Helmet laws have stopped a lot of people cycling and have done nothing for head injury rates, see Robinson DL. No clear evidence from countries that have enforced the wearing of helmets. BMJ 2006;332: 722-5. http://www.bmj.com/cgi/content/full/332/ 7543/722-a. It also appears that helmets break easily, but don't absorb the impact, see the engineers quoted at http://en.wikipedia.org/wiki/Bicycle_helmet.