Ninety-two percent of bicyclists killed in 2007 reportedly weren't wearing helmets.

American Academy of Orthopaedic Surgeeons (AAOS) Position Statement

Helmet Use by Motorcycle Drivers and Passengers, and Bicyclists

This Position Statement was developed as an educational tool based on the opinion of the authors. It is not a product of a systematic review. Readers are encouraged to consider the information presented and reach their own conclusions.

The American Academy of Orthopaedic Surgeons (AAOS) endorses laws mandating the use of helmets by motorcycle drivers and passengers and bicyclists.

Orthopaedic surgeons, the medical specialists most often called upon to treat injuries to cyclists, believe a significant reduction in fatalities and head injuries could be effected through the implementation of laws mandating the use of helmets by all motorcycle and bicycle drivers and passengers. The AAOS strongly endorses such mandatory helmet laws.

Numerous studies in various parts of the United States have shown that helmet use reduces the severity and cost associated with injuries to motorcycle riders. Federal efforts beginning with the Highway Safety Act of 1966 achieved the passage of state laws mandating helmet use and by 1975, 47 states had enacted such laws. With the Highway Safety Act of 1977, however, Section 208 of which relaxed the pressure on states to have helmet laws, the federal government created the opportunity to measure the effectiveness of helmet use when 27 states repealed their helmet laws in the following three years.

The American Academy of Orthopaedic Surgeons (AAOS) believes that issues of personal freedom should be seen in the context of the fact that the public at large incurs a major part of the cost for injuries to motorcycle riders.

The repeal of helmet laws in many states was based on issues involving some motorcyclists' claims that mandatory use laws infringed on their right to personal freedom. While it can be argued that the states' laws mandating that motorcyclists be licensed to operate the vehicle are a similar infringement, the more important issue is the cost borne by society when a motorcyclist is injured in an accident. Numerous studies have shown that in cases involving motorcyclists who were not wearing helmets, head injuries were more severe, requiring longer, more expensive hospitalization and rehabilitation. Moreover, it has been shown that the public at large bears a major portion of these increased costs, both in the cases where the injured patients' insurance does not cover all the costs associated with care and through the increasing cost of medical insurance premiums. Society must evaluate the claim of infringement on freedom versus the funding of these costs...

...The AAOS believes that mandatory helmet laws should be expanded to cover bicyclists as well as motorcycle riders.

There are more than 85 million bicycle riders in the United States. Americans of all ages have taken up bicycling for fun, health and fitness benefits, and as a mode of transportation. With this increase in popularity, however, has come an increase in bicycle-related injury and death. Approximately 800 bicycle riders are killed each year. More than 540,000 bicyclists visit emergency rooms with injuries every year, and of those, about 67,000 have head injuries. Direct costs of cyclists' injuries due to not using helmets are estimated at $81 million each year.
https://www.aaos.org/about/papers/position/1110.asp(emphasis added, jcr)

Accid Anal Prev. 2007 May;39(3):469-74. Epub 2006 Dec 1.Click here to read Links
School regulations governing bicycle helmet use and head injuries among Japanese junior high school students.
Ichikawa M, Nakahara S.

Department of Community Health, School of International Health, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. masao@md.tsukuba.ac.jp <masao@md.tsukuba.ac.jp>

We examined the effectiveness of school regulations concerning bicycle helmet use in reducing head injuries among student bicycle commuters to junior high schools in the Japanese prefecture of Saitama. This was done by comparing the rates of head injuries and the ratios of head injuries to non-head injuries between junior high schools with and without school regulations concerning helmet use. Bicycle injury data were derived from school insurance records. Information relating to numbers of bicycle commuters and demographics was collected for each school. We identified that the head injury rate was significantly higher in schools that had no regulations governing the use of bicycle helmets (rate ratio 2.97, 95% confidence interval (CI) 1.03-8.56; odds ratio 2.46, 95% CI 0.80-7.60). The observed trend was more prominent in male students than in female students. The actual rate of bicycle injuries did not significantly differ between the schools with and without regulations concerning helmet use. This suggests that students at schools with regulations were no more cautious in riding their bicycles than their counterparts in schools with no regulations, and that there was no significant difference in the traffic environments surrounding each school. Thus implicating that the observed difference in the head injury rate was most accounted for by the presence of school regulations governing helmet use.