represents a general bias that I perceive many people having when faced with a decision that has concentrated up front costs and long-term diffuse benefits. Seat belts are uncomfortable initially and the “cost” on that first trip certainly exceeds the expected benefit on that trip. So a significant fraction of the population never wears belts. Once a driver gets used to wearing belts it seems like the cost would reverse (it would be initially uncomfortable, although less so, to stop wearing) and it would be easy to keep wearing.

    While this seems like this would “justify” paternalistic laws, if you believe in those sorts fo things, I’m not so sure. Is the outcome unambiguously better? I mean, if you get used to a speck being put into your eye daily, you might find it initially odd, or even a bit uncomfortable, for the specks to stop. But once you got used to no specks, wouldn’t you be better off? How can we be confidant that requiring 100m people to wear uncomfortable belts, even if they are used to them and don’t complain, is worth saving X lives? And it’s *much* worse at the margin. Certainly safety does not dominate comfort absolutely – I don’t know *anyone* who actually behaves that way.

    BTW, I wear seat belts.

  • The Wikipedia bias toward skeptical arguments disturbs me.

  • Recovering irrationalist

    For controversial topics, I always check the talk page too. There’s often daft arguments and bias there, but it’s usually two-sided, and worth it for the good arguments for and against.

  • douglas

    When I worked in a hospital emergency room there was no doubt that people who had been wearing seat belts in an accident were much more likely to be repairable than those that hadn’t. (Full recovery vs. ending up hideously disfigured or paralyzed, for example)
    Saving lives is not the only aspect that needs to be considered.
    I don’t like seat belt laws, too paternalistic, but I wear one always, and would recommend you do the same.

  • Silas, most people wear seat belts, so most people think they protect.

    J, the claim is about how individuals vary their behavior with protection, not about the correlation across different personality types.

    Mike, look to most recent publications in top journals.

    Eliezer, me too.

  • Silas

    Silas, most people wear seat belts, so most people think they protect.

    Or do it out of force of habit, or want to signal that they care, or want to placate passengers, or want to avoid attention from law enforcement.

    For the compensating-behavior theory to hold, you would have to believe that the people *who only wear seat belts because it’s the law* also believe that the seatbelts make them so safe as to justify reckless driving, and yet still don’t wear them. Like JWR, I’m open to being convinced by the appropriate data, but that’s an implausible believe set for an individual to hold.

    Imagine if I told you that a group of people, Locketeers, believe that if you wear a special locket, you can’t die, and that they act without concern for personal safety while wearing them, but never actually wear them unless the law requires it.

  • Brandon Reinhart

    Silas, your post immediately made me think of my Alcor necklace. I am an Alcor member. I wear my necklace all the time, which contains the following inscription:

    front: Med. Hx. call 24 hrs (number) or collect (number) in case/death see reverse for biostasis protocol. reward. (my id)

    back: call now for instructions / push 50,000 U heparin by IV / and do cpr while cooling with ice to 10c-keep ph 7.5 / no embalming / no autopsy

    Given the current state of cryonics, it’s unlikely that this protocol will result in a viable brain, but it can’t hurt. I believe that wearing the necklace slightly increases my chances of being viable for resuscitation. However, although I wear the necklace I don’t act in a way to necessarily prolong my life significantly like some extensionists. I’m not into supplements. I work out, but I don’t do regular blood evaluations. I stay healthy, but not I’m not adverse to rollercoaster rides or boating or air travel. I like beer and the occasional cigar. It might be that avoiding air travel and very carefully regulating my blood’s contents and never touching another cigar would increase my chances of a clean death and a viable resuscitation more than wearing the necklace. Am I being irrational?

    How am I any different from a locketeer?

  • Shouldn’t cops be preventing real crimes instead of forcing people to wear seat belts? What about the opportunity cost of cops (judges, and related personnels) getting distracted from their real job?

  • Silas


    Am I being irrational?


    How am I any different from a locketeer?

    You wear your immortality device despite no legal requirement to do so. Also, you do not act abnormally recklessly when wearing it.

  • Jor

    I’ll just second what douglas said.

  • Michael,

    my dad also used to drape the seat-belt over his shoulder without locking it. He was afraid of being stuck in the car and have the car go up in flame. In fact, I once was in an accident with him on the highway and we both rushed out of the car as soon as the car stopped. Seeing the oncoming traffic try to slow down was quite scary.

  • outeast

    unit, I think you’re describing a textbook case of Too Many Movies syndrome…

    I continue to be dumbfounded by the anti-seatbelt lobby. It really seems to me that much seatbelt defiance is based on a principled objection that All Paternalism* Is Evil, regardless of the actual degree of constraint and the actual societal impacts thereof. I find such ideological absolutism pretty weird in a distinctly fuzzy world.

  • It’s worth bearing in mind that the USA is not the world: countries with a higher proportion of cyclists and pedestrians may find that the cost to these road users is higher. IME many of the “anti-seatbelt lobby” are actually the pro-cycling (maybe also pro-pedestrian) lobby.

  • James, note the study I’m citing suggests seat belts do not in fact hurt cyclists and pedestrians.

  • J Thomas

    Here is a different rationale for seat belts resulting in reckless driving.

    Maybe one of the main things tha discourages reckless driving is traffic fatalities. When somebody you know dies in an auto accident that’s sobering and cause for extra caution. But the longer you go when no one you know has died that way, the more it wears off.

    There are various things that work like that. I’ve heard that once upon a time, the year after a big hurricane it was impossible to get hurricane insurance on the coast. But then in later years it would be available but expensive, and each year the price would drop until another hurricane did big damage.

    As a rule of thumb, most people “know” about ten thousand people, and they “know well” about a thousand. There are around a thousand people like your dentist and your barber, your son’s 2nd grade teacher, people you might not exchange christmas cards with every year but that you think of as knowing. There are ten times that number that you “know”, that you’d recognise their names etc. When a year goes by and you don’t hear about any of them dying in an auto accident, it’s lulling.

    By this theory it isn’t seat belts that cause reckless driving. It’s auto safety that causes reckless driving. The immediate benefits of reckless driving balance out against the risks, and the risks seem lower when nobody you know is dead or maimed.

    Things that get a lot of publicity about strangers are like friend-of-a-friend stories or soap operas etc — they’re even less real that TV characters or politicians because you’ve never identified with them before, they’re just stories. People you know are real.

    I don’t know how true this is but it’s more plausible to me than the one that goes reckless people don’t believe in seatbelts and don’t wear them but they’re more reckless because they wear them.

  • outeast,

    sorry, my dad never watched Hollywood movies. And of course I buckle up because it’s the current norm, but in fact I should probably also wear a full football uniform, that would really work.

  • J Thomas

    “my dad also used to drape the seat-belt over his shoulder without locking it. He was afraid of being stuck in the car and have the car go up in flame. In fact, I once was in an accident with him on the highway and we both rushed out of the car as soon as the car stopped. Seeing the oncoming traffic try to slow down was quite scary.”

    One time a car I was convoying with was involved in a head-on collision. The two people in the back seat were not wearing seatbelts but luckily the front seats stopped them with little injury except a few broken bones. The front seatbelts however suffered the force not only of two bodies but also the impact from two more. They both jammed. The driver was jammed against the steering wheel with barely enough room to breathe, and his chin ws cut on the wheel. Also his head had hit the windshield and crushed the safety glass into a head-shaped pattern. This came from some combination of the steering wheel buckling, and him getting thrown up and over it, and so on. I was glad he didn’t wind up impaled on the steering wheel with his head sticking through the windshield. That would have been scary. We got his wife out of there just by cutting the stuck seatbelt and helping her out, but the driver was truly stuck, his door was crushed shut and one broken ankle was caught in the wreckage. It would have been very unfortunate for him if he had been thrown through that windshield since his ankle would definitely not go with him. He breathed easier after I cut his seatbelt, and then he had to wait for the EMTs to get there and cut the car away from him.

    If you use seatbelts it’s good to have a sharp blade in a handy spot so you can cut the seatbelts after an accident if they are stuck. The safest place to keep the sharp blade is in another vehicles, but you need to make do however you can.

    If you don’t use seatbelts then after the same accident that would jam a seatbelt you are likely to require no assistance at all.

  • JS

    You need to look not just at fatality rates, but the severity of nonfatal injuries. Having spent some years as a EMT and vehicle extrication technician, I’d say there are a lot of collisions that would be fatal with or without seatbelt, but there are many more in which the seatbelt is the difference between minor and major injury.

  • Robin,

    Nevertheless, the Isles report surveyed results obtained in 8 different countries and came to quite different conclusions.

  • bla

    Obviously you should get one of those little seatbelt cutting things. They can be mounted in the car and contain and razor inside a sort of safety case so its impossible to cut yourself with it. They also are often flashlights and windowbreakers.

  • J Thomas

    Bla, that’s a good idea. Also, make sure your after-accident tool is mounted so that it’s easy to get to, protected, and won’t become a projectile.

    But most people don’t plan ahead that far. Most people, instead of planning for what to do after a big accident that leaves them partly helpless, instead depend on the kindness of strangers.

    And it’s far easier to keep tools securely fastened in the trunk that could be useful to help others, than it is to arrange things so you can use them to help yourself after the unpredictable damage of a car wreck.

  • ChrisA

    The problem of people acting against their own clear self interest (like not wearing seatbelts) has puzzled me for a long time. I have run big construction projects in the past (thousands of people), and I have dictated that people use safety measures, such as harnesses when working at heights. It was amazing how many people would try not to use them, we even had to make it a firing basis. Now the people involved had a clear incentive to use the safety systems provided (I would fire them if caught them even if they didn’t accept the safety argument), and absolutely no benefit to not using them (they got paid the same even if they did their work faster by not using the systems), so why didn’t they use them? There were all sorts of rationales given by the people concerned when we did catch them, none of them consistent, just like the arguments of people not wearing seatbelts. I concluded that there was a status signalling thing going on, they saw my dictate that they use safety gear as a status thing by me (or by my subordinates), a way to show who was boss, and their way of challenging this status and improving their relative status was to not do as I was asking. I think this is why a lot people don’t wear seatbelts, they are showing the “man”.

    I managed to get good compliance on my sites by a mixture of incentives (we paid a bonus to everyone on the site if everyone wore their gear, creating lots of policemen and some peer pressures) plus the threat of dismissal. Not sure how to apply this to the seatbelt debate though.

  • J Thomas

    ChrisA, I have never worked high iron myself and I’ve talked for less than 50 hours with people who have. But I wonder if your “status” explanation might have another dimension too. Maybe they feel like people who can do the work without the harness are special in ways that people who can’t are not. That they are real men who deserve their pay. They could perhaps see it like being forced to put the training wheels back on their bicycles.

    It would be hard for them to explain to you, if that was true. A real C programmer who got hired to do scripting with a bunch of script kiddies might feel similarly, but he couldn’t possibly get away with sneaking C code into the product without permission.

    People care about their sense of identity first, before anything else. When ironworkers have already accepted that they face death every day, it’s hard for them to back away from that.

    This idea makes sense from what I know, but I don’t really have enough direct experience to judge it.

  • ChrisA

    J Thomas

    Certainly true that there was a macho element to it. I can understand the macho motivation, but my real surprise is that it is strong enough to make people take serious risks.

    Btw – properly using safety harness means that there is no real risk of death. On my jobs I only ever had one fatality (in many millions of manhours) and that was nothing to do with high rise work.

  • Chris, status and dominance signaling can plausibly explain a lot of paternalism behavior, and can plausibly be very strong.

  • J Thomas

    ChrisA, if a man talks like he’s macho but he refuses to take serious risks, doesn’t that mean he’s really a wimp who’s just pretending?

  • Gil

    Seatbelts can infringe and corrupt the drivers ability to operate the vehicile safely. Safe driving has precedent over the potential of an accident. The driver should have the right of being “Captain of His Ship” when determining if the use of a seatbelt is obstructing and resisting his safe operation of the car. Current seatbelt laws do not differentiate between driver and passenger and is constitutionally invalid. We have the right to protect ourselves from having the accident, and not depend on the after the fact belt.