Cycle helmet effectiveness in New Zealand

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Abstract

Since late 1989, the cycle helmet wearing rate in New Zealand has risen from around 20% for adults and teenagers, and 40% for younger children, to more than 90% in all age groups. Cycle helmet wearing became mandatory under New Zealand law in January 1994. This paper considers the effect of cycle helmet wearing on hospitalised head injuries between 1990 and 1996, using cyclist limb injuries as a measure of exposure to the risk of cycling trauma. Non-motor vehicle crashes were treated separately from those involving a motor vehicle. Non-motor vehicle crashes were further subdivided by age group. Cyclist head injuries decreased with increasing helmet wearing rates for non-motor vehicle crashes in all age groups, and for motor vehicle crashes. For an increase of 5 percentage points in the helmet wearing rate, the corresponding decreases in head injuries in non-motor vehicle accidents were estimated to be 10.2, 5.3 and 3.2% for children of primary school age (5–12 years), secondary school age (13–18 years), and adults respectively. The corresponding decrease in hospitalisations for motor vehicle crashes was 3.6%. All results were significant at the 95% level. The relatively large increase in helmet wearing associated with the passing of a compulsory helmet wearing law in 1994 reduced head injuries by between 24 and 32% in non-motor vehicle crashes, and by 20% in motor vehicle crashes. No increase or decrease in the severity of head injuries for which cyclists were hospitalised over this period could be detected. This may have been due to the small and highly variable number of ‘high severity’ injuries.

Introduction

Cycling in New Zealand is undertaken both as a means of transport and for recreational purposes. From a 1989–90 travel survey (Land Transport Safety Authority, 1990) it was estimated that cycle trips made up 4% of all wheeled vehicle trips, more trips than by bus but fewer trips than as a vehicle driver or passenger. About one third of all cycling trips were students cycling to or from school, a fifth of trips were adults travelling to or from work, another fifth were for recreational purposes and another fifth were ‘errands’ such as shopping. Ninety percent of cycle trips were made by riders under forty years of age. Most non-recreational cycling in NZ takes place on-road, where cyclists mingle with traffic. Few areas have designated bike paths or separate cycle lanes, and riding on footpaths is not generally permitted.

Cycle helmets have been compulsory for all on-road cyclists in New Zealand since January 1994. Helmets are lightweight with click-fastening chin straps and must conform to Australian/New Zealand Standard 2063 or another internationally recognised standard (Land Transport Safety Authority, 1997). Full-face helmets such as motorcycle helmets are not approved for use by cyclists. The helmet wearing rate increased steadily from the mid 1980s until 1993; since 1994 it has remained fairly static at around 95%. (Estimates of the helmet wearing rate are based on observational surveys of cycle helmet wearing behaviour conducted by the Land Transport Safety Authority (LTSA) from 1986 to 1998).

Adoption patterns varied markedly by age group. Fig. 1 shows the wearing rates separately for each of three age groups, since this type of measurement began in late 1989. The early adoption rate was highest among primary school children (ages 5–12 years) with a voluntary wearing rate of over 80% by 1993. In contrast, the adult wearing rate remained relatively low until the introduction of compulsory helmet legislation.

The number of hospitalised cyclists with head injuries has decreased in recent years, both for cyclists in collisions with motor vehicles and for those injured in crashes where no motor vehicle was involved. While wearing rates appear to have continued at high rates in the last 2 years, hospital data are only available to the end of 1996.

This paper considers the effect of cycle helmet wearing on hospitalised head injuries.

Studies in other jurisdictions have shown substantial reductions in head injury associated with cycle helmet wearing. In a case control study in Seattle, Thompson et al. (1996) compared cyclists killed by or treated for head injury with cyclists treated for other injuries. They found an 85% reduction in the risk of head injury and an 88% reduction in the risk of brain injury for helmeted cyclists relative to accident-involved cyclists without helmets. In Victoria, Carr et al. (1995) evaluated the effects of compulsory helmet wearing during the first 4 years of its implementation, and found a 40% decrease in head injuries attributable to the law change. A similar evaluation of compulsory helmet wearing legislation in South Australia (Marshall and White, 1994) found an 18% reduction in the incidence of head injuries during the 2 years immediately after the legislation was introduced, compared to the pre-law incidence. In New Zealand, Scuffham and Langley (1997) were not able to detect a significant reduction in serious head injury as cycle helmet use increased, during the period preceding mandatory helmet legislation (1980–1992). They did however identify a time effect, which may have captured the helmet effect.

It has been claimed (Robinson, 1996) that requiring the wearing of cycle helmets reduces bicycling. There is no evidence of this from the very sparse information on cyclist numbers available in New Zealand. The observational surveys used to estimate helmet wearing rates were set up to obtain a certain sample size and do not indicate exposure to risk. One would however expect on-road cycling for non-recreational purposes to have decreased over the last 10 or so years, concomitant with a substantial reduction in the cost of motorised transport. This has been brought about by reduced real fuel costs, a major reduction in the cost of buying motor vehicles associated with the importation of used vehicles from Japan and a large reduction in import tariffs on new vehicles.

Alcohol is unlikely to be a confounding factor in this study. As noted earlier, travel to or from work or school accounts for more than half of all cycle trips in New Zealand. Around half of the remaining trips are undertaken by school-age children. Under these circumstances, alcohol would not be expected to play a major part in cycling crashes. Data on the number of injured cyclists who were under the influence of alcohol are available for crashes involving a motor vehicle. The cyclist’s (suspected) consumption of alcohol was recorded as a possible cause of the crash in only 1% of cases.

Section snippets

Data

The New Zealand Health Information Service (NZHIS) holds records of hospital admissions containing patient, crash and diagnosis information. Until the end of 1994, the diagnoses were coded according to the ICD-9-CM system. Since January 1995 the ICD9-CM-A system has been in use. This has resulted in a number of changes to the coding of diagnoses, most notably that the first diagnosis mentioned no longer represents the most serious condition. For this reason, all available diagnosis codes were

Method

Some measure of cyclist exposure to the possibility of head injury was required, to take into account any variations in the level of risk over time. The number of hospitalised cyclists with limb fractures was chosen as an indicator of cyclist accident levels in this study. This measure is unlikely to be affected by helmet wearing. It reflects both the amount of travel done by cyclists and changes to the cycling environment, which includes changes in the nature of cycle use and safety

Non motor vehicle crashes

Fig. 4 shows head injured cyclists as a proportion of all cyclists hospitalised with head injury and/or limb fracture (‘the proportion head injured’) for each age group. The above model was fitted to each of these three data series. Cyclist head injuries decreased with increasing helmet wearing rates for each age group, most strongly among children of primary school age. Results are shown in Table 1.

According to this model, an increase in the helmet wearing rate of 5% (that is, from 90 to 95%,

Injury severity

From Fig. 2 it is clear that the number of cyclists admitted to hospital with head injuries has decreased in recent years. It would be useful to know whether there are any detectable changes in the overall severity of head injuries to cyclists admitted to hospital.

Two scales for assessing injury severity are in common use. The abbreviated injury scale (AIS) assesses severity of injury in relation to the probability of death as a result of the injury, on a six-point scale from 1 (Minor) to 6

Conclusion

The increase in the cycle helmet wearing rate in recent years has reduced the risk of head injury in cycling accidents. An increase of 5 percentage points in the helmet wearing rate corresponds to an estimated decrease in head injuries to cyclists in non-motor vehicle accidents of 10.2, 5.3 and 3.2% for children of primary school age (5–12 years), secondary school age (13–18 years), and adults respectively. The corresponding decrease in hospitalisations for motor vehicle crashes (over all age

Acknowledgements

The assistance of Wayne Jones and Kelly Mara is appreciated.

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