Improving head protection for cyclists, motorcyclists, and car occupants.

It appears from this review of the literature that both linear and angular accelerations are important in the production of injury to the brain. These mechanical inputs to the head result in differential movements or strains in the contents of the head. These strains, if large enough, produce the irreversible loss of function or physical disruptions of neural or other tissue, observed following head impacts. Owing to the difficulties in measuring these strains, criteria for injury levels are written in terms of external movements of the head, and for the more easily measurable linear acceleration rather than angular acceleration. Helmets for motorcyclists provide adequate protection for impacts up to about 8 m/s. Their performance could be improved for front and side impacts to the head, and by matching liner and skull characteristics. Bicycle helmets have both hard and soft shell models with similar impact attenuation properties. The compulsory wearing of these helmets in Victoria appears to have reduced the number of head injuries sustained. For car occupants, only in the U.S.A. is there a measure of the degree of head protection, in that the Head Injury Criterion is used for 50 km/h frontal impacts. Car occupants appear to be susceptible to severe head injury in side impacts. Considerable improvements could be made by providing impact attenuation in the head contact areas on the door, roof and B-pillar. The seat belt provides protection in frontal impacts, which could be improved further with the addition of an air bag, or by wearing a helmet.