A computational simulation study of the influence of helmet wearing on head injury risk in adult cyclists Simulations were run over a range of bike and car speeds. Bicycle helmets were found to be effective in reducing the severity of head injuries sustained in frequent crashes. They reduced the risk of a severe (greater than AIS3) injury in crashes with head impacts by an average of 40%. In crashes likely to cause up to moderate (AIS2) injuries to an unprotected rider, a helmet eliminated the risk of injury. Helmets were also found to prevent fatal head injuries in some instances. The study demonstrated the effectiveness of helmets over the entire range of speeds. Helmets were also found to be protective of neck injuries in many cases. Helmets offered an increase in protection even when an increase in speed due to risk compensation was factored in. There are illustrations of the simulations on the linked web site.