Kind of the definitive answer:
Before you hit the comment button and tell me that you know someone whose life was probably saved by a bike helmet, I know someone, too. I also know someone who believes his life was saved by getting a blood test for prostate specific antigen, detecting prostate cancer. But is that sense of salvation actually justified, for the individual or society? Back in New York I strapped on my helmet for a weekend bike ride in Central Park. But I’m not sure I’ll do the same two years from now if I’m commuting to work on a mature Citi Bike system.
Mr. De Jong, who grew up in the Netherlands, observes of Amsterdam: “Nobody wears helmets, and bicycling is regarded as a completely normal, safe activity. You never hear that ‘helmet saved my life’ thing.”