Motorcycle helmet effect on a per-crash basis in Thailand and the United States.

Objective: To compare the effectiveness of motorcycle helmets seen in prospective on-the-street motorcycle accident investigations. The data are drawn from two detailed, in-depth studies of motorcycle accidents, in which trained investigators collected extensive accident evidence on-scene immediately after the crash. This article compares helmeted and unhelmeted motorcycle riders on a per-accident basis for fatality rates, the rate of serious (AIS > 2) brain injuries among survivors, or an outcome that involved either of the two.
Methods: Nine hundred motorcycle crashes in Los Angeles and 969 crashes in Thailand were investigated in detail at the accident scenes, including photos of vehicles, skids, damage, and sometimes the rider. Helmets were collected and injury information was obtained from riders and care providers. This evidence was then used to reconstruct collision events to identify speeds, precrash motions, collision contacts, injury causation, and helmet performance.
Results: In both studies, approximately 6% of riders were killed and 20-25% were hospitalized. Overall, unhelmeted riders were two to three times as likely to be killed, and three times as likely to suffer either death or survival with AIS > 2 brain injury. Unhelmeted survivors had three to four times as many AIS > 2 brain injuries as helmeted riders on a per-crash basis. Nearly 100% of riders with AIS > 4 somatic injuries died. Such injuries were 30% of Thailand fatalities and 57% of L.A. fatalities, but only about 2-3% of the overall accident population. Among the 97-98% of riders with AIS < 5 somatic injuries, helmet use could prevent about three-fourths of fatalities and brain injuries.
Conclusions: Helmets were extremely effective in preventing brain injury and death in 97% of the accident population in less-than-extreme crashes. Helmet use cannot prevent all fatalities because many of those killed succumb to below-the-neck injuries that a helmet cannot prevent.