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.

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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.

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.
A quick google for "high flow dust mask" reveals several options in this exact niche, including designs especially for bikers and also ATV riders.
Thanks for highlighting that. I'll have to try some of these out. Edit: Respro seems to be the dominant brand.
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.
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...

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 ... (read more)

Thanks for researching this.
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?
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.
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.
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...)
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?
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.)

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

... (read more)
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)?
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.
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.

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... (read more)

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.
From the CDC: I bet a lot of TBI is due to being ejected from the vehicle.
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?
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.
I am certain that the P(death|~seat belt) != 1.
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.
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.
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: 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: * "Prevention of head injuries to car occupants. an investigation of interior padding options" AJ McLean, BN Fildes, CN Kloeden, KH Digges… - 1997 * CR 193: "The development of a protective headband for car occupants" (Andersen, White, McLean 2000). https://infrastructure.gov.au/roads/safety/publications/2000/pdf/protect_head_3.pdf * "Further development of a protective headband for car occupants" RWG Anderson, G Ponte, J McLean, R Tiller, S Hill - 2001 h

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:

... (read more)

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... (read more)

"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: 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% *
1Adam Zerner8y
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.
For injuries Rate should be 1.634253963e-08, yielding about $1261.78 lifetime loss.
0Adam Zerner8y
Thank you so much for this analysis!
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.
Do Americans wear seatbelts much? Especially by passengers.
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.
A lot of us don't, but airbags are mandatory.

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.

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.
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.
Good point.
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?
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.
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.

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

... (read more)

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 orthod... (read more)

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.
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/
$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.
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.
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.
Sorry, I'm not seeing where gwern uses 60mph?
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.
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). 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.
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.
You care for more than just mircomorts. You also care for not getting brain damage.
You can measure that in micromorts too, via QALYs.

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?

(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.

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?

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.

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"?
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.
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?
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.
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.
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.
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.
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.
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.
Yes. You don't want to be a child of someone with low IQ and anger management problems.
Or worse, a step-child.
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.
I suspect another large fraction of TBIs is due to falling in baths and showers. Still a good idea to put on a helmet?
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?

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.

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.
Especially if it looks like a ski cap.

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?

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.
So does it actually protect against the shock of impact or only against penetrating wounds?
Looks like it would mitigate the shock somewhat.
Agreed. It's designed for kids who play sports but are too cool to wear helmets.
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.)
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).
I got some info, linking in case you're interested.
Hmph. I sent them an email asking for some quantification of performance, or studies if they have them. Will see what they say.
Sorry, but I don't have the data you request.
I got some info regarding this, linking in case you're interested.

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 on... (read more)

That seems reasonable. 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.
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.
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.

The Crasche hat (at least the version I got, medium of the normal version) was only partly-assembled.

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.

I think for large pockets, yes but not for smaller ones. It is very light, weight wouldn't be an issue.
Thanks! I've ordered one.

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

Do you have one? Is it comfortable?

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

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 wardrob... (read more)

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.

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 ar... (read more)

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. 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.
What do you think of watching car crash compilations to counteract the Peltzman effect?
It might work.

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?

Yes, there are several separate hard pieces that go under the fabric. Never heard of d30 before, but it looks great. I found this http://www.tacprogear.com/Tacprogear_TRUST_Helmet_Pad_System_by_D3O_p/ha-11303.htm for $100. I have no idea if the supplier is reliable.

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.

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...

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

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

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

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

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

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