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.
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.