As Mikael Colville-Andersen and Hart Noecker of Rebel Metropolis have pointed out, one is much more likely to have a head injury in a car than on a bike. The absolute number of head injuries is staggering in comparison; Stromberg shows that even looking at the number of injuries per hour of travel, which compensates for the fact that there are a lot more drivers than cyclists, the rate of head injuries is not significantly different between walking, cycling or driving.
In fact, if anyone needs a helmet, it is the pedestrian, who has even higher rates of head injuries than cyclists.
... drivers were less careful around helmeted cyclists. ...
It turns out that so many people are turned off cycling by helmets that the the lives saved through the exercise and health benefits of cycling among people is greater than the number of lives saved through helmet use.
Update: CNet reports:
Brain surgeon: There's no point wearing bicycle helmets
A British brain surgeon says cycle helmets are too flimsy and can actually create more danger by creating the illusion of greater safety. ...
As the Telegraph reports, Marsh was speaking at the Hay Literary Festival. There, he threw caution to an erudite wind by saying: "I ride a bike and I never wear a helmet. In the countries where bike helmets are compulsory there has been no reduction in bike injuries whatsoever." ...
Marsh isn't alone in suggesting bike helmets shouldn't be worn. In a 2010 Tedx Talk (video above) Mikael Colville-Andersen, cycling ambassador for Copenhagen, insisted that some research found that cycle helmets actually cause more brain damage.
Moreover, he described society's obsession with safety equipment as "almost pornographic." Why, he wondered, don't pedestrians wear helmets, as they suffer more brain damage than cyclists?
For him, riding without a helmet is also a symbol of the livable city. The problem, as he sees it, is drivers, not cyclists. What would happen, he mused, if drivers were forced to wear helmets? That would surely save lives. It would also destroy car sales.
He believes that some of the biggest proponents of cycle helmets are the car industry and the auto insurance industry, as the more laws there are insisting on cycle helmets, the fewer bikes are sold.