I'll talk about somewhere I know something about: Portland. OR. I've lived here for 12 years continuously. 14, if I count visits and shorter stays. There is no law that says adults must wear helmets here! Only children. But you will have a hard time finding an adult that isn't wearing a helmet. A very hard time. Without any legal coercion whatsoever the VAST majority of active cyclists of any age are wearing helmets. Nevertheless the daily toll of severely injured and/or killed cyclists increases year over year with no actual increase in the overall size of the cycling population. I wear a helmet anyway, I just don't credit doing so with anything miraculous. For ME my helmet has yet to prove its lifesaving capacity. That is just ME. But thanks to your thoughtfulness, even if I removed my post you have reproduced much of it.