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.
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 ...
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.