Wear a Helmet While Driving a Car

post by James_Miller · 2015-07-30T16:36:37.768Z · score: 60 (50 votes) · LW · GW · Legacy · 117 comments

A 2006 study showed that “280,000 people in the U.S. receive a motor vehicle induced traumatic brain injury every year” so you would think that wearing a helmet while driving would be commonplace.  Race car drivers wear helmets.  But since almost no one wears a helmet while driving a regular car, you probably fear that if you wore one you would look silly, attract the notice of the police for driving while weird, or the attention of another driver who took your safety attire as a challenge.  (Car drivers are more likely to hit bicyclists who wear helmets.)  


The $30+shipping Crasche hat is designed for people who should wear a helmet but don’t.  It looks like a ski cap, but contains concealed lightweight protective material.  People who have signed up for cryonics, such as myself, would get an especially high expected benefit from using a driving helmet because we very much want our brains to “survive” even a “fatal” crash. I have been using a Crasche hat for about a week.


Comments sorted by top scores.

comment by PhilGoetz · 2015-07-31T17:34:46.561Z · score: 15 (15 votes) · LW(p) · GW(p)

I used to wear a helmet while commuting in the DC area. I think I was the only one. I do wonder whether it might increase my risk of neck injury, because it's difficult to find a helmet that doesn't push your head too far forward, especially with the new car seat designs that all put the whiplash backrest too far forward for comfort.

In a small town, it's more of an issue, because people will recognize you. But on the beltway of a major city, who cares? If they think I'm crazy, they'll just give me more space.

I stopped because I decided it was more important to wear a painter's respirator when driving on the DC beltway. This greatly reduced the number of headaches I got while driving. It's a little awkward to wear both.

comment by btrettel · 2015-07-31T22:46:53.104Z · score: 2 (2 votes) · LW(p) · GW(p)

Interesting. I tried a dust mask before when riding my bike because I was annoyed by breathing car exhaust. I should not have been surprised by how much harder it made breathing in general in retrospect. Perhaps a mask with minimal filtering would be okay, but anything more makes breathing very difficult. Such masks are not designed for when you need more oxygen than normal, and such a mask might not even be possible. You might need something like a SCBA.

comment by sumguysr · 2015-09-07T21:06:47.598Z · score: 3 (3 votes) · LW(p) · GW(p)

A quick google for "high flow dust mask" reveals several options in this exact niche, including designs especially for bikers and also ATV riders.

comment by btrettel · 2015-09-08T22:14:30.893Z · score: 1 (1 votes) · LW(p) · GW(p)

Thanks for highlighting that. I'll have to try some of these out.

Edit: Respro seems to be the dominant brand.

comment by PhilGoetz · 2015-08-01T01:10:07.546Z · score: 3 (3 votes) · LW(p) · GW(p)

You'd probably need SCUBA to keep out carbon monoxide. A dust mask is hard to breathe thru because you have a small surface area that you have to force the air thru. A respirator has a "fractal-like" filter that gives the filter a much larger surface area.

comment by CBHacking · 2015-08-07T04:44:14.571Z · score: 1 (1 votes) · LW(p) · GW(p)

Speaking as a SCUBA diver, the equipment is not designed to handle high airflow (such as you need when working hard on a bicycle), so even if the air tank itself wasn't a problem you'd need, at a minimum, a heavily-adjusted second-stage (the one with the mouthpiece) regulator. Possibly a different regulator set altogether. On the other hand, one of the design considerations of a second-stage reg is that the purge valve needs to resist water pressure, including the pressure of swimming; air would generally not have that problem (and you probably wouldn't have any need for a purge anyhow).

Even basic filter masks can cut down on particulate air pollution by a lot. I've spent some time in places with truly horrific air quality - the kind that makes LA seem clear and fresh-smelling - and a lot of people wear something over their face, even just a strip of cloth, when they go out (and sometimes also at night or even all the time). I don't know how practical they'd be at filtering out anything likely to cause headaches in traffic, and they're not terribly comfortable to wear, but it might be an option. Of course, in the US, the most common reason you see everyday people wearing something like that is if they're sick and don't wish to spread germs from their breath / sneezes, so people may be reluctant to shake your hand...

comment by Gav · 2015-07-31T13:44:43.274Z · score: 11 (11 votes) · LW(p) · GW(p)

Hmm.. wait a tic. Helmets absorb shock if your head hits something. On the motorcycle that's pretty much anything around me. But in the car, what exactly can my head hit?

I drive a recent model vehicle, and there's at least two* airbags around the driver. I can't think of any unprotected objects that my head could strike, that a helmet would help deal with. Plus if I wear a helmet, the added mass my neck supports is going to make it more likely to suffer whiplash, surely?

Not to mention that helmets seem to be designed to stop large accelerations over very short distances (i.e. soft-ish foam a couple of cm thick) whereas airbags are designed to act gently over much longer distances (a pre-perforated membrane that absorbs the blow and deforms over, I'm guessing like 20cm?)

I'm guessing that racing drivers wear helmets because in racing conditions debris is more likely to enter the car, the driver be thrown out of the vehicle, or the car will be deformed/destroyed when struck by another race car at 200km/h. Also the balaclava has a role to mitigating fire/burn risk from fuel spills.

I'm also sign(ing) up for cryonics, and want to make darn sure the lump of tissue between my ears isn't broken, but at the moment I can't see a reason helmets in cars would be a net positive.

*Just checked the web, out of curiosity. I apparently have "Driver and front passenger Advanced Airbag System" and "Driver and front passenger seat-mounted side airbags, driver knee airbag, and front and rear side curtain airbags". So that's 4 airbags that will cover just the driver.

comment by James_Miller · 2015-07-31T15:23:47.678Z · score: 5 (7 votes) · LW(p) · GW(p)

Something is causing a huge number of Americans to " receive a motor vehicle induced traumatic brain injury every year." I agree with you about a helmet's mass being a problem, but the Crasche hat is very light.

comment by Lumifer · 2015-07-31T15:45:00.793Z · score: 5 (5 votes) · LW(p) · GW(p)

Something is causing a huge number of Americans to " receive a motor vehicle induced traumatic brain injury every year."

Something like being hit by a car? Pedestrians (70-80K deaths & injuries per year) and cyclists (~50K deaths and injuries per year) are very likely to get TBI in an accident.

I think that if you are inside a car and are wearing a seatbelt the usefulness of a helmet is doubtful.

comment by gwern · 2016-01-17T00:42:58.957Z · score: 4 (4 votes) · LW(p) · GW(p)

The cited stat ultimately comes from

  • National Center for Injury Prevention and Control. Traumatic Brain Injury in the United States: Emergency Department Visits, Hospitalizations, and Deaths. Atlanta, GA: Centers for Disease Control and Prevention; 2006. http://stacks.cdc.gov/view/cdc/13379/cdc_13379_DS1.pdf

As you surmised, the car stat includes everyone related to cars:

Motor vehicle–traffic includes the following external causes of injury: occupant, motorcyclist, pedal cyclist, pedestrian, other and unspecified person involved in a motor vehicle–traffic incident.

Fortunately, they also break out the numbers for both TBI injuries and deaths by those subcategories:

  1. "Table 10. Average Annual Numbers, Rates, and Percentages of Traumatic Brain Injury-Related Hospitalizations, by Age Group and Specific Motor Vehicle–Traffic (MVT) External Causes, United States, 1995–2001" (subcategories: "MVT—Occupant", "MVT—Motorcycle", "MVT—Pedal Cycle", "MVT—Pedestrian")

    MVT-Occupant: average annual rate of 42,000 hospitalizations/injuries ("Note: In-hospital deaths were excluded.")

  2. "Table 15. Average Annual Numbers, Rates, and Percentages of Traumatic Brain Injury-Related Deaths, by Age Group and Specific Motor Vehicle–Traffic (MVT) External Causes, United States, 1995–2001"

    MVT-Occupant: 8,819 deaths

They note generally there is underreporting; another paper, after noting that there don't seem to be any decreases in TBI rates post-2001, says that 25% of TBI cases who are knocked unconscious don't seek medical attention, and 14% of those cases seek attention where it wouldn't be recorded in the stats. So that's >42000 injuries and 9k deaths to people inside a car.

Some further reading:

comment by gwern · 2016-01-17T02:44:22.684Z · score: 10 (5 votes) · LW(p) · GW(p)

OK, so 42k injuries/9k deaths is sobering, but does it justify wearing a driving helmet? I've been curious about this topic and also walking helmets for a while and now that I have my own car again (ironically, given the datasets here, an old 2000 car), the topic of reducing car risks is also of some personal relevance. I'm going to give a stab at a quick and dirty decision analysis here to get an idea of how the case for driving helmets look.

First, we want to convert the absolute numbers to a probability of injury/death per mile driven:

So if you drive 5000 miles (roughly what I currently drive per year), then you have a risk of death or injury of 5000 * 1.977408384e-08 = 9.88704192e-05.

For mortality, we could say the expected loss this year for our 5k driver who is 30 years old is ~50 years at the usual \$50k/QALY, without discounting, would be 5000 * 3.431544214e-09 * (50 * 50000) = \$42. That's just the first year, while 30yo, and each year the loss shrinks since you get closer to death; a quick hack to sum the series to get a total expected loss with discounting at the usual 3%:

R> sum(sapply(seq((80-30), 0), function(t) { 5000 * 3.431544214e-09 * t * 0.97^t * 1.0 * 50000 }))
# [1] 420.5466717

Injuries is more difficult. Browsing through a few papers on TBI and QALYs, I find QALY/life-expectancy losses from TBI in juveniles: "Measuring the Cost-Effectiveness of Technologic Change in the Treatment of Pediatric Traumatic Brain Injury", Tilford 2007 The estimates are kind of shocking - TBI is a very serious problem. (Not too surprising after looking at "Quality of Life After Traumatic Brain Injury: A Review of Research Approaches and Findings" and some of the citations in "Is aggressive treatment of traumatic brain injury cost-effective?" Whitmore et al 2012, or when I remember that a lot of military veteran dysfunctionality is probably due to TBI.)

Preference-weighted health outcomes in children who survived a TBI hospitalization were reported from a cohort of children admitted to 10 pediatric intensive care units (PICUs) that were located nationally. Subject inclusion criteria followed the inclusion criteria for estimating survival probabilities and required that the child be less than 18 years of age and admitted to the PICU with a Centers for Disease Control and Prevention-defined TBI^13^ that required either endotracheal intubation or mechanical ventilation. An initial description of these outcomes and construct validity has been reported elsewhere.^9^ Scores ranged from 0.09 to 1.00 at 3 and 6 months after discharge from the ICU, but mean scores increased from 0.51 to 0.58 between the two periods...Recent work on life expectancies after TBI suggests that life expectancy will differ significantly depending on the functional outcome of the patient after hospital discharge.^20,21^ Patients with moderate disabilities were found to have a 4-year reduction in life expectancy, whereas patients rated as extremely severe were found to have a life expectancy only 50% of the population average.^22^ A study of children and adolescents after TBI also found substantial reductions in life expectancy when severe functional limitations were present.^23^ For a child aged 15 years, life expectancy was an additional 14.9 years if the child was not mobile, 34.2 years if the child had poor mobility, and 54.8 years if mobility was fair or good...Hospital charges for pediatric TBI patients increased to a maximum of \$19,000 and then fell to approximately \$13,000...On average, children who required an ICP monitor used approximately \$18,600 worth of services in the immediate period after discharge. Service costs decreased by approximately 50% between the 3-month follow-up interview and the 6-month follow-up interview. Assuming that service use declines linearly over time, the average cost per patient is approximately \$35,750 in the first year after discharge from the PICU.

Whitmore et al 2012 reports similar QALY estimates for adults; for example, QALY drops from 1 at #5 (healthy) to 0.63 at #4 on the Glasgow Coma Scale (concussion-like: "Opens eyes spontaneously / Confused, disoriented / Flexion/withdrawal to painful stimuli"), and 0.26 at #3. Details on estimates:

Life expectancy for Glasgow Outcome Scale (GOS) score categories 4 and 5 were obtained from 2001 US vital statistics.^2^ We assumed a GOS status of 4 had no adverse effect on life expectancy. Diminished longevities associated with GOS scores of 3 or 2 were calculated according to formulas derived from survival studies of these patients' mortality rates.^4,10,11,13^ Appendix Table 1 shows the expected years of life for each of the 4 age categories studied. Aoki and associates1 elicited utilities of different GOS states from 140 medical professionals, using the routine gamble approach. Their results are shown in Appendix Table 2. Quality-adjusted life years (QALYs)—and costs—are discounted at 3% per year of life. It is assumed that future rewards and costs are valued less than immediate ones, and routine practice is to discount them at 3% or 5% per year.^8^ As an example, a 20-year-old can expect to live, on average, 58^12^ years. If he or she remains in perfect health (utility = 1), that translates to 28.21 QALYs, with discounting. Appendix Table 3 illustrates the number of expected QALYs associated with a given age and GOS score.

So Whitmore et al 2012 finds that a healthy 20 year old's expected (discounted) QALYs of 28.21 drops to 17.77 if he is hit hard enough to trigger a #4, which at \$50k again is a huge lifetime loss of \$522,000. For the 40yo, the same calculation is \$436,500. Splitting the difference gives me a \$479,250. The losses get worse with more severe Glasgow Coma Scales, where #1 effectively equals death. Since I'm not sure how TBIs break down by Glasgow rating, I can't do an overall expected value but whatever it is, it must be >\$479,250 since that was the least damaging scenario Whitmore considered. So the expected loss from a TBI injury but not death is \$479k (ignoring the immediate medical costs since those will generally be paid by other people like insurers or the government); now we again need to compute the probability of a TBI injury each year and sum the series:

R> sum(sapply(seq((80-30), 0), function(t) { 5000 * 3.431544214e-09 * t * 0.97^t * 0.63 * 50000 }))
# [1] 264.9444032

So a quick estimate of the net present expected loss caused by TBI death or injury while in a car over a lifetime for a 30yo is -\$685. Or to put it the other way, we should be willing to pay up to \$685 to reduce our car TBI risk to zero.

comment by gwern · 2016-01-17T02:44:37.467Z · score: 10 (5 votes) · LW(p) · GW(p)

How much do these helmets reduce risk and how much do they cost to buy & use? That's tricky to answer, but maybe some bounds will be helpful.

\$685 in present value is roughly equivalent to \$27 spent each year over the next 50 years, discounting at 3% (sum(sapply(1:50, function(t) { 27 * 0.97^t }))). So even something which reduced your car TBI risk to zero would not be worth paying more than \$27 each year for the rest of your life. The mentioned helmets all sound like they only reduce acceleration or energy somewhat, and Crasche is quoted by Dorikka as estimating a 25% reduction in impact (which translates to an unknown reduction in TBI risk); another quote claims seatbelts reduce death/injury by ~50%. Let's be extremely optimistic and go with the latter, that our TBI risk falls by 50% using a Crasche helmet. Then the gain from a Crasche helmet is 685 * 0.5 = \$342.

The cost of the Crasche helmet is ~\$30, leaving \$312. Let's assume there's never any replacements and we just need to consider the annual hassle of wearing it. Working backwards again, that leaves room for an annual cost of no more than ~\$12.3, which is small. I drive maybe thrice a week, so the per-trip cost of use needs to be <12.3 / (52*3) or <\$0.07. Alternatively, if we don't think the Crasche helmet is remotely sufficient, a much better helmet might cost more like \$100 up front, leaving \$242, leaving \$9.5 for annual expenses, or <\$0.06.

Personally, while I don't mind driving with a helmet as much as \$1 an hour (and so extremely high annually) like some people claim, I think I would mind a nickel's worth each trip, which defeats Crasche even with extremely optimistic assumptions on efficacy. If we wanted to make Crasche cost-effective, we could argue that \$100k/year is a better value, which will double estimates of benefit; or we could try to expand our sources of harm to include TBIs from other sources like falls (although that would also increase the cost of usage: it's one thing to only need to wear it in your car where no one will see, another thing to walk around routinely wearing it); or we could deny discounting, which increases the loss considerably and helps overcome the fixed present cost of buying the helmet. But to be fair, we'd also want to reduce the efficacy of Crasche to much less than 50%, take into account that we're wearing seat belts while a large fraction of TBI cases likely were not, consider the advent of self-driving cars in the next 15 years reducing human error rates, and overall, I'm not seeing much that looks like it could make a driving helmet the sort of slamdunk case that one can make for, say, vitamin D. As far as car safety goes, a helmet feels like it's going to be inferior to stuff like getting a dashcam, upgrading to an electric car with its bigger crumple zones & higher mechanical reliability (I understand the Tesla cars may be the safest ones on the market right now), saving up for self-driving cars, making a habit of reinflating tires more regularly, taking a defensive driving class, etc - to say nothing of much larger risks like falling getting out of the shower. (I installed some anti-slip treads after I did just that; feels like money well-spent every time I step out.)

The same also applies to walking helmets: falls are highly concentrated in the elderly and very young (while car TBIs are more evenly distributed) and you would need to wear a helmet almost 24/7 once you've guarded against ice and shower falls (increasing costs much more over car TBIs). So race-car drivers, football players*, people at much higher than usual risks? Probably, maybe. Regular people? Not really.

* although I would say after reading through all the football studies and these TBI studies, I would not, hypothetically, let my children ever play contact football and especially not highschool football. If they want to play sports, there must be safer ones they could try. Like BASE jumping.

comment by gwern · 2016-08-24T00:47:20.631Z · score: 1 (1 votes) · LW(p) · GW(p)

"Long-Term Outcomes Associated with Traumatic Brain Injury in Childhood and Adolescence: A Nationwide Swedish Cohort Study of a Wide Range of Medical and Social Outcomes", Sariaslan et al 2016, is a population registry study which reports within-family correlations adjust for education about various negative outcomes with 1 or more diagnosed TBIs representing 9.1% of the population (their twin sample was too small); within-family studies control for tons of the usual confounders (and indeed the correlations are smaller than if you had used the general population) and are probably close to the causal effect (possibly underestimating it since so many TBIs go unreported).

TBI is common enough that the effects are large on a population-wide basis:

We found that the crude population contributions of TBI explained approximately...2%–6% of the population differences in the outcomes. The strongest population attributable risks were found for the severe outcomes, including psychiatric inpatient hospitalisation (PAF = 5.5%; 4.9%–6.1%), premature mortality (PAF = 4.7%; 2.9%–6.5%), and disability pension (PAF = 4.6%; 3.8%–5.3%).

Interestingly, the effects of TBI get worse with age: the youngest age bracket (despite having lots of falls) has the smallest RRs while they increase especially for adolescents. (This was the opposite of what I expected.)

They find RRs of:

  1. disability pension: 1.49

    • Population rate: 3.9%
    • Lifetime cost: Sariaslan gives a quick opportunity cost estimate of "US$1.3 million per person" from the inability to work & earn a normal income over the next 30 years
  2. Psychiatric visit: 1.31

    • Population: 14.2%
    • Lifetime cost: ?
  3. Psychiatric hospitalization: 1.57

    • Population: 5.7%
    • Lifetime cost: ?
  4. Premature mortality (death age <41): 1.40

    • Population: 0.8%
    • Lifetime cost: tricky since it's not quite a RR on all-cause mortality: the age 41 is when they stopped following individuals in their sample. If we assume that the mortality RR remained indefinitely, then using my Gompertz curve functions, a RR of 1.40 for a 30yo would represent a loss of 3.09 years over the next ~50 years, for a 10yo a loss of 3.147 years over the next ~70 years etc. So ignoring discounting, ~\$150k from the mortality alone.
  5. Highschool dropout: 1.28

    • Population: 8.9%
    • Lifetime cost: somewhere upwards of $250k in the USA, estimates as high as $1m.
  6. On means-tested welfare benefits: 1.19

    • Population: 11.5%
    • Lifetime cost: Sweden is famous for spending a lot on welfare, but the welfare & public spending are quite diverse, this doesn't specify how long each individual is on welfare or whether it's household or individuals. http://ec.europa.eu/social/BlobServlet?docId=9044&langId=en suggests that a prevalence of 11.5% must refer to household welfare, and estimates that in 2008 the average number of months (from 1990 to 2008) was 6.1 months at 43987 SEK per month or \$5.2k or \$31.72k total on average.

So the undiscounted cost of 1 nonfatal TBI for a 10yo (why 10yo? so they have time to drop out of highschool) in Swedish America would be something like:

(0.039*1.49 -0.039)*1300000 + ? + ? (0.008*1.40 - 0.008)*3.147*50000 + (0.089*1.28 - 0.089)*250000 + (0.115*1.19 - 0.115)*31720 = >\$32,269

For the 30yo

(0.039*1.49 -0.039)*1300000 + ? + ? (0.008*1.40 - 0.008)*3.09*50000 + (0.115*1.19 - 0.115)*31720 = >\$26,030.482

Unfortunately, hard to see how to do much about this. The top category of TBI is normals falls, cars, then assaults, then miscellaneous: https://www.cdc.gov/traumaticbraininjury/pdf/blue_book.docx

An estimated average of 595,095 are fall-related TBIs, 292,202 motor vehicle traffic TBIs, 279,882 struck by or against events, and 169,625 assault-related TBIs occurred annually....Struck by or struck against events are those in which a person was struck unintentionally by another person or an object, such as falling debris or a ball in sports, or that someone struck against an object, such as a wall or another person. For this report, only unintentional and undetermined struck by or struck against events were included. Struck by or struck against events related to assaults (for example, being struck by a fist) are in the assault category. Struck by or struck against events were only reported for all ages because small sample sizes precluded reporting them for all three data sources (NHAMCS, NHDS and NVSS)

For 30yos, cars are 40% of TBIs, falls are 2.7% of TBIs, assault is 19% of TBIs, struck by by or against is 0.7%, and the ominous 'other' is 37%. So while we can probably ignore the 'assault' due simply to demographics (I suspect most readers here have low risk of crime), and car travel represents a fairly focused area of intervention, the 'other' can't be fixed except by always wearing a helmet, which would be difficult if only for social reasons.

comment by pepe_prime · 2016-08-25T19:21:22.350Z · score: 0 (0 votes) · LW(p) · GW(p)

For injuries

R> sum(sapply(seq((80-30), 0), function(t) { 5000 * 3.431544214e-09 * t * 0.97^t * 0.63 * 50000 }))
# [1] 264.9444032

Rate should be 1.634253963e-08, yielding about $1261.78 lifetime loss.

comment by adamzerner · 2016-06-30T00:20:49.277Z · score: 0 (0 votes) · LW(p) · GW(p)

The analysis uses $50k for a QALY. The analysis also assumes a normal lifespan of 80 years.

My impression is that LW readers are likely to place much higher values on their life, and to have longer expected lifespans. I could see LW readers having QALY's of 2-5 times the $50k figure. And I could see LW readers (ex. signed up for cryonics) having much longer expected lifespans.

So I could see that for many readers here, the downside should be multiplied by, perhaps an order of magnitude.

comment by adamzerner · 2016-06-29T23:46:47.942Z · score: 0 (0 votes) · LW(p) · GW(p)

Thank you so much for this analysis!

comment by James_Miller · 2015-07-31T15:54:29.373Z · score: 2 (2 votes) · LW(p) · GW(p)

Something like being hit by a car? Pedestrians (70-80K deaths & injuries per year) and cyclists (~50K deaths and injuries per year) are very likely to get TBI in an accident.

Excellent point.

Still, having lightweight protection for your brain that doesn't reduce visibility seems like it would have a big net positive impact, but I might be wrong.

comment by [deleted] · 2015-08-01T18:15:07.448Z · score: 4 (4 votes) · LW(p) · GW(p)

From the CDC:

Most drivers and passengers killed in crashes are unrestrained. 53% of drivers and passengers killed in car crashes in 2009 were not wearing restraints.

Seat belts dramatically reduce risk of death and serious injury. Among drivers and front-seat passengers, seat belts reduce the risk of death by 45%, and cut the risk of serious injury by 50%.

Seat belts prevent drivers and passengers from being ejected during a crash. People not wearing a seat belt are 30 times more likely to be ejected from a vehicle during a crash. More than 3 out of 4 people who are ejected during a fatal crash die from their injuries.

I bet a lot of TBI is due to being ejected from the vehicle.

comment by Houshalter · 2015-08-02T02:48:20.311Z · score: 2 (2 votes) · LW(p) · GW(p)

But what about the 47% who die who are wearing seat belts? Is that number even different than the base rate of people who wear seat belts?

comment by [deleted] · 2015-08-02T15:02:53.966Z · score: 0 (0 votes) · LW(p) · GW(p)

Well, to use the numbers given, if P(death) when you don't wear a seatbelt equals 1 and P(death) when you do equals 0.55, and 53 people die not wearing a seatbelt and 47 die wearing one, then 1 x A1 = 53 and 0.55 x A2 = 47. A1=53 and A2=85.45. A2/(A1+A2) = 0.617. So 62% of people are wearing a seatbelt at any given time.

I'm assuming they're calcing the two figures given the same methods which is not a given. They might be using real world figures for the former statistics and car crash simulator numbers for the latter statistics which would make more sense but throw my calculation off. 62% seems low to me.

comment by Houshalter · 2015-08-03T06:12:58.472Z · score: 0 (0 votes) · LW(p) · GW(p)

I am certain that the P(death|~seat belt) != 1.

comment by [deleted] · 2015-08-03T06:43:05.306Z · score: 1 (1 votes) · LW(p) · GW(p)

That's irrelevant. As long as the ratio of seatbelt to not seatbelt is 55/100, you'll end up with the same answer. ~seatbelt could be 0.1 or 0.03 or 0.00007.

comment by RichardKennaway · 2015-07-31T15:31:52.491Z · score: 0 (0 votes) · LW(p) · GW(p)

Something is causing a huge number of Americans to " receive a motor vehicle induced traumatic brain injury every year."

Do Americans wear seatbelts much? Especially by passengers.

comment by Dagon · 2015-07-31T16:40:49.951Z · score: 2 (2 votes) · LW(p) · GW(p)

Most US states mandate seatbelt usage. Compliance, of course, varies.

I'd argue that the group of drivers and passengers who are seriously considering wearing a helmet in the car are nearly 100% likely to wear a seatbelt whenever available, and are probably the type who prefer safer (more airbags, better crash ratings) cars.

comment by James_Miller · 2015-07-31T15:36:43.506Z · score: 0 (0 votes) · LW(p) · GW(p)

A lot of us don't, but airbags are mandatory.

comment by Dorikka · 2015-07-31T05:38:47.570Z · score: 11 (11 votes) · LW(p) · GW(p)

I've looked up a few studies over the past few months in an attempt to understand direct causes of TBI and what kind of accelerations are "safe" - those under which a TBI (or diffuse axonal injury, DAI) is unlikely to occur, and to get a sense of what types of activities different accelerations correspond to. I'm dumping some info below without many citations as it's much lower effort than the alternative. If there's anything in particular that one is interested in, I may be able to find the relevant article. if you see anything that is wrong, please let me know.

  • TBIs appear to be caused by a combination of linear and rotational acceleration; these appear to cause injury via different mechanisms. Linear force/acceleration appears to create a high-pressure volume on the side of impact and a low-pressure volume on the opposite side of the head, with injuries possibly resulting from either. Rotational acceleration can, broadly speaking, cause brain tissues to stretch and twist in a way that they're not resilient to. However, this only appears to cause direct damage in the most severe of cases. In most cases, the majority of damage appears to be caused by a chemical cascade initially triggered by the damaged tissues. Bleeding of the brain is also possible, though I am not very clear on the causes of this.Regarding the chemical cascade, calcium ions spring to mind as one of the damaging species - curiously, repeatedly recovering from chronic alcohol abuse seems to be contraindicated also due cumulative damage from increased release of calcium ions, and they also may be rather indirectly linked to Alzheimers. More detail on the impacts and causes of calcium ion release in the brain is on my to-learn list.

  • In severe cases, it appears that hospitals sometimes administer treatment to control intracranial pressure or manage the chemical cascade to reduce damage. (I am not sure whether the focus is on inhibiting the cellular mechanism perpetuating the cascade or neutralizing the offending species themselves.)

  • Concussions seem to start happening around linear accelerations of ~50g (though one article places this at around 20-30g if I remember correctly, and expresses concern regarding repeated impacts as low as 10g) and/or a rotational acceleration of ~2000 rad/sec^2. Impact durations appear to range from ~3 milliseconds (against a hard surface) to 8 milliseconds (wearing a football helmet). As expected, lateral impacts (from sides, or front/back of head) produce greater rotational acceleration compared to impacts to the top of head. I would personally expect that injuries involving cessation of motion of the head would be hazardous at much lower peak velocities than those involving an object striking the head, as the 1) head is (usually) more massive than the object striking it, resulting in greater net force and 2) neck strength may reduce peak accelerations in the latter case, but perhaps not the former.

  • These links give examples of accelerations that appear to be produced during assorted daily activities. An experiment was done in which people of various ages shook their heads up/down in an "unconstrained manner", resulting in peak linear accelerations of ~4-5g and peak rotational accelerations of ~250-500 rad/sec^2. This appears to be somewhat difficult to reconcile with reports of injuries from headbanging, as these accelerations are very much below typically expressed hazardous levels.This article seems to refer to a similar motion, while reaching radically different results regarding accelerations (though, as far as I tell, it only does modeling, no measurement of actual head movement.)

comment by Lumifer · 2015-07-31T14:39:15.896Z · score: 0 (0 votes) · LW(p) · GW(p)

Weren't there a lot of studies about frequent low-intensity shocks to the head -- specifically in the context of American football (and boxing before that)?

comment by Username · 2015-08-08T17:36:09.338Z · score: 2 (2 votes) · LW(p) · GW(p)

I did my undergrad engineering capstone project at the beginning of this year creating a linear accelerator to subject networks of mouse brain cells to repeated 50g acceleration loads, based specifically off of football helmet impact data.

I was only assisting the PI running the research so I hadn't read all of the literature, but from what I know the jury is out on a good model of risk from repeated head impacts. We can tell you pretty well what the risk is for single impact events, but expect a few years for the first characterization of repeated trauma to be published. This is based on my lab's timing of course - I'm not sure how far along other labs are with this.

comment by Dorikka · 2015-08-06T03:41:19.222Z · score: 0 (0 votes) · LW(p) · GW(p)

Most of the studies that I've seen either seem to be looking at high-acceleration impacts or are trying to quantify impacts received in "daily life". I have repeated impacts flagged in my head as "result unknown" - I haven't come across anything that I can remember that would give legit thresholds for how hard a repeated impact has to be before it would cause damage (other than the 10g figure noted above). People seem to agree that repeated impacts have the capacity for great harm, and I remember seeing that people with a certain gene appeared to be more prone to symptoms if subjected to repeated impacts, but that's pretty much all I remember. Let me know if you find anything.

comment by Dorikka · 2015-08-07T03:24:46.785Z · score: 10 (10 votes) · LW(p) · GW(p)

I sent the Crasche folks an email asking for data documenting the performance of their product. I received the following results as part of a brochure:

LACROSSE CROSS-IMPACT TEST RESULTS (these appear to be stick-to-head):

Sample # Impact Location Cross Velocity (MPH) Severity Index Peak G

Bare Headform Side 38.19 1051 188

Size Small Side 39.94 68 49

Size Large Side 38.64 8 24

LACROSSE BALL IMPACT TEST RESULTS (these appear to be ball-to-head):

Sample # Impact Location Ball Velocity (MPH) Severity Index Peak G

Crosse BXX 1 68.34 278 179

Crosse BXX 2 69.3 208 146

Crosse BXX 3 70.75 294 186

The following sentence was also included in the reply: "Note - these tests are for impact coming onto the head. In a drop test, which simulates a head on collision, a 9 mph event showed an impact reduction of about 25 %."

For reference, I remember reading somewhere that football helmets tend to increase impact duration from about 3 ms to about 8 ms. Assuming uniform force distribution over the duration of the impact, this amounts to ~60% reduction in peak acceleration (over whatever force domain that acceleration is correct for.) Crasche seems to guard effectively against forces similar to that of a lacrosse stick being swung at the head. Unfortunately, the results of the second test don't really tell much about the usefulness of the hat, as the Crasche folks seemed to be satisfied with concluding that it's effective based on seeing a Severity Index (I assume this is based on the head injury criterion?) <300 when taking a lacrosse ball to the head, despite the huge accelerations.

Regarding the drop test - 9 mph gives around 137-82g of acceleration against a hard surface, assuming impact duration of 3-5ms. So we're looking at 6700-4000N (human head weighs around 5kg). In this domain, we can compare the 25% advertised reduction against the ~60% ballparked estimate for force reduction due to a football helmet.

In summary, the performance appears to be inferior (in terms of pure linear acceleration reduction) to a sports helmet, as one would expect. The hat appears to be more effective against object-to-head impacts (involving smaller forces) relative to impacts that result in the head being brought to a halt from motion (involving larger forces) - perhaps the crushable elements providing the resistance are crushed by the larger forces? My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won't do much of anything as the crushable bits are crushed too fast to be effective.

comment by James_Miller · 2015-08-07T04:03:49.909Z · score: 1 (1 votes) · LW(p) · GW(p)

Thanks for researching this.

comment by G0W51 · 2015-09-25T20:20:21.222Z · score: 0 (0 votes) · LW(p) · GW(p)

My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won't do much of anything as the crushable bits are crushed too fast to be effective.

I don't see how the latter clause follows from the former. You said that in the drop test, the impact reduction was roughly 25%. This isn't huge, but I can't say it "won't do much of anything." Were you thinking of something else to support your claim?

comment by Dorikka · 2015-09-26T16:13:32.804Z · score: 0 (0 votes) · LW(p) · GW(p)

No other source, but keep in mind that helmets are tuned for a certain force level. Too durable and helmet does not reduce peak force as it does not crush. Too weak and it crushes quickly, again with little reduction in peak force. This should just empasize to use the 25% number here though since the forces are more representative.

Redacting "won't do much of anything" except as implied by 25%, but keep in mind that if peak accelerations are much higher than the given case, the helmet will be less effective due to the above. This may or may not be the case in car crashes depending on speed.

comment by G0W51 · 2015-09-23T21:25:04.633Z · score: 0 (0 votes) · LW(p) · GW(p)

Severity Index (I assume this is based on the head injury criterion?)

Actually, in an email they said the head of NOCSAE did the test, so presumably the NOCSAE Severity Index was used. An NOCSAE article says, "There is no measurable difference in safety of helmets with scores below the 1200 SI threshold." So in other words, in the test the hats did not protect against any significant damage, because no significant damage was done even without the hat. Despite this, the webpage said said that, "The Crasche hat reduces the severity of blunt force impact by 94%." I count this deceptive marketing as a strike against the product.

That said, given the low cost of purchasing and wearing the hat, it seems worthwhile for a transhumanist to purchase, simply due the vast gains to be had from a slight reduction in risk of death.

comment by Dorikka · 2015-09-26T15:58:48.827Z · score: 1 (1 votes) · LW(p) · GW(p)

Interesting - thanks for checking this. If the Severity Index is claiming no significant damage below 1200, I think it may be incorrect or may have a different criterion for severe damage. Some helmet standards seem to be fairly insensitive, only accounting for moderate or severe brain injury whereas MTBI can have long lasting effects. Yes, I discount Severity claims as the metric does not appear to give reasonable results. 188g is a crapload of linear acceleration, but metric puts it under threshold...I dont buy it, so am left to judge on peak linear accel instead (shame that rotational accel was not measured...)

comment by G0W51 · 2015-09-21T03:54:23.900Z · score: 0 (0 votes) · LW(p) · GW(p)

My gut says that the performance in a vehicle collision will probably bring the head to a halt...

Presumably, the impact would cause the pedestrian to fly back in roughly the same direction the car was moving during the impact, rather than come to a complete stop. That said, I don't really know enough about the tests to know if this would make a difference in efficacy. Could you link the exact data you received?

comment by Dorikka · 2015-09-21T11:29:00.249Z · score: 0 (0 votes) · LW(p) · GW(p)

The data is posted above, unlikely to get around to Dropboxing it so I can link (as it was from an email). I agree with you re body movement in a vehicle collision. However, at some point your body would stop. If your head hit something while your body was in motion, thr impacted object would likely have enough strength to bring the head to an abrupt halt. (Contrast with a knife being punched through paper mache - I would expect the force on the lnofe to be much lower than if hitting concrete, as it would go through the paper mache without much velocity change.)

comment by btrettel · 2015-07-30T23:58:40.794Z · score: 10 (10 votes) · LW(p) · GW(p)

Good suggestion. I'm a cyclist and sometimes I walk around wearing my bike helmet. Some people give me funny looks, but I don't care. To regularly wear helmets, you have to recognize that avoiding TBI is more important than looking slightly silly or messing up your hair. Unfortunately most people don't get this. I think if helmets become more popular people will find that they don't actually mind the look, as you suggested in another comment.

Risk compensation is one potential problem with wearing a helmet. An example was mentioned in the original post: drivers passing cyclists who wear helmets closer. Also concerning is that cyclists ride more dangerously if they wear helmets (here's an article which I haven't read in full, but it discusses this issue). I imagine seat belts have a similar effect, as might drivers wearing helmets. Based on this idea backwards, I've read a proposal to add a spike to steering wheels to reduce dangerous driving.

Also worth noting is that avoiding long commutes and drives improves safety. Risk (probably) increases monotonically with duration.

One last suggestion would be to drive with a dashcam to make yourself slightly safer. I ride my bike with a very obvious helmet cam and I have observed that some drivers seem to drive safer around me when they notice it. I'm recording them, so if they make a bad move they'll be much worse off in court. I also think the camera makes me ride safer for the same reasons.

comment by James_Miller · 2015-07-31T02:44:37.353Z · score: 4 (4 votes) · LW(p) · GW(p)

I ride my bike with a very obvious helmet cam and I have observed that some drivers seem to drive safer around me

This is a great safety hack.

You have given me an idea for a research paper (which I will never do). You get two types of helmet cams, one that looks like a helmet cam, and one that doesn't. But if someone else puts the helmet cam on you, you can't tell which it is although anyone looking at you could. You then randomly assign which bicyclists wear which type of helmet cam and test how the type of cam effects nearby drivers.

comment by Gurkenglas · 2015-07-31T19:22:04.206Z · score: 4 (4 votes) · LW(p) · GW(p)

This could only disprove or fail to disprove the absence of any noticeable effect on other drivers, since them behaving differently might make you behave differently, by, say, subconsciously inferring from their behavior that you are in the helmet-wearing group.

comment by James_Miller · 2015-07-31T20:22:03.114Z · score: 1 (1 votes) · LW(p) · GW(p)

Good point.

comment by ChristianKl · 2015-08-03T09:13:14.003Z · score: 1 (1 votes) · LW(p) · GW(p)

A key question might be: How hard is it to convince a company who already manufactures helmets with visible cams to run such a study?

comment by isionous · 2015-08-08T08:00:11.965Z · score: 3 (3 votes) · LW(p) · GW(p)

Risk compensation is one potential problem with wearing a helmet... I imagine seat belts have a similar effect, as might drivers wearing helmets. Based on this idea backwards, I've read a proposal to add a spike to steering wheels to reduce dangerous driving.

I recommend watching car crash compilations. They definitely help you feel the risk of driving on an emotional level. I feel I've learned some things that improve my driving safety, but probably the biggest safety gain is I just tend to drive more cautiously due to car collisions being very present in my mind.

comment by btrettel · 2015-08-08T14:05:48.058Z · score: 1 (1 votes) · LW(p) · GW(p)

Great suggestion. I've watched a fair number of these, along with bike crash videos. The mental simulation value is fairly high, because you won't be in every situation on the road, and you should have some idea about what happens if you take certain actions.

comment by jefftk (jkaufman) · 2015-07-31T17:13:20.662Z · score: 6 (6 votes) · LW(p) · GW(p)

When I looked into this a few years ago I turned up Prevention of Head Injuries to Car Occupants: An Investigation of Interior Padding Options (McLean et. al. 1997). The improvement in interior padding and airbags since 1997 is probably enough to bring the benefit of a bicycle-style helmet down to just a few percent injury reduction.

But even assuming its as high as 10%, Nick Beckstead wrote:

You allegedly get 1 micromort from driving 230 miles. Say that takes 4 hours, and say you get to reduce 10% of that by wearing the helmet. Then wearing a helmet for 1 hr saves your life with probability 1 in 40 million. So the question is whether you prefer a 1 in 40 million chance of saving your life or the convenience of not wearing a helmet in the car for an hour.

If you valued your life at $40M, then the question would reduce to whether you would be willing to wear a helmet for an hour if it saved you a dollar (neglecting safety benefits). I wouldn't wear a helmet for an hour for a dollar, and would pay a dollar to avoid wearing the helmet. Since all these estimates are average or conservative, that suggests it is not worth it to wear a helmet (at least for me).

comment by gwern · 2015-07-31T20:13:22.603Z · score: 12 (12 votes) · LW(p) · GW(p)

I don't believe Nick's introspection here. $1/hour may sound plausible considered as a single choice for 1 hour, but not repeated, as it would be, over a lifetime: if you spend 3 hours a day in a car (which I have for a large period of my life), then he's willing to pay 3 * 365 = $1.1k a year or easily $50k over a lifetime to not wear a helmet? To put this in further perspective, the median American household's income is around that; so by claiming $1/hr, he is implicitly claiming other things like 'if a law were passed mandating wearing a helmet, I and my household would gladly labor like a slave for a year in exchange for an exemption', and so on and so forth. (You can quibble about things like discounting and Nick's probable above-median income and how many hours he actually spends in a car but still - $1/hr is actually quite a bit!)

Further, realistically, habituation and the hedonic treadmill means he would very quickly get used to it as a habit and eventually even come to expect it - like people get used to yarmulkes or old-timey men felt naked without their hats or the deaf/hearing-impaired get so used to their hearing-aids that they forget they are wearing them or how orthodontic patients can survive even the notorious and extremely unpleasant 'head gear'. Or more pertinently, they have already adapted quite nicely to car safety devices far more intrusive, restrictive, and unpleasant than a lightweight helmet: three-point seatbelts.

I am sure Nick really does dislike wearing a helmet to some degree (at least during the adaptation period...), but -$1/hr? No.

comment by gwern · 2018-11-19T01:29:33.762Z · score: 3 (1 votes) · LW(p) · GW(p)

Galaxy brain take: one man's modus ponens is another man's modus tollens - he wouldn't wear a car helmet, so by the same logic, it's not worthwhile to wear a helmet while biking: https://www.forbes.com/sites/carltonreid/2018/10/21/i-do-not-wear-a-bicycle-helmet/

comment by jefftk (jkaufman) · 2015-08-07T19:21:29.235Z · score: 2 (2 votes) · LW(p) · GW(p)

if you spend 3 hours a day in a car

That's a lot more than most people do. Conservatively assuming that all travel is via car, the 2014 average on the American Time Use Survey [1] is 1.11hr/day [2]. At $1 = 1hr, that's $1.11/day.

But I do agree habituation is significant here. People probably felt similarly about seatbelts but I don't notice mine.

[1] http://www.bls.gov/tus/tables/a1_2014.pdf

[2] Broken down as, in hours per day: 0.02 for personal care, 0.10 for eating and drinking, 0.04 for household activities, 0.27 for purchasing goods and services, 0.08 for caring for and helping household members, 0.05 for non-household members, 0.27 for work, 0.03 for education, 0.04 for organizational, religious, and civic activities, 0.21 for leisure and sports.

comment by [deleted] · 2015-08-01T18:48:25.393Z · score: 0 (2 votes) · LW(p) · GW(p)

$50k a year times 40 years equals $2 million. He's maybe overestimating the price he's willing to pay, but he's also overestimating how much people typically value their lives at. You're also using a really high estimate for number of hours in the car. 3 x 365 x 60 = 32,850 miles per year.

comment by gwern · 2015-08-01T20:00:59.606Z · score: 3 (3 votes) · LW(p) · GW(p)

I did not say $50k a year, I said $50k over a lifetime ($1.1k times around 40-50ish years, since you spend many of the early ones strapped in and driving tends to decline in old age; and honestly I don't want to project out past 2060 as it is).

You're also using a really high estimate for number of hours in the car. 3 x 365 x 60 = 32,850 miles per year.

I don't think that is extreme. As I said, I commuted that much for 4 years, and my dad spent most of his career with a 2h+ commute just for work, never mind all the other driving entailed in suburban life. Americans drive a lot.

comment by [deleted] · 2015-08-01T20:20:33.375Z · score: 2 (2 votes) · LW(p) · GW(p)

No, $2 million is median household lifetime earnings if they work for a typical 40 years which is way below the $40 million he's estimating.

Also, you just named two examples of outliers and suggested they were representative of your entire experience. Just glancing at estimates, most are between 10000 and 15000 miles per year as typical for Americans. Europeans are probably lower.

Also, Nick overestimated average driving speed which means he's even further overestimating the cost of not wearing a helmet. I calced it at around $50 per year; $.20 per hour.

comment by jefftk (jkaufman) · 2015-08-07T19:09:35.171Z · score: 2 (2 votes) · LW(p) · GW(p)

3 x 365 x 60 = 32,850 miles per year.

Why are you assuming an average speed of 60mph? Most people's commutes have a lot more traffic than that.

Also, 336560 is 65,700 not 32,850.

The average person spends something like 1hr/day in a car, and travels an average of 13476 miles/year which gives us more like 36 mph.

comment by [deleted] · 2015-08-07T19:56:03.258Z · score: 0 (0 votes) · LW(p) · GW(p)

The original estimate which gwern based his analysis on used a speed of about 60 mph, which is necessary to use when reversing the calculation back into miles. I would agree average speeds are probably lower.

Edit: I just noticed my calculation was wrong. I'm not sure where I got 32850 from. It's more like 60 something thousand. Whoops.

comment by jefftk (jkaufman) · 2015-08-09T14:18:29.144Z · score: 0 (0 votes) · LW(p) · GW(p)

Sorry, I'm not seeing where gwern uses 60mph?

comment by [deleted] · 2015-08-09T16:00:47.865Z · score: 0 (0 votes) · LW(p) · GW(p)

He's making a calculation using hours based on an analysis originally written in micromorts per mile. He has to convert from miles to hours to do that. He uses the estimate you gave him which assumed 57.5 mph to be exact to make that conversion. I used 60 as a rough approximation. To calculate the miles he's using for his analysis, I have to use the same estimate. It's an unstated assumption gwern makes to get to $50k in a lifetime. A lower average speed would make Nick's argument stronger and gwern's cost estimate lower.

comment by ChristianKl · 2015-08-03T08:58:01.919Z · score: 0 (0 votes) · LW(p) · GW(p)

You care for more than just mircomorts. You also care for not getting brain damage.

comment by gjm · 2015-08-03T12:36:33.796Z · score: 1 (3 votes) · LW(p) · GW(p)

You can measure that in micromorts too, via QALYs.

comment by adamzerner · 2015-07-30T22:59:01.953Z · score: 5 (5 votes) · LW(p) · GW(p)

1) I get the impression that most people do most of their driving alone. And of the people in the car with you, it's mostly pretty close friends/family, whom you presumably are pretty comfortable around. As for random people seeing you through the window, I wouldn't think that that'd be too embarrassing, given that it's so fleeting and that you'll never see them again. So all in all, I don't see that there's too big a downside. Maybe it's just because it leads to the self-narrative of "I'm a weirdo"?

I happen to take great joy in being contrarian in rational ways haha. So if I drove I'd totally do this!

2) Different way of looking at it (for parents) - would you chose to put a helmet on your child?

comment by James_Miller · 2015-07-30T23:18:53.955Z · score: 0 (0 votes) · LW(p) · GW(p)

(2) Below a certain age, yes (now at least) if I thought it added much safety value beyond a child's seat. Above this age, his choice but I would offered to pay for it.

comment by Lumifer · 2015-07-30T17:51:58.598Z · score: 5 (5 votes) · LW(p) · GW(p)

The numbers of traumatic brain injury (TBI) cases caused by falls are of about the same magnitude as TBI caused by motor vehicle accidents (CDC data, the relative frequency depends on age).

Would you recommend putting on a helmet as soon as you get out of bed in the morning for people in their 40s and older?

comment by James_Miller · 2015-07-30T18:12:53.945Z · score: 9 (9 votes) · LW(p) · GW(p)

Per unit of time, I suspect you are much more likely to get a TBI while in a car than when awake but not in a car. I intend to wear my helmet in the winter when I go on long walks. I suspect that we would be better off if there was a social norm of everyone wearing helmets all the time. I have considered whether I should wear my helmet when I'm at home. (I'm over 40.) If the helmet was invisible I would wear it all the time.

comment by Lumifer · 2015-07-30T18:21:51.927Z · score: -2 (10 votes) · LW(p) · GW(p)

I suspect that we would be better off if there was a social norm of everyone wearing helmets all the time.

No, you mean that there will be some decrease in injuries/deaths. Whether we would be "better off" requires considering the cost part of the equation as well (not to mention picking the metric for "better").

For example, a similar social norm of never ever going swimming would also result in a decrease in deaths. Would it make us "better off"?

comment by James_Miller · 2015-07-30T18:25:32.309Z · score: 3 (3 votes) · LW(p) · GW(p)

Sorry for being unclear. By saying "better off" I did intend to take into account the cost of wearing a helmet. Currently, this cost would be high because others would think less of the wearer. When I was young, no one wore a bicycle helmet, now not forcing your kid to wear one would, in my neighborhood at least, be considered bad parenting so it's more costly for a parent to not make his kid wear a bike helmet than to force him to use one.

comment by Lumifer · 2015-07-30T18:50:37.272Z · score: 0 (2 votes) · LW(p) · GW(p)

I don't think that the (dis)approval of neighbours is the largest cost component, but there is a bigger issue.

In doing the cost-benefit analysis that involves uncertainty, a major factor is risk aversion. When you say "we would be better off" you imply that a particular level of risk aversion -- similar to yours, in this case -- would be optimal in some way. Why do you think so?

For example, my risk aversion seems to be noticeably lower than yours. On the basis of which criteria do you think that your level of risk aversion is more suitable as a social norm than mine?

comment by James_Miller · 2015-07-30T19:09:55.012Z · score: 2 (2 votes) · LW(p) · GW(p)

I'm guessing that the utility of the average American would be higher if the social norm was (a) you are weird if you don't wear a helmet most of the time when awake, then what we have today which is (b) you are weird if you do wear a helmet most of the time when awake.

comment by btrettel · 2015-07-31T17:08:11.110Z · score: 1 (1 votes) · LW(p) · GW(p)

Some helmets are more acceptable than others. I've had people say things like "You know you are inside now" to me when I take the elevator to my office and still have my bike helmet on. I do take it off when I get to my office. In contrast, hard hats are generally seen as reasonable to wear for certain people even when they are not on a construction site. The presumption is that someone wearing a hard hat does work in construction or something similar and just didn't want to take the hat off, I suppose.

comment by David_Bolin · 2015-07-31T15:46:59.458Z · score: 0 (0 votes) · LW(p) · GW(p)

I would agree with the social norm of never ever going swimming. In fact, I have a very hard time understanding why people are so willing to basically immerse themselves in an environment so deadly to human beings. I certainly never do it myself.

comment by Lumifer · 2015-07-31T15:51:26.502Z · score: 2 (2 votes) · LW(p) · GW(p)

There is a difference between "I don't want to do X" and "I don't want other people to do X".

Desiring your peculiarities to become social norms is ill-advised, I'd say. You might find other people's peculiarities to be not to your liking.

comment by Tem42 · 2015-07-31T05:38:42.189Z · score: 5 (5 votes) · LW(p) · GW(p)

For some reason your link is not loading for me, but here is another CDC link: Percent Distributions of TBI-related Emergency Department Visits by Age Group and Injury Mechanism . Falls are big causes of TBI for the under four crowd and the over 65 crowd. The 5-14 and 45-64 groups also fall a lot... but only about half as much. But, also look at this: Percent Distributions of TBI-related Deaths by Age Group and Injury Mechanism.

comment by DanielVarga · 2015-07-31T12:59:50.631Z · score: 0 (0 votes) · LW(p) · GW(p)

Oh my god, look at 0-4-year old assaults, both ED visits and deaths. (Assault is the leading TBI-related cause of death for 0-4-year olds.) Some of those falling 4 year olds were assaulted.

comment by Lumifer · 2015-07-31T14:25:30.612Z · score: 1 (1 votes) · LW(p) · GW(p)

Yes. You don't want to be a child of someone with low IQ and anger management problems.

comment by VoiceOfRa · 2015-08-02T20:00:18.603Z · score: 4 (4 votes) · LW(p) · GW(p)

Or worse, a step-child.

comment by Daniel_Burfoot · 2015-07-30T23:21:07.629Z · score: 4 (4 votes) · LW(p) · GW(p)

Would you recommend putting on a helmet as soon as you get out of bed in the morning

I suspect a large fraction of TBIs due to falling are related to icy winter weather; putting on a helmet when you go outside in the winter doesn't sound like a bad idea at all.

comment by Lumifer · 2015-07-31T01:55:06.501Z · score: 1 (3 votes) · LW(p) · GW(p)

I suspect another large fraction of TBIs is due to falling in baths and showers. Still a good idea to put on a helmet?

comment by Vaniver · 2015-07-31T02:22:41.011Z · score: 6 (6 votes) · LW(p) · GW(p)

It's certainly worth investing in a non-slip mat for your bathtub / shower.

Actually... why are bathtubs made of ceramic, instead of rubber or something soft? Cost? Durability / ability to handle water?

comment by Lumifer · 2015-07-31T03:28:14.912Z · score: 6 (6 votes) · LW(p) · GW(p)

why are bathtubs made of ceramic, instead of rubber or something soft?

My guess would be maintenance -- cleaning soft surfaces is difficult. Moreover, wet rubber is very slippery so it will have to be textured and that will make it basically impossible to get clean.

An alternative might be removable soft bumpers.

comment by SolveIt · 2015-07-31T02:23:27.197Z · score: 1 (1 votes) · LW(p) · GW(p)

Have them look like swim caps and drill holes so water can flow? I don't see the problem, it looks like a definite win for elderly people at the very least.

comment by buybuydandavis · 2015-07-31T01:13:03.586Z · score: 1 (1 votes) · LW(p) · GW(p)

Especially if it looks like a ski cap.

comment by Dorikka · 2015-07-31T00:48:24.852Z · score: 4 (4 votes) · LW(p) · GW(p)

Was looking at this in the past, a couple of thoughts. 1. Some articles seem to indicate that repetitive impacts as small as 10g may have cumulative effect. By increasing the effective diameter of the skull, helmets may increase thr likelihood of impact by reducing the necessary angular displacement for the head ro collide with back of seat. As materials of many helmets are tuned for more severe impacts, they may not offer meaningful protection in this domain. 2. Do helmets reduce peripheral vision?

comment by James_Miller · 2015-07-31T01:02:11.996Z · score: 4 (4 votes) · LW(p) · GW(p)

The Crasche hat does not reduce peripheral vision. You can't see it (without a mirror) when it's on your head. The hat is very thin, and the protective material has rubber on the side facing your head and something very strong on the other. You raise valid objections to wearing normal helmets while driving.

comment by Lumifer · 2015-07-31T01:53:38.784Z · score: 2 (2 votes) · LW(p) · GW(p)

The hat is very thin

So does it actually protect against the shock of impact or only against penetrating wounds?

comment by SolveIt · 2015-07-31T02:25:03.424Z · score: 0 (0 votes) · LW(p) · GW(p)

rubber on the side facing your head

Looks like it would mitigate the shock somewhat.

comment by James_Miller · 2015-07-31T02:37:50.819Z · score: 1 (1 votes) · LW(p) · GW(p)

Agreed. It's designed for kids who play sports but are too cool to wear helmets.

comment by Dorikka · 2015-07-31T04:55:27.457Z · score: 0 (0 votes) · LW(p) · GW(p)

Good point. I would be interested in learning what types of impacts (in terms of acceleration, preferably rotational) crasche is designed for, as well as its performance compared to traditional helmets. Do you know of any commonly used metrics that might ve useful for comparing helmets in general? If I remember correctly, the ASME standards use a very high acceptance criteria for linear acceleration (>100g) and do not account for rotational acceleration (which seems to cause most of the damage.)

comment by Lumifer · 2015-07-31T14:42:17.781Z · score: 1 (1 votes) · LW(p) · GW(p)

This helmet is some neoprene (not rigid foam) inside pieces of a plastic shell. It doesn't look capable of passing certifications and the website does not mention any (or, actually, any data on how well it deals with impacts).

comment by Dorikka · 2015-08-07T03:26:14.583Z · score: 0 (0 votes) · LW(p) · GW(p)

I got some info, linking in case you're interested.

comment by Dorikka · 2015-08-06T03:51:17.683Z · score: 0 (0 votes) · LW(p) · GW(p)

Hmph. I sent them an email asking for some quantification of performance, or studies if they have them. Will see what they say.

comment by James_Miller · 2015-07-31T05:32:21.519Z · score: 0 (0 votes) · LW(p) · GW(p)

Sorry, but I don't have the data you request.

comment by Dorikka · 2015-08-07T03:26:41.320Z · score: 0 (0 votes) · LW(p) · GW(p)

I got some info regarding this, linking in case you're interested.

comment by jswan · 2015-08-04T03:46:31.372Z · score: 2 (2 votes) · LW(p) · GW(p)

There are so many variables here. I think most people underestimate the violence involved in a high speed motor vehicle crash. Years ago, I was involved in EMS and responded to a lot of crashes. If we eliminate a) crashes without seatbelts worn (1), and b) crashes without frontal airbags (cars without frontal airbags are relatively uncommon these days, I'd say that most survivable TBIs were caused by either a) side impacts, with the head hitting the window glass, or b) the airbag itself (2). Of those two, the low-to-intermediate-speed side impact is the only one where a helmet would make much difference. Some cars now come with side-curtain airbags, which would help a lot with this.

No doubt, many other crashes result in TBIs, but the forces are so extreme that a small helmet isn't going to help. It's really stunning to see what happens in high-speed impacts.

(1) Without seatbelts, even intermediate-speed impacts result in so much chaotic movement that people tend to fly around inside (or outside) the car and airbags don't help that much. You don't want to be in an ejected-from-vehicle event.

(2) Airbags can definitely cause TBIs by themselves, especially if you're seated very close to them. It's basically a small explosion going off in your face. It's better than hitting the steering wheel or windshield, though.

comment by James_Miller · 2015-08-04T04:14:33.688Z · score: 0 (0 votes) · LW(p) · GW(p)

the low-to-intermediate-speed side impact is the only one where a helmet would make much difference

That seems reasonable.

No doubt, many other crashes result in TBIs, but the forces are so extreme that a small helmet isn't going to help.

For saving a life, but it still might help with preserving more of the brain for cryonics.

I wonder if a helmet would reduce the damage caused by an airbag.

comment by RichardKennaway · 2015-08-04T07:24:40.612Z · score: 2 (2 votes) · LW(p) · GW(p)

I wonder if a helmet would reduce the damage caused by an airbag.

I doubt it.

Ordinary helmets are thick. That isn't to make them stronger. Bicycle helmets are made of something like expanded polystyrene: you can push a fingernail into them. I've never worn a motorbike helmet, but they have thick padding inside.

The reason is to make space between your head and the impacting object, so that the impact forces are spread over a longer time as the helmet material deforms. Acceleration = force/time, so increasing the time reduces the acceleration.

A hard shell spreads the force of the blow over a larger area, but does nothing to reduce the acceleration.

An airbag already hits with a large area, so I don't think the Crasche would have any effect in that situation. It's a hard shell with thin padding, so I expect it is of some value against sharp objects and abrasions, but won't alleviate impact forces much. I wonder what their patent claims are.

comment by RichardKennaway · 2015-08-10T11:28:19.194Z · score: 0 (0 votes) · LW(p) · GW(p)

I wonder what their patent claims are.

To answer my own question, here are some of the patents. The claims consist of the design and method of making the protective inserts, not the sort or amount of protection it gives.

comment by [deleted] · 2015-08-01T12:59:54.486Z · score: 2 (2 votes) · LW(p) · GW(p)

How about wearing a massage vest while walking around. The obvious thing is, it's weird. From experience, actually, the helmet may scrape the roof of your car.

Are there any good massage clothing? The cochrane review on spinal manipulation says it's not better than exercise therapy or massage for chronic lower back pain. Massage costs add up, so I'm wondering what some good options are. Suppose I can solve my 'I'm cold' problem and 'I want a massage problem at once' without adding a 'where do I store this massage item' problem since I already have a wardrobe for clothes. Also, items of clothing which may prompt people to volunteer massages for me are good too. And general tips for getting free massages. I looked for massage swaps online and only found scam pay sites. Suprised there isn't a Tindr for Massages.

It's not as if technological massage solutions don't work. There is evidence some do. The rest haven't been evaluated. I can only find massage vest for areas other than lower back.

All this is suprising given back pain is a major problem. It's not suprising given the disorder of the field, starting from the academics themselves. Even the relevant Cochrane Group doesn't seem to have its affairs in order. Why are there seperate reviews, published on the same day, by the same Primary Review Group, for Back Schools for Non-Specific Low-Back Pain and individual patient education for low-back pain!.

Importantly, there is zero evidence online or anywhere that back schools actually exist outside the ivory tower. It's entirely unclear why this except there is incentive for treating professionals to pretend their treatement is the best rather than campain for pain more broadly.

comment by ChristianKl · 2015-08-03T09:19:29.789Z · score: 0 (0 votes) · LW(p) · GW(p)

If you want massage exchanges the straightforward way is to take a massage course. Talk with the people that attend it. Set up meetings to exchange messages.

comment by philh · 2015-08-01T09:34:01.399Z · score: 2 (2 votes) · LW(p) · GW(p)

With the inserts in, how heavy is this and how small does it fold up? I cycle, and one thing keeping me from wearing a helmet is that I have no easy way to carry one. If I could just keep this in my jacket pocket, there's a decent chance I'd usually wear it.

comment by James_Miller · 2015-08-01T15:13:03.241Z · score: 3 (3 votes) · LW(p) · GW(p)

. If I could just keep this in my jacket pocket, there's a decent chance I'd usually wear it.

I think for large pockets, yes but not for smaller ones.

It is very light, weight wouldn't be an issue.

comment by philh · 2015-08-01T19:41:16.011Z · score: 3 (3 votes) · LW(p) · GW(p)

Thanks! I've ordered one.

comment by Elo · 2015-08-01T09:21:54.066Z · score: 2 (4 votes) · LW(p) · GW(p)

Would it be too much trouble to ask you to update the top post with some of the information in the comments? Thanks.

comment by Username · 2015-08-08T17:46:08.401Z · score: 1 (1 votes) · LW(p) · GW(p)

Thanks for posting this - I'm in a cold climate and have been looking for a beanie with head protection built in. One question - is there a noticeable hard shell under the fabric to the touch?

I've been wanting to get a hat with d3o in it, but I haven't been able to find anything after their announcement a few years ago. Anyone know anything about that?

comment by James_Miller · 2015-08-09T00:31:29.201Z · score: 0 (0 votes) · LW(p) · GW(p)

is there a noticeable hard shell under the fabric to the touch?

Yes, there are several separate hard pieces that go under the fabric.

Never heard of d30 before, but it looks great. I found this


for $100. I have no idea if the supplier is reliable.

comment by ChristianKl · 2015-08-03T08:47:56.149Z · score: 1 (1 votes) · LW(p) · GW(p)

Do you have one? Is it comfortable?

comment by James_Miller · 2015-08-03T15:27:17.591Z · score: 2 (2 votes) · LW(p) · GW(p)

Yes. It's just like wearing a ski cap.

comment by ChristianKl · 2015-08-03T08:47:41.129Z · score: 1 (3 votes) · LW(p) · GW(p)

Given that wearing a helmet likely makes you engage in more dangerous driven habits just as wearing a seatbelt does. It's an effect worth to keep in mind. I also don't know how much added benefit this provides over a simple airbag.

comment by Ishaan · 2015-08-01T22:37:42.276Z · score: 1 (1 votes) · LW(p) · GW(p)

Bulletproof vests have anecdotally saved police officers from car accidents as well.

Seems like the sort of thing you might successfully convince new teen drivers to do despite the weird factor (since they're the highest risk demographic).

Edit: If the hats aren't extremely uncomfortable, might also be good fall protection for the elderly...

comment by James_Miller · 2015-08-02T00:08:22.104Z · score: 1 (1 votes) · LW(p) · GW(p)

I will look into the vests. I wonder if paintball protection vests would work for automobile protection?

If the hats aren't extremely uncomfortable, might also be good fall protection for the elderly...

Strongly agree.

comment by DanielLC · 2015-08-01T21:29:45.562Z · score: 1 (1 votes) · LW(p) · GW(p)

That number is meaningless to me. Can you tell me micromorts per mile or something?

comment by James_Miller · 2015-08-02T00:00:50.789Z · score: 1 (1 votes) · LW(p) · GW(p)

Sorry I don't have an estimate for this. But you are right it would be good to know.

comment by [deleted] · 2015-08-03T00:09:32.026Z · score: 2 (2 votes) · LW(p) · GW(p)

You don't?

comment by James_Miller · 2015-08-03T00:54:11.481Z · score: 1 (1 votes) · LW(p) · GW(p)

Good point.

comment by tanagrabeast · 2015-07-30T23:29:02.654Z · score: 1 (1 votes) · LW(p) · GW(p)

I'm curious about liability risks that may accrue to the very lonely trendsetters who try it.

In my imagination, there's a terrible accident that leaves someone other than the helmet-wearer paralyzed or dead, and investigators are surprised to see that one driver was wearing... a helmet?? It's almost like he knew he was going to get into an accident -- perhaps even intended to. Certainly, that's what people would think reading the articles about it. Perhaps a jury would, as well.

Even a weaker version of that argument could be damaging; anti-lock breaks are said to increase risky driving behavior, after all. The same has been said of seat belts, even. See risk compensation.

comment by James_Miller · 2015-07-30T23:38:53.470Z · score: 5 (5 votes) · LW(p) · GW(p)

In my imagination, there's a terrible accident that leaves someone other than the helmet-wearer paralyzed or dead, and investigators are surprised to see that one driver was wearing... a helmet?? It's almost like he knew he was going to get into an accident -- perhaps even intended to. Certainly, that's what people would think reading the articles about it. Perhaps a jury would, as well.

If this happens to you say you did it because of my blog post. If you pay transportation costs I will even testify for you at a trial.

anti-lock breaks are said to increase risky driving behavior, after all

Economists call this the "Peltzman effect" and it seems robust. It does reduce the social benefits of driving helmets. One economist took the implications of this effect to their logical conclusion and suggested that steering wheels should have a spike pointed at their drivers.

comment by isionous · 2015-08-08T08:16:54.777Z · score: 0 (0 votes) · LW(p) · GW(p)

What do you think of watching car crash compilations to counteract the Peltzman effect?

comment by James_Miller · 2015-08-08T15:19:49.241Z · score: 1 (1 votes) · LW(p) · GW(p)

It might work.

comment by good2108 · 2015-08-05T09:49:47.209Z · score: -1 (1 votes) · LW(p) · GW(p)

i didn't wear helmet while bike driving then how could i wear helmet while driving car?

comment by Vaniver · 2015-08-05T13:01:52.719Z · score: 6 (6 votes) · LW(p) · GW(p)

You don't need to be bound by the value or fact judgments of previous-you.

comment by deepakjnath · 2015-08-03T22:41:55.220Z · score: -2 (2 votes) · LW(p) · GW(p)

No one should stop you or penalize you for wearing a helmet in the car.