There's a long-running argument in American cycling about whether wearing helmets really keeps you safer. Skeptics argue that the more people who ride, the safer cycling is, but some people don't like to wear helmets, depressing the number of riders and making it more dangerous for everyone. This discussion never goes very far before reference is made to Amsterdam or Copenhagen, cities in which huge numbers of people ride (e.g., 50% of Copenhageners) but relatively few people wear helmets, as an enjoyable tour through CopenhagenCycleChic will attest. Here, for example, is Elisabeth Rosenthal in the New York Times: 

"The safest biking cities are places like Amsterdam and Copenhagen, where middle-aged commuters are mainstay riders and the fraction of adults in helmets is minuscule. . . . Bicycling advocates say that the problem with pushing helmets isn’t practicality but that helmets make a basically safe activity seem really dangerous. 'The real benefits of bike-sharing in terms of health, transport and emissions derive from getting ordinary people to use it,' said Ceri Woolsgrove, safety officer at the European Cyclists’ Federation. 'And if you say this is wonderful, but you have to wear armor, they won’t. These are normal human beings, not urban warriors.' ”

Having just returned from Denmark--where the cycling truly is wonderful--I can confidently say that the idea that taking off our helmets will make us more like Copenhagen is totally nuts. One might just as well attribute a prophylactic power to speaking Danish, or eating lots of delicious pastries. (Although, come to think of it, associating cycling with the latter would make it a lot more popular.) I can also confidently report that the reason Danes don't wear helmets is----THEY DON'T HAVE TO! Cycling in Copenhagen is ridiculously safe, not because people don't wear helmets but because nearly every street has dedicated bicycle lanes that are separated from traffic. They look like this:

For the most part, these bike lanes are positioned between parked cars and traffic. The only interaction one has with vehicular traffic is when you have to cross the street to turn left, something that law-abiding Danes religiously do with the light. It's an awesome system, and it makes possible scenes like this: 

But get this: Until last Saturday, it was illegal in California for cities to build protected bike lanes. Happily, thanks to AB 1193, a bill supported by the California Bicycle Coalition and signed by Governor Jerry Brown, that is no longer the case. Californians can sign a petition in favor of protected bike lanes in their community here. But until my town gets some, I'm keeping the lid on.