Bicycle Helmets and the Prevention of Head Injury

The implementation of effective bicycle helmet programs could have a substantial impact on rates for fatal and nonfatal bicycle-related head injury (4). For example, from 1984 through 1988, if a presumed helmet-use rate of 10% had been increased to 100% (i.e., universal helmet use), an average of 500 fatal and 151,400 nonfatal bicycle-related head injuries could have been prevented each year (4).

Several researchers (2,5,8,12) have recommended that bicyclists use helmets to prevent head injuries. However, controlled studies evaluating the effectiveness of bicycle helmets in bicycle crashes have not been available until recently. In particular, the results of a case-control study in Seattle in 1989 indicated that the use of bicycle helmets reduced the risk for bicycle-related head injury by 74%-85% (1). The findings of other studies that have compared the proportions of helmeted and unhelmeted riders who sustained head injury in bicycle crashes (13-15) detected higher risks for head injury among unhelmeted riders (crude odds ratio=4.2 {13}, 19.6 {14}, and 4.5 {15}). Although other strategies may be useful in preventing bicycle-related injuries (i.e., proper road design and maintenance; improvement in bicycle design, manufacturing, and repair; and bicycle safety training {5,16,17}), the use of these strategies does not eliminate the need for bicycle helmets.

Biomechanical Characteristics of Helmets

Helmets are designed to protect the brain and the skull during an impact (5). Field tests and laboratory studies have been used to assess helmet characteristics and determine the relative effectiveness of different helmet designs.

The testing of bicycle helmets approved by either the American National Standards Institute (ANSI) or the Snell Memorial Foundation indicated that using any helmet will protect the brain and neck during a crash more effectively than not using any helmet at all (18). However, these tests identified potential problems with helmet design, including a tendency for all helmets to slip out of proper position with the unequal application of force; a tendency for hard-shell helmets to slide on concrete, potentially increasing the risk for facial injury in a crash; and a likelihood for soft or no-shell helmets to catch or drag on concrete surfaces, causing the head to decelerate at a faster rate than the rest of the body, which potentially increases the risk for neck injuries (18). Subsequent tests indicated that helmets covered with a hard shell or a micro-shell (i.e., a very thin plastic covering) were least likely to cause injury to the head and neck region (19).

The impact protection provided by different brands of bicycle helmets varies considerably depending on type and brand (20,21). When helmets with crushable polystyrene liners were damaged internally during an impact, they provided less protection during future impacts (21).

Helmet Standards

Three organizations -- ANSI, the Snell Memorial Foundation, and the American Society for Testing and Materials (ASTM) -- have developed voluntary standards for bicycle helmets Table 1. Helmets are tested for the amount of impact protection they provide by dropping the upper torso and helmeted head of a crash-test dummy (i.e., a "helmeted headform") onto a metal anvil and measuring the amount of force on the headform (22). Testing for strap-system strength is done by dropping a weight on the fastened strap; the weight causes weaker strap systems (i.e., straps or buckles) to break. Helmets that meet Snell standards provide better protection against bicycle- related head injury than do helmets that meet the less rigorous ANSI standards (18). The Consumer Product Safety Commission is developing federal standards for bicycle helmets. These standards will apply to all helmets sold in the United States and will most likely be similar to the existing standards.

All three existing standards require that manufacturers include warning labels that advise consumers that helmets are for bicycle use only (e.g., "not for motor-vehicle use" {23}) (24, 25). In addition, manufacturers are required to warn consumers (e.g., by including a warning label in the helmet) that a) a helmet that has sustained an impact should be returned to the manufacturer for inspection or be destroyed and replaced, and b) helmets need to be fitted and securely fastened to the bicyclist's head to provide maximum protection.

Performance in Crash Conditions

The use and performance of bicycle helmets also must be assessed under actual crash conditions (26,27). For example, an assessment of helmets worn by bicyclists who had sustained an impact in a bicycle crash indicated that most impacts occurred below the area of the helmet that is usually tested for impact protection (i.e., the test line) (26). In addition, many of the helmets had been damaged before the crash, particularly those helmets worn by bicycle riders less than 15 years of age. However, none of the riders who were wearing their helmets correctly at the time of the crash sustained serious head injuries, despite the severity of many of the impacts (26).

Current testing standards do not take into account that children less than 6 years of age cannot tolerate the same head impact as older children and adults (27). Furthermore, helmets generally are not designed to fit the heads of children less than 6 years of age; thus, a separate helmet standard may be needed to ensure that helmets provide adequate protection for children in this age group (27).

Barriers to Helmet Use

Although bicycle helmets provide effective protection against bicycle-related head injury, only approximately 18% of bicyclists wear helmets all or most of the time (7). Rates of bicycle helmet use are lowest among those groups for whom rates for bicycle-related head injury are highest (i.e., school-age children). Approximately 15% of riders less than 15 years of age wear helmets (7), a prevalence substantially lower than the year 2000 objective -- a helmet-use rate of at least 50% (32).

Barriers to helmet use include cost, the wearability of bicycle helmets, and a lack of knowledge regarding helmet effectiveness (33). In addition, some school-age children (i.e., children less than 15 years of age) believe that wearing a helmet will result in derision by their peers (34). Among older children and adults, rates for helmet use are influenced by some of the same demographic factors as rates for seat belt use (e.g., age, education, income, and marital status) (14,33), and some of the reasons given for not wearing helmets are similar to those given for not wearing seat belts (e.g., rider was on a short trip, helmets are uncomfortable, and negligence) (14). Approaches to overcoming some of these barriers to helmet use include community-based programs (33) and bicycle helmet legislation, which may be particularly effective among school-age children (34-37).

Next >> Increasing the Use of Bicycle Helmets
Recommendations
Bicycle Helmet Legislation
Organizations that Provide Information on Bicycle Helmet Campaigns
Components of a Community-Based Bicycle Helmet Campaign