Statistics from the Insurance Institute for Highway Safety
Fatality Facts: Bicycles – 2009

Less than two percent of motor vehicle crash deaths are bicyclists. The most serious injuries among a majority of those killed are to the head, highlighting the importance of wearing a bicycle helmet. Helmet use has been estimated to reduce head injury risk by 85 percent.

Ninety-one percent of bicyclists killed in 2009 reportedly weren’t wearing helmets, the same percentage as 2008.