Head injuries to bicyclists and the New Zealand bicycle helmet law

Abstract

The purpose of this study was to examine the effect of helmet wearing and the New Zealand helmet wearing law on serious head injury for cyclists involved in on-road motor vehicle and non-motor vehicle crashes. The study population consisted of three age groups of cyclists (primary school children (ages 5–12 years), secondary school children (ages 13–18 years), and adults (19+ years)) admitted to public hospitals between 1988 and 1996. Data were disaggregated by diagnosis and analysed using negative binomial regression models. Results indicated that there was a positive effect of helmet wearing upon head injury and this effect was relatively consistent across age groups and head injury (diagnosis) types. We conclude that the helmet law has been an effective road safety intervention that has lead to a 19% (90% CI: 14, 23%) reduction in head injury to cyclists over its first 3 years.

Introduction

Head injuries due to cycle crashes have been identified as a significant cause of morbidity in New Zealand (Collins et al., 1993). Case–control studies show that the use of a correctly designed and fitted cycle helmet is an effective strategy for reducing the frequency of head and upper facial injury (Thompson et al., 1989, Thompson et al., 1990, Thompson et al., 1996a, Thompson et al., 1996b, Maimaris et al., 1994, Thomas et al., 1994Acton et al., 1995).

Cycle helmets are also thought to reduce the severity of head injury. Few studies examine the relationship between head injury severity and the protection afforded by helmet wearing. Thompson et al. (1996a) show that cycle helmets reduce the risk of a brain injury by 88% and the risk of a severe brain injury is reduced by 75%, (i.e. helmets afford less protection against more severe injuries). Shafi et al. (1998) showed that helmeted child cylists with a head injury admitted to hospital were more likely to have concussion and less likely to have a serious brain injury compared to head injured non-helmeted child cyclists (i.e. there is possibly a migration of injury severity from more to less severe).

In an effort to reduce head injuries to cyclists, voluntary helmet use has been widely promoted in New Zealand. Sustained programmes promoting regular helmet use saw helmet wearing rates steadily increase from virtually zero in 1986 to 84%, 62%, and 39% for primary school children (aged 5–12 years), secondary school children (13–18 years), and adult commuters (over 18 years), respectively, in September 1992. This was one year prior to the introduction of the helmet law.

The New Zealand cycle helmet regulation, effective from 1 January 1994, requires all cyclists to wear a standard approved cycle helmet for all on-road cycling. At the time when this legislation was introduced, helmet wearing rates increased to above 90% for the three cyclist age groups. For the first 2 years following the introduction of the law, wearing rates for three age groups of cyclists exceeded 92%, with a slight decline in the following year.

An earlier New Zealand study of the effect of voluntary helmet wearing on serious head injury to cyclists (Scuffham and Langley, 1997) found little association between the percentage of cyclists wearing helmets and the percentage of head injuries to injured cyclists. This present study sought to examine the association between helmet wearing rates and the rates of admission to hospital for head injury to cyclists injured on public roads. Our principal hypothesis was that serious head injuries to cyclists decreased as cycle helmet wearing rates increased. We also sought to examine the effect of helmet wearing for different types of head injury (lacerations, intracranial injury including concussion, skull fractures). The type of injury is examined as it is more meaningful to discuss injury types rather than injury severity using, for example, AIS scores. On examination, we found that injury types tended to be described by one AIS score only, so that one is a proxy for the other. For example, 96% of all intracranial injury to cyclists received an AIS score of 2. In addition, we sought to estimate the change in head injuries to cyclists attributable to the helmet wearing law.