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.
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.