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Bicycles are an important form of exercise, transportation, and recreation in New Zealand.[[1,2]] However, bicycle injuries are a leading contributor to unintentional injury. From 2016 to 2019, cyclist injuries accounted for an average of 9.4 deaths per year and 7.2% of all serious injuries.[[3]] In an effort to reduce cyclist head injury, New Zealand cycle helmet legislation became effective in 1994, requiring all cyclists to use standard approved helmets for all on-road cycling. Subsequently, helmet use increased to above 90% for all ages.[[4]] However, this legislation has generated significant controversy. Detractors criticise it as an ineffective intervention, citing unintended consequences including reduced cyclist participation, increased risk of crash, and therefore net population harm. Population health interventions like mandatory legislation must demonstrate evidence of net individual and population benefit in order to be justified. By consideration of criteria assessing benefits and harms, a recommendation can be made regarding the use of mandatory helmet legislation in New Zealand for the mitigation of unintentional child and adult injury.
Are bicycle helmets effective in reducing head injury risk in event of crash?
Literature investigating the efficacy of bicycle helmet use to prevent injury in the event of a crash consists primarily of case-control studies, with randomised controlled trial precluded given ethical considerations. Three relevant systematic reviews with meta-analysis have been performed.[[5,6,7]] All find helmet use to be associated with a significant odds reduction of head, brain, facial, and fatal injury. However, Attewell et al[[6]] additionally found evidence of a nonsignificant odds increase of neck injury associated with helmet use. Elvik[[8,9]] updated Attewell et al, to adjust for publication bias, and ultimately found concordant results regarding neck injuries. But the most recent review of these three relevant systematic reviews, by Olivier et al[[7]] in 2017, identified limitations of Elvik’s re-analysis. Their meta-analysis of 40 studies yielded an odds reduction of 51% for head, 69% for serious head, 33% for facial, and 65% for fatal head injuries. The odds ratio for neck injury was near null effect (OR=0.96) and no strong evidence of publication or time trend bias was identified.
Biomechanical evidence[[10–12]] supports the conclusions of these meta-analyses, with McNally et al[[10]] by computer simulation finding no evidence of any association between helmet use and neck injury. Although Curnow[[13,14]] has posited that helmet use might exacerbate diffuse axonal injury, McIntosh et al[[15]] have published biomechanical evidence reporting no association of helmet use with angular acceleration, contradicting this hypothesis.
Is mandatory helmet legislation effective in increasing helmet use?
Given that evidence supports the efficacy of helmets in the event of crash to reduce head injury risk, evidence that mandatory helmet legislation increases helmet use will provide indirect support of population benefit.
Karkhaneh et al[[16]] undertook a pertinent systematic review, finding twelve observational before-and-after and non-equivalent control group studies, with one specific to NZ. All reported increased helmet use; baseline rates of 4%–59% increased to 37%–91% following legislation and the pooled odds ratio for helmet use was 4.60. The authors note the plausible confounding effects of the variable promotional activities used to support legislation. However, they refer to evidence that benefit of legislation is conferred even in the absence of rigorous enforcement,[[17–20]] and that fear of enforcement contributes relatively little to reasons for helmet use,[[21]] to ultimately conclude legislation effective in increasing helmet use.
Is mandatory helmet legislation effective in reducing head injury risk?
Evidence that mandatory helmet legislation reduces head injury risk will provide direct support of population benefit. Macpherson et al[[22]] performed a relevant systematic review in 2008 collecting four non-randomised controlled before-and-after studies, all examining legislation applying only to children. Three demonstrated significant benefit of legislation for children in Canada and California. Authors expressed concern regarding paucity of evidence, failure of included studies to measure helmet use, and potential inadequacy of controls. However, they conclude mandatory legislation effective in reducing mortality and head injury risk.
Excluded from review on basis of design were the only two extant publications addressing legislation efficacy in New Zealand. Povey et al[[23]] reported a 20% reduction in cyclist head injuries in motor vehicle crashes for all children and 24% and 34% reductions in non-motor vehicle crashes for primary and secondary school children respectively, using limb injury rates to control for background confounders of injury risk. Robinson[[24]] contended that results were an artefact of baseline trends. However, Wang et al[[25]] in later re-analysis confirmed the validity of the original results. The second publication centred in New Zealand by Scuffham et al[[26]] found when controlling using non-head injury rates that legislation averted 139 head injuries over a three-year period.
Additional pertinent literature has since been published internationally. Importantly, Walter et al[[27]] found when controlling using limb injury rate that legislation in New South Wales contributed a 29% reduction in cyclist head injury. Injury rates showed continued divergence with time, evidencing maintenance of benefit.[[28]] Olivier et al[[29]] demonstrate a 46% reduction in cycling fatalities post-legislation, and an absence of evidence suggesting confounding by the introduction of other road safety measures. Further international evidence supports legislation efficacy among children in Australia,[[30]] Canada[[31,32]] and the USA.[[33–36]] Conflicting evidence comes from publications indicating mixed results for children in Sweden[[37]] and an absence of benefit for children and adults in Canada.[[38]]
Clarke[[39]] used retrospective injury data to conclude that legislation in New Zealand has increased cyclist injury risk by 20% from the period 1988–1991 to 2003–2007. Olivier et al[[40]] contend that Clarke ignores data from the period most directly following introduction of legislation and fails to separate head injuries, for which helmets are a targeted intervention, from other injury types. Additionally, Clarke’s methodology fails to address background confounders and baseline trends and therefore does not evidence a causal association between cyclist injury and the introduction of helmet legislation. The subsequent re-analysis by Olivier et al of injury data from the same period supports a decline in cyclist injury following legislation.[[40]]
Does mandatory helmet legislation reduce cycling participation?
Literature investigating the association between cycling participation and rates of collision have largely concluded an inverse or non-linear relationship, including most recently Jacobsen,[[41]] whose results seemed to evidence a “safety in numbers” effect. Bhatia et al[[42]] identify as limitations confounding and inability to establish the temporal direction of effect; however, the inference remains plausible. Consequently, if helmet legislation reduces cycling participation, the corollary may be an increased risk of crash. Further, reduced participation implies reduced physical activity, itself a population hazard. Both effects engender population harm.
Publications investigating the effect of legislation on cycling participation draw mixed conclusions. Robinson[[43]] used New South Wales and Victorian data to conclude legislation in Australia to have reduced cyclist participation; however, Olivier et al[[40]] note the omission of relevant data which, when included, support the contrary position. Rissel et al[[44]] reported that a repeal of helmet legislation would produce an increase in cyclist participation in Sydney; however, Olivier et al[[45]] criticised their statistical analysis, performing a re-analysis with opposing findings.
Canadian literature evidences no significantly reduced ridership following legislation among children.[[46,47]] Australian literature concurs for cyclists of all ages.[[48,49]] American evidence is contradictory, reporting separately a significantly reduced ridership among children,[[50]] and limited evidence of reduced ridership among high school students.[[51]]
Does helmet use increase the risk of a crash?
Adams et al[[52]] argue that risk compensation might temper helmet efficacy, whereby helmet use yields riskier cyclist behaviour and therefore increased risk of a crash, yielding population harm.
A recent systematic review by Esmaeilikia et al[[53]] identified 23 pertinent studies, with 18 opposing the hypothesis of risk compensation, and only two providing supportive data. One supportive study by Walker[[54]] reported significantly reduced motorist overtaking distance associated with helmet use, but Olivier et al[[55]] performed a multivariate re-analysis, categorising overtaking distance according to the typically recommended safe distance of 1m, finding no association of helmet use with unsafe passing.
Review authors considered most included studies inadequate, as they did not directly measure cyclist risk compensation, and instead analysed indirect proxies, such as perceived risk, or general risk-taking in non-cycling contexts. No randomised trials were identified, though a single random crossover design study was performed which did not support risk compensation.[[56]] Overall, the current systematic review has found little to no support that bicycle helmet use is associated with engaging in risky behaviour, though there certainly exists a paucity of high-quality evidence.
Does mandatory helmet legislation provide total population health benefit?
A single publication has attempted to model the total population health impact that mandatory helmet legislation might have in a jurisdiction in which it is enacted.[[57]] Here, De Jong concludes a large negative health impact of legislation in jurisdictions where cycling is already “safe” as defined by model parameters, and a small positive impact in jurisdictions where cycling is considered “unsafe.” However, De Jong’s model assumes that helmet legislation necessarily yields reduced cyclist participation and increased riskiness of behaviour. As demonstrated, these assumptions remain unsupported by the available evidence. When excluding this assumption, Olivier et al[[40]] find De Jong’s model to yield the opposite verdict.
Conclusion
Strong evidence supports that helmet use reduces head injury risk in the event of a crash, and that mandatory helmet legislation increases helmet use and reduces head injury risk for child and adult populations to whom legislation applies. These conclusions provide evidence of the population health benefit of legislation. Conversely, no evidence exists to support that helmet legislation reduces cycling participation, and no strong evidence supports that helmet use increases the risk of a crash, providing no evidence of population health harm. Accordingly, the balance of evidence supports that mandatory helmet legislation is an efficacious population health intervention, and should remain in effect in New Zealand for the mitigation of child and adult unintentional injury.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) Tin Tin S, Woodward A, Ameratunga S. Injuries to pedal cyclists on New Zealand roads, 1988-2007. BMC Public Health. 2010;10(1).
2) Mehan T, Gardner R, Smith G, McKenzie L. Bicycle-Related Injuries Among Children and Adolescents in the United States. Clinical Pediatrics. 2008;48(2):166-173.
3) Te Marutau — Ngā tatauranga ā-tau | Safety — Annual statistics [Internet]. Ministry of Transport. 2021 [cited 26 September 2021]. Available from: https://www.transport.govt.nz/statistics-and-insights/safety-annual-statistics/sheet/cycling-crashes
4) Land Transport (Road User) Rule. 2004.
5) Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. Cochrane database of systematic reviews. 1999;4(2).
6) Attewell RG, Glase K, McFadden M. Bicycle helmet efficacy: A meta-analysis. Accident Analysis & Prevention 2001;33(3):345–52.
7) Olivier J, Creighton P. Bicycle injuries and helmet use: a systematic review and meta-analysis. International Journal of Epidemiology. 2017;46(1):278-292.
8) Elvik R. Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: A re-analysis of Attewell, Glase and McFadden, 2001. Accident Analysis & Prevention 2011;43(3):1245–51.
9) Elvik R. Corrigendum to: ‘Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: a re-analysis of Attewell, Glase and McFadden, 2001’ [Accid Anal Prev 2011;43:1245–51]. Accident Analysis & Prevention 2013;60:245–53.
10) McNally DS, Whitehead S. A computational simulation study of the influence of helmet wearing on head injury risk in adult cyclists. Accident Analysis & Prevention. 2013;60:15-23.
11) Cripton PA, Dressler DM, Stuart CA, Dennison CR, Richards D. Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts. Accident Analysis & Prevention. 2014;70:1-7.
12) Fahlstedt M, Halldin P, Kleiven S. The protective effect of a helmet in three bicycle accidents—A finite element study. Accident Analysis & Prevention. 2016 1;91:135-43.
13) Curnow WJ. The efficacy of bicycle helmets against brain injury. Accident Analysis & Prevention. 2003;35(2):287-92.
14) Curnow WJ. Bicycle helmets and brain injury. Accident Analysis & Prevention. 2007;39(3):433-6.
15) McIntosh AS, Lai A, Schilter E. Bicycle helmets: head impact dynamics in helmeted and unhelmeted oblique impact tests. Traffic injury prevention. 2013;14(5):501-8.
16) Karkhaneh M, Kalenga JC, Hagel BE, Rowe BH. Effectiveness of bicycle helmet legislation to increase helmet use: a systematic review. Injury Prevention. 2006 Apr 1;12(2):76-82.
17) Cameron MH, Vulcan AP, Finch CF, et al. Mandatory bicycle helmet use following a decade of helmet promotion in Victoria, Australia—an evaluation. Accident Analysis & Prevention 1994;26:325–37.
18) Cote TR, Sacks JJ, Lambert-Huber DA, et al. Bicycle helmet use among Maryland children: effect of legislation and education. Pediatrics 1992;89:1216–20.
19) Ni H, Sacks JJ, Curtis L, et al. Evaluation of a statewide bicycle helmet law via multiple measures of helmet use. Arch Pediatr Adolesc Med 1997;151:59–65.
20) Rivara FP, Thompson DC, Patterson MQ, et al. Prevention of bicycle-related injuries: helmets, education, and legislation. Annu Rev Public Health 1998;19:293–318.
21) Finch CF. Teenagers’ attitudes towards bicycle helmets three years after the introduction of mandatory wearing. Injury Prevention 1996;2:126–30.
22) Macpherson A, Spinks A. Cochrane review: Bicycle helmet legislation for the uptake of helmet use and prevention of head injuries. Evidence‐Based Child Health: A Cochrane Review Journal. 2008;3(1):16-32.
23) Povey LJ, Frith WJ, Graham PG. Cycle helmet effectiveness in New Zealand. Accident Analysis & Prevention. 1999;31(6):763-70.
24) Robinson DL. Changes in head injury with the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2001;33(5):687-91.
25) Wang JJ, Grzebieta R, Walter S, Olivier J. An evaluation of the methods used to assess the effectiveness of mandatory bicycle helmet legislation in New Zealand. In Proceedings of the 2013 Australasian College of Road Safety Conference 2013.
26) Scuffham P, Alsop J, Cryer C, Langley JD. Head injuries to bicyclists and the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2000;32(4):565-73.
27) Walter SR, Olivier J, Churches T, Grzebieta R. The impact of compulsory cycle helmet legislation on cyclist head injuries in New South Wales, Australia. Accident Analysis & Prevention. 2011;43(6):2064-71.
28) Olivier J, Walter SR, Grzebieta RH. Long term bicycle related head injury trends for New South Wales, Australia following mandatory helmet legislation. Accident Analysis & Prevention. 2013;50:1128-34.
29) Olivier J, Boufous S, Grzebieta R. The impact of bicycle helmet legislation on cycling fatalities in Australia. International Journal of Epidemiology. 2019 ;48(4):1197-203
30) O’Donovan S, van den Heuvel C, Baldock M, Byard RW. Childhood cycling fatalities in South Australia before and after the introduction of helmet legislation. Medicine, Science and the Law. 2020;60(3):196-9.
31) Lindsay H, Brussoni M. Injuries and helmet use related to non-motorized wheeled activities among pediatric patients. Chronic diseases and injuries in Canada. 2014;34(2-3):74-81.
32) Karkhaneh M, Rowe BH, Saunders LD, Voaklander DC, Hagel BE. Trends in head injuries associated with mandatory bicycle helmet legislation targeting children and adolescents. Accident Analysis & Prevention. 2013;59:206-12.
33) Meehan WP, Lee LK, Fischer CM, Mannix RC. Bicycle Helmet Laws Are Associated with a Lower Fatality Rate from Bicycle–Motor Vehicle Collisions. The Journal of pediatrics. 2013;163(3):726-9.
34) Williams C, Weston R, Feinglass J, Crandall M. Pediatric bicycle helmet legislation and crash-related traumatic brain injury in Illinois, 1999-2009. Journal of surgical research. 2018;222:231-7.
35) Grant D, Rutner SM. The effect of bicycle helmet legislation on bicycling fatalities. Journal of Policy Analysis and Management. 2004 Jun;23(3):595-611.
36) Kett P, Rivara F, Gomez A, Kirk AP, Yantsides C. The effect of an all-ages bicycle helmet law on bicycle-related trauma. Journal of community health. 2016 Dec 1;41(6):1160-6.
37) Bonander C, Nilson F, Andersson R. The effect of the Swedish bicycle helmet law for children: an interrupted time series study. Journal of safety research. 2014;51:15-22.
38) Dennis J, Ramsay T, Turgeon AF, Zarychanski R. Helmet legislation and admissions to hospital for cycling related head injuries in Canadian provinces and territories: interrupted time series analysis. BMJ. 2013;346:f2674
39) Clarke CF. Evaluation of New Zealand's bicycle helmet law. The New Zealand Medical Journal (Online). 2012;125(1349).
40) Olivier J, Wang JJ, Walter S, Grzebieta R. Anti-helmet arguments: Lies, damned lies and flawed statistics. Journal of the Australasian College of Road Safety. 2014;25(4):10.
41) Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Injury prevention. 2003;9(3):205-9.
42) Bhatia R, Wier M. “Safety in Numbers” re-examined: Can we make valid or practical inferences from available evidence?. Accident Analysis & Prevention. 2011;43(1):235-40.
43) Robinson DL. Head injuries and bicycle helmet laws. Accident Analysis & Prevention. 1996;28(4):463-75.
44) Rissel C, Wen LM. The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey. Health promotion journal of Australia. 2011;22(3):178-83.
45) Olivier J, Churches T, Walter S, McIntosh A, Grzebieta R. Response to Rissel and Wen: The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey?. Health promotion journal of Australia. 2012;23(1):76-.
46) Macpherson AK, Parkin PC, To TM. Mandatory helmet legislation and children's exposure to cycling. Injury Prevention. 2001;7(3):228-30.
47) Dennis J, Potter B, Ramsay T, Zarychanski R. The effects of provincial bicycle helmet legislation on helmet use and bicycle ridership in Canada. Injury Prevention. 2010;16(4):219-24.
48) Haworth NL, Schramm AJ, King MJ, Steinhardt DA. Bicycle helmet research: CARRS-Q monograph 5. Centre for Accident Research and Road Safety-Queensland, Queensland University of Technology; 2010.
49) Olivier J, Boufous S, Grzebieta RH. No strong evidence bicycle helmet legislation deters cycling. Med J Aust. 2016;205(2):54-5.
50) Carpenter CS, Stehr M. Intended and unintended consequences of youth bicycle helmet laws. The Journal of Law and Economics. 2011;54(2):305-24.
51) Kraemer JD. Helmet laws, helmet use, and bicycle ridership. Journal of Adolescent Health. 2016;59(3):338-44.
52) Adams J, Hillman M. The risk compensation theory and bicycle helmets. Injury Prevention. 2001;7(2):89-91.
53) Esmaeilikia M, Radun I, Grzebieta R, Olivier J. Bicycle helmets and risky behaviour: A systematic review. Transportation research part F: traffic psychology and behaviour. 2019 Jan 1;60:299-310.
54) Walker I. Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender. Accident Analysis & Prevention. 2007 Mar 1;39(2):417-25.
55) Olivier J, Walter SR. Bicycle helmet wearing is not associated with close motor vehicle passing: a re-analysis of Walker, 2007. PLoS One. 2013 Sep 25;8(9):e75424.
56) Fyhri A, Sundfør HB, Weber C, Phillips RO. Risk compensation theory and bicycle helmets–Results from an experiment of cycling speed and short-term effects of habituation. Transportation Research Part F: Traffic Psychology and Behaviour. 2018 Oct 1;58:329-38.
57) De Jong P. The health impact of mandatory bicycle helmet laws. Risk analysis. 2012 May 1;32(5):782-90.
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Bicycles are an important form of exercise, transportation, and recreation in New Zealand.[[1,2]] However, bicycle injuries are a leading contributor to unintentional injury. From 2016 to 2019, cyclist injuries accounted for an average of 9.4 deaths per year and 7.2% of all serious injuries.[[3]] In an effort to reduce cyclist head injury, New Zealand cycle helmet legislation became effective in 1994, requiring all cyclists to use standard approved helmets for all on-road cycling. Subsequently, helmet use increased to above 90% for all ages.[[4]] However, this legislation has generated significant controversy. Detractors criticise it as an ineffective intervention, citing unintended consequences including reduced cyclist participation, increased risk of crash, and therefore net population harm. Population health interventions like mandatory legislation must demonstrate evidence of net individual and population benefit in order to be justified. By consideration of criteria assessing benefits and harms, a recommendation can be made regarding the use of mandatory helmet legislation in New Zealand for the mitigation of unintentional child and adult injury.
Are bicycle helmets effective in reducing head injury risk in event of crash?
Literature investigating the efficacy of bicycle helmet use to prevent injury in the event of a crash consists primarily of case-control studies, with randomised controlled trial precluded given ethical considerations. Three relevant systematic reviews with meta-analysis have been performed.[[5,6,7]] All find helmet use to be associated with a significant odds reduction of head, brain, facial, and fatal injury. However, Attewell et al[[6]] additionally found evidence of a nonsignificant odds increase of neck injury associated with helmet use. Elvik[[8,9]] updated Attewell et al, to adjust for publication bias, and ultimately found concordant results regarding neck injuries. But the most recent review of these three relevant systematic reviews, by Olivier et al[[7]] in 2017, identified limitations of Elvik’s re-analysis. Their meta-analysis of 40 studies yielded an odds reduction of 51% for head, 69% for serious head, 33% for facial, and 65% for fatal head injuries. The odds ratio for neck injury was near null effect (OR=0.96) and no strong evidence of publication or time trend bias was identified.
Biomechanical evidence[[10–12]] supports the conclusions of these meta-analyses, with McNally et al[[10]] by computer simulation finding no evidence of any association between helmet use and neck injury. Although Curnow[[13,14]] has posited that helmet use might exacerbate diffuse axonal injury, McIntosh et al[[15]] have published biomechanical evidence reporting no association of helmet use with angular acceleration, contradicting this hypothesis.
Is mandatory helmet legislation effective in increasing helmet use?
Given that evidence supports the efficacy of helmets in the event of crash to reduce head injury risk, evidence that mandatory helmet legislation increases helmet use will provide indirect support of population benefit.
Karkhaneh et al[[16]] undertook a pertinent systematic review, finding twelve observational before-and-after and non-equivalent control group studies, with one specific to NZ. All reported increased helmet use; baseline rates of 4%–59% increased to 37%–91% following legislation and the pooled odds ratio for helmet use was 4.60. The authors note the plausible confounding effects of the variable promotional activities used to support legislation. However, they refer to evidence that benefit of legislation is conferred even in the absence of rigorous enforcement,[[17–20]] and that fear of enforcement contributes relatively little to reasons for helmet use,[[21]] to ultimately conclude legislation effective in increasing helmet use.
Is mandatory helmet legislation effective in reducing head injury risk?
Evidence that mandatory helmet legislation reduces head injury risk will provide direct support of population benefit. Macpherson et al[[22]] performed a relevant systematic review in 2008 collecting four non-randomised controlled before-and-after studies, all examining legislation applying only to children. Three demonstrated significant benefit of legislation for children in Canada and California. Authors expressed concern regarding paucity of evidence, failure of included studies to measure helmet use, and potential inadequacy of controls. However, they conclude mandatory legislation effective in reducing mortality and head injury risk.
Excluded from review on basis of design were the only two extant publications addressing legislation efficacy in New Zealand. Povey et al[[23]] reported a 20% reduction in cyclist head injuries in motor vehicle crashes for all children and 24% and 34% reductions in non-motor vehicle crashes for primary and secondary school children respectively, using limb injury rates to control for background confounders of injury risk. Robinson[[24]] contended that results were an artefact of baseline trends. However, Wang et al[[25]] in later re-analysis confirmed the validity of the original results. The second publication centred in New Zealand by Scuffham et al[[26]] found when controlling using non-head injury rates that legislation averted 139 head injuries over a three-year period.
Additional pertinent literature has since been published internationally. Importantly, Walter et al[[27]] found when controlling using limb injury rate that legislation in New South Wales contributed a 29% reduction in cyclist head injury. Injury rates showed continued divergence with time, evidencing maintenance of benefit.[[28]] Olivier et al[[29]] demonstrate a 46% reduction in cycling fatalities post-legislation, and an absence of evidence suggesting confounding by the introduction of other road safety measures. Further international evidence supports legislation efficacy among children in Australia,[[30]] Canada[[31,32]] and the USA.[[33–36]] Conflicting evidence comes from publications indicating mixed results for children in Sweden[[37]] and an absence of benefit for children and adults in Canada.[[38]]
Clarke[[39]] used retrospective injury data to conclude that legislation in New Zealand has increased cyclist injury risk by 20% from the period 1988–1991 to 2003–2007. Olivier et al[[40]] contend that Clarke ignores data from the period most directly following introduction of legislation and fails to separate head injuries, for which helmets are a targeted intervention, from other injury types. Additionally, Clarke’s methodology fails to address background confounders and baseline trends and therefore does not evidence a causal association between cyclist injury and the introduction of helmet legislation. The subsequent re-analysis by Olivier et al of injury data from the same period supports a decline in cyclist injury following legislation.[[40]]
Does mandatory helmet legislation reduce cycling participation?
Literature investigating the association between cycling participation and rates of collision have largely concluded an inverse or non-linear relationship, including most recently Jacobsen,[[41]] whose results seemed to evidence a “safety in numbers” effect. Bhatia et al[[42]] identify as limitations confounding and inability to establish the temporal direction of effect; however, the inference remains plausible. Consequently, if helmet legislation reduces cycling participation, the corollary may be an increased risk of crash. Further, reduced participation implies reduced physical activity, itself a population hazard. Both effects engender population harm.
Publications investigating the effect of legislation on cycling participation draw mixed conclusions. Robinson[[43]] used New South Wales and Victorian data to conclude legislation in Australia to have reduced cyclist participation; however, Olivier et al[[40]] note the omission of relevant data which, when included, support the contrary position. Rissel et al[[44]] reported that a repeal of helmet legislation would produce an increase in cyclist participation in Sydney; however, Olivier et al[[45]] criticised their statistical analysis, performing a re-analysis with opposing findings.
Canadian literature evidences no significantly reduced ridership following legislation among children.[[46,47]] Australian literature concurs for cyclists of all ages.[[48,49]] American evidence is contradictory, reporting separately a significantly reduced ridership among children,[[50]] and limited evidence of reduced ridership among high school students.[[51]]
Does helmet use increase the risk of a crash?
Adams et al[[52]] argue that risk compensation might temper helmet efficacy, whereby helmet use yields riskier cyclist behaviour and therefore increased risk of a crash, yielding population harm.
A recent systematic review by Esmaeilikia et al[[53]] identified 23 pertinent studies, with 18 opposing the hypothesis of risk compensation, and only two providing supportive data. One supportive study by Walker[[54]] reported significantly reduced motorist overtaking distance associated with helmet use, but Olivier et al[[55]] performed a multivariate re-analysis, categorising overtaking distance according to the typically recommended safe distance of 1m, finding no association of helmet use with unsafe passing.
Review authors considered most included studies inadequate, as they did not directly measure cyclist risk compensation, and instead analysed indirect proxies, such as perceived risk, or general risk-taking in non-cycling contexts. No randomised trials were identified, though a single random crossover design study was performed which did not support risk compensation.[[56]] Overall, the current systematic review has found little to no support that bicycle helmet use is associated with engaging in risky behaviour, though there certainly exists a paucity of high-quality evidence.
Does mandatory helmet legislation provide total population health benefit?
A single publication has attempted to model the total population health impact that mandatory helmet legislation might have in a jurisdiction in which it is enacted.[[57]] Here, De Jong concludes a large negative health impact of legislation in jurisdictions where cycling is already “safe” as defined by model parameters, and a small positive impact in jurisdictions where cycling is considered “unsafe.” However, De Jong’s model assumes that helmet legislation necessarily yields reduced cyclist participation and increased riskiness of behaviour. As demonstrated, these assumptions remain unsupported by the available evidence. When excluding this assumption, Olivier et al[[40]] find De Jong’s model to yield the opposite verdict.
Conclusion
Strong evidence supports that helmet use reduces head injury risk in the event of a crash, and that mandatory helmet legislation increases helmet use and reduces head injury risk for child and adult populations to whom legislation applies. These conclusions provide evidence of the population health benefit of legislation. Conversely, no evidence exists to support that helmet legislation reduces cycling participation, and no strong evidence supports that helmet use increases the risk of a crash, providing no evidence of population health harm. Accordingly, the balance of evidence supports that mandatory helmet legislation is an efficacious population health intervention, and should remain in effect in New Zealand for the mitigation of child and adult unintentional injury.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) Tin Tin S, Woodward A, Ameratunga S. Injuries to pedal cyclists on New Zealand roads, 1988-2007. BMC Public Health. 2010;10(1).
2) Mehan T, Gardner R, Smith G, McKenzie L. Bicycle-Related Injuries Among Children and Adolescents in the United States. Clinical Pediatrics. 2008;48(2):166-173.
3) Te Marutau — Ngā tatauranga ā-tau | Safety — Annual statistics [Internet]. Ministry of Transport. 2021 [cited 26 September 2021]. Available from: https://www.transport.govt.nz/statistics-and-insights/safety-annual-statistics/sheet/cycling-crashes
4) Land Transport (Road User) Rule. 2004.
5) Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. Cochrane database of systematic reviews. 1999;4(2).
6) Attewell RG, Glase K, McFadden M. Bicycle helmet efficacy: A meta-analysis. Accident Analysis & Prevention 2001;33(3):345–52.
7) Olivier J, Creighton P. Bicycle injuries and helmet use: a systematic review and meta-analysis. International Journal of Epidemiology. 2017;46(1):278-292.
8) Elvik R. Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: A re-analysis of Attewell, Glase and McFadden, 2001. Accident Analysis & Prevention 2011;43(3):1245–51.
9) Elvik R. Corrigendum to: ‘Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: a re-analysis of Attewell, Glase and McFadden, 2001’ [Accid Anal Prev 2011;43:1245–51]. Accident Analysis & Prevention 2013;60:245–53.
10) McNally DS, Whitehead S. A computational simulation study of the influence of helmet wearing on head injury risk in adult cyclists. Accident Analysis & Prevention. 2013;60:15-23.
11) Cripton PA, Dressler DM, Stuart CA, Dennison CR, Richards D. Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts. Accident Analysis & Prevention. 2014;70:1-7.
12) Fahlstedt M, Halldin P, Kleiven S. The protective effect of a helmet in three bicycle accidents—A finite element study. Accident Analysis & Prevention. 2016 1;91:135-43.
13) Curnow WJ. The efficacy of bicycle helmets against brain injury. Accident Analysis & Prevention. 2003;35(2):287-92.
14) Curnow WJ. Bicycle helmets and brain injury. Accident Analysis & Prevention. 2007;39(3):433-6.
15) McIntosh AS, Lai A, Schilter E. Bicycle helmets: head impact dynamics in helmeted and unhelmeted oblique impact tests. Traffic injury prevention. 2013;14(5):501-8.
16) Karkhaneh M, Kalenga JC, Hagel BE, Rowe BH. Effectiveness of bicycle helmet legislation to increase helmet use: a systematic review. Injury Prevention. 2006 Apr 1;12(2):76-82.
17) Cameron MH, Vulcan AP, Finch CF, et al. Mandatory bicycle helmet use following a decade of helmet promotion in Victoria, Australia—an evaluation. Accident Analysis & Prevention 1994;26:325–37.
18) Cote TR, Sacks JJ, Lambert-Huber DA, et al. Bicycle helmet use among Maryland children: effect of legislation and education. Pediatrics 1992;89:1216–20.
19) Ni H, Sacks JJ, Curtis L, et al. Evaluation of a statewide bicycle helmet law via multiple measures of helmet use. Arch Pediatr Adolesc Med 1997;151:59–65.
20) Rivara FP, Thompson DC, Patterson MQ, et al. Prevention of bicycle-related injuries: helmets, education, and legislation. Annu Rev Public Health 1998;19:293–318.
21) Finch CF. Teenagers’ attitudes towards bicycle helmets three years after the introduction of mandatory wearing. Injury Prevention 1996;2:126–30.
22) Macpherson A, Spinks A. Cochrane review: Bicycle helmet legislation for the uptake of helmet use and prevention of head injuries. Evidence‐Based Child Health: A Cochrane Review Journal. 2008;3(1):16-32.
23) Povey LJ, Frith WJ, Graham PG. Cycle helmet effectiveness in New Zealand. Accident Analysis & Prevention. 1999;31(6):763-70.
24) Robinson DL. Changes in head injury with the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2001;33(5):687-91.
25) Wang JJ, Grzebieta R, Walter S, Olivier J. An evaluation of the methods used to assess the effectiveness of mandatory bicycle helmet legislation in New Zealand. In Proceedings of the 2013 Australasian College of Road Safety Conference 2013.
26) Scuffham P, Alsop J, Cryer C, Langley JD. Head injuries to bicyclists and the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2000;32(4):565-73.
27) Walter SR, Olivier J, Churches T, Grzebieta R. The impact of compulsory cycle helmet legislation on cyclist head injuries in New South Wales, Australia. Accident Analysis & Prevention. 2011;43(6):2064-71.
28) Olivier J, Walter SR, Grzebieta RH. Long term bicycle related head injury trends for New South Wales, Australia following mandatory helmet legislation. Accident Analysis & Prevention. 2013;50:1128-34.
29) Olivier J, Boufous S, Grzebieta R. The impact of bicycle helmet legislation on cycling fatalities in Australia. International Journal of Epidemiology. 2019 ;48(4):1197-203
30) O’Donovan S, van den Heuvel C, Baldock M, Byard RW. Childhood cycling fatalities in South Australia before and after the introduction of helmet legislation. Medicine, Science and the Law. 2020;60(3):196-9.
31) Lindsay H, Brussoni M. Injuries and helmet use related to non-motorized wheeled activities among pediatric patients. Chronic diseases and injuries in Canada. 2014;34(2-3):74-81.
32) Karkhaneh M, Rowe BH, Saunders LD, Voaklander DC, Hagel BE. Trends in head injuries associated with mandatory bicycle helmet legislation targeting children and adolescents. Accident Analysis & Prevention. 2013;59:206-12.
33) Meehan WP, Lee LK, Fischer CM, Mannix RC. Bicycle Helmet Laws Are Associated with a Lower Fatality Rate from Bicycle–Motor Vehicle Collisions. The Journal of pediatrics. 2013;163(3):726-9.
34) Williams C, Weston R, Feinglass J, Crandall M. Pediatric bicycle helmet legislation and crash-related traumatic brain injury in Illinois, 1999-2009. Journal of surgical research. 2018;222:231-7.
35) Grant D, Rutner SM. The effect of bicycle helmet legislation on bicycling fatalities. Journal of Policy Analysis and Management. 2004 Jun;23(3):595-611.
36) Kett P, Rivara F, Gomez A, Kirk AP, Yantsides C. The effect of an all-ages bicycle helmet law on bicycle-related trauma. Journal of community health. 2016 Dec 1;41(6):1160-6.
37) Bonander C, Nilson F, Andersson R. The effect of the Swedish bicycle helmet law for children: an interrupted time series study. Journal of safety research. 2014;51:15-22.
38) Dennis J, Ramsay T, Turgeon AF, Zarychanski R. Helmet legislation and admissions to hospital for cycling related head injuries in Canadian provinces and territories: interrupted time series analysis. BMJ. 2013;346:f2674
39) Clarke CF. Evaluation of New Zealand's bicycle helmet law. The New Zealand Medical Journal (Online). 2012;125(1349).
40) Olivier J, Wang JJ, Walter S, Grzebieta R. Anti-helmet arguments: Lies, damned lies and flawed statistics. Journal of the Australasian College of Road Safety. 2014;25(4):10.
41) Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Injury prevention. 2003;9(3):205-9.
42) Bhatia R, Wier M. “Safety in Numbers” re-examined: Can we make valid or practical inferences from available evidence?. Accident Analysis & Prevention. 2011;43(1):235-40.
43) Robinson DL. Head injuries and bicycle helmet laws. Accident Analysis & Prevention. 1996;28(4):463-75.
44) Rissel C, Wen LM. The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey. Health promotion journal of Australia. 2011;22(3):178-83.
45) Olivier J, Churches T, Walter S, McIntosh A, Grzebieta R. Response to Rissel and Wen: The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey?. Health promotion journal of Australia. 2012;23(1):76-.
46) Macpherson AK, Parkin PC, To TM. Mandatory helmet legislation and children's exposure to cycling. Injury Prevention. 2001;7(3):228-30.
47) Dennis J, Potter B, Ramsay T, Zarychanski R. The effects of provincial bicycle helmet legislation on helmet use and bicycle ridership in Canada. Injury Prevention. 2010;16(4):219-24.
48) Haworth NL, Schramm AJ, King MJ, Steinhardt DA. Bicycle helmet research: CARRS-Q monograph 5. Centre for Accident Research and Road Safety-Queensland, Queensland University of Technology; 2010.
49) Olivier J, Boufous S, Grzebieta RH. No strong evidence bicycle helmet legislation deters cycling. Med J Aust. 2016;205(2):54-5.
50) Carpenter CS, Stehr M. Intended and unintended consequences of youth bicycle helmet laws. The Journal of Law and Economics. 2011;54(2):305-24.
51) Kraemer JD. Helmet laws, helmet use, and bicycle ridership. Journal of Adolescent Health. 2016;59(3):338-44.
52) Adams J, Hillman M. The risk compensation theory and bicycle helmets. Injury Prevention. 2001;7(2):89-91.
53) Esmaeilikia M, Radun I, Grzebieta R, Olivier J. Bicycle helmets and risky behaviour: A systematic review. Transportation research part F: traffic psychology and behaviour. 2019 Jan 1;60:299-310.
54) Walker I. Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender. Accident Analysis & Prevention. 2007 Mar 1;39(2):417-25.
55) Olivier J, Walter SR. Bicycle helmet wearing is not associated with close motor vehicle passing: a re-analysis of Walker, 2007. PLoS One. 2013 Sep 25;8(9):e75424.
56) Fyhri A, Sundfør HB, Weber C, Phillips RO. Risk compensation theory and bicycle helmets–Results from an experiment of cycling speed and short-term effects of habituation. Transportation Research Part F: Traffic Psychology and Behaviour. 2018 Oct 1;58:329-38.
57) De Jong P. The health impact of mandatory bicycle helmet laws. Risk analysis. 2012 May 1;32(5):782-90.
For the PDF of this article,
contact nzmj@nzma.org.nz
View Article PDF
Bicycles are an important form of exercise, transportation, and recreation in New Zealand.[[1,2]] However, bicycle injuries are a leading contributor to unintentional injury. From 2016 to 2019, cyclist injuries accounted for an average of 9.4 deaths per year and 7.2% of all serious injuries.[[3]] In an effort to reduce cyclist head injury, New Zealand cycle helmet legislation became effective in 1994, requiring all cyclists to use standard approved helmets for all on-road cycling. Subsequently, helmet use increased to above 90% for all ages.[[4]] However, this legislation has generated significant controversy. Detractors criticise it as an ineffective intervention, citing unintended consequences including reduced cyclist participation, increased risk of crash, and therefore net population harm. Population health interventions like mandatory legislation must demonstrate evidence of net individual and population benefit in order to be justified. By consideration of criteria assessing benefits and harms, a recommendation can be made regarding the use of mandatory helmet legislation in New Zealand for the mitigation of unintentional child and adult injury.
Are bicycle helmets effective in reducing head injury risk in event of crash?
Literature investigating the efficacy of bicycle helmet use to prevent injury in the event of a crash consists primarily of case-control studies, with randomised controlled trial precluded given ethical considerations. Three relevant systematic reviews with meta-analysis have been performed.[[5,6,7]] All find helmet use to be associated with a significant odds reduction of head, brain, facial, and fatal injury. However, Attewell et al[[6]] additionally found evidence of a nonsignificant odds increase of neck injury associated with helmet use. Elvik[[8,9]] updated Attewell et al, to adjust for publication bias, and ultimately found concordant results regarding neck injuries. But the most recent review of these three relevant systematic reviews, by Olivier et al[[7]] in 2017, identified limitations of Elvik’s re-analysis. Their meta-analysis of 40 studies yielded an odds reduction of 51% for head, 69% for serious head, 33% for facial, and 65% for fatal head injuries. The odds ratio for neck injury was near null effect (OR=0.96) and no strong evidence of publication or time trend bias was identified.
Biomechanical evidence[[10–12]] supports the conclusions of these meta-analyses, with McNally et al[[10]] by computer simulation finding no evidence of any association between helmet use and neck injury. Although Curnow[[13,14]] has posited that helmet use might exacerbate diffuse axonal injury, McIntosh et al[[15]] have published biomechanical evidence reporting no association of helmet use with angular acceleration, contradicting this hypothesis.
Is mandatory helmet legislation effective in increasing helmet use?
Given that evidence supports the efficacy of helmets in the event of crash to reduce head injury risk, evidence that mandatory helmet legislation increases helmet use will provide indirect support of population benefit.
Karkhaneh et al[[16]] undertook a pertinent systematic review, finding twelve observational before-and-after and non-equivalent control group studies, with one specific to NZ. All reported increased helmet use; baseline rates of 4%–59% increased to 37%–91% following legislation and the pooled odds ratio for helmet use was 4.60. The authors note the plausible confounding effects of the variable promotional activities used to support legislation. However, they refer to evidence that benefit of legislation is conferred even in the absence of rigorous enforcement,[[17–20]] and that fear of enforcement contributes relatively little to reasons for helmet use,[[21]] to ultimately conclude legislation effective in increasing helmet use.
Is mandatory helmet legislation effective in reducing head injury risk?
Evidence that mandatory helmet legislation reduces head injury risk will provide direct support of population benefit. Macpherson et al[[22]] performed a relevant systematic review in 2008 collecting four non-randomised controlled before-and-after studies, all examining legislation applying only to children. Three demonstrated significant benefit of legislation for children in Canada and California. Authors expressed concern regarding paucity of evidence, failure of included studies to measure helmet use, and potential inadequacy of controls. However, they conclude mandatory legislation effective in reducing mortality and head injury risk.
Excluded from review on basis of design were the only two extant publications addressing legislation efficacy in New Zealand. Povey et al[[23]] reported a 20% reduction in cyclist head injuries in motor vehicle crashes for all children and 24% and 34% reductions in non-motor vehicle crashes for primary and secondary school children respectively, using limb injury rates to control for background confounders of injury risk. Robinson[[24]] contended that results were an artefact of baseline trends. However, Wang et al[[25]] in later re-analysis confirmed the validity of the original results. The second publication centred in New Zealand by Scuffham et al[[26]] found when controlling using non-head injury rates that legislation averted 139 head injuries over a three-year period.
Additional pertinent literature has since been published internationally. Importantly, Walter et al[[27]] found when controlling using limb injury rate that legislation in New South Wales contributed a 29% reduction in cyclist head injury. Injury rates showed continued divergence with time, evidencing maintenance of benefit.[[28]] Olivier et al[[29]] demonstrate a 46% reduction in cycling fatalities post-legislation, and an absence of evidence suggesting confounding by the introduction of other road safety measures. Further international evidence supports legislation efficacy among children in Australia,[[30]] Canada[[31,32]] and the USA.[[33–36]] Conflicting evidence comes from publications indicating mixed results for children in Sweden[[37]] and an absence of benefit for children and adults in Canada.[[38]]
Clarke[[39]] used retrospective injury data to conclude that legislation in New Zealand has increased cyclist injury risk by 20% from the period 1988–1991 to 2003–2007. Olivier et al[[40]] contend that Clarke ignores data from the period most directly following introduction of legislation and fails to separate head injuries, for which helmets are a targeted intervention, from other injury types. Additionally, Clarke’s methodology fails to address background confounders and baseline trends and therefore does not evidence a causal association between cyclist injury and the introduction of helmet legislation. The subsequent re-analysis by Olivier et al of injury data from the same period supports a decline in cyclist injury following legislation.[[40]]
Does mandatory helmet legislation reduce cycling participation?
Literature investigating the association between cycling participation and rates of collision have largely concluded an inverse or non-linear relationship, including most recently Jacobsen,[[41]] whose results seemed to evidence a “safety in numbers” effect. Bhatia et al[[42]] identify as limitations confounding and inability to establish the temporal direction of effect; however, the inference remains plausible. Consequently, if helmet legislation reduces cycling participation, the corollary may be an increased risk of crash. Further, reduced participation implies reduced physical activity, itself a population hazard. Both effects engender population harm.
Publications investigating the effect of legislation on cycling participation draw mixed conclusions. Robinson[[43]] used New South Wales and Victorian data to conclude legislation in Australia to have reduced cyclist participation; however, Olivier et al[[40]] note the omission of relevant data which, when included, support the contrary position. Rissel et al[[44]] reported that a repeal of helmet legislation would produce an increase in cyclist participation in Sydney; however, Olivier et al[[45]] criticised their statistical analysis, performing a re-analysis with opposing findings.
Canadian literature evidences no significantly reduced ridership following legislation among children.[[46,47]] Australian literature concurs for cyclists of all ages.[[48,49]] American evidence is contradictory, reporting separately a significantly reduced ridership among children,[[50]] and limited evidence of reduced ridership among high school students.[[51]]
Does helmet use increase the risk of a crash?
Adams et al[[52]] argue that risk compensation might temper helmet efficacy, whereby helmet use yields riskier cyclist behaviour and therefore increased risk of a crash, yielding population harm.
A recent systematic review by Esmaeilikia et al[[53]] identified 23 pertinent studies, with 18 opposing the hypothesis of risk compensation, and only two providing supportive data. One supportive study by Walker[[54]] reported significantly reduced motorist overtaking distance associated with helmet use, but Olivier et al[[55]] performed a multivariate re-analysis, categorising overtaking distance according to the typically recommended safe distance of 1m, finding no association of helmet use with unsafe passing.
Review authors considered most included studies inadequate, as they did not directly measure cyclist risk compensation, and instead analysed indirect proxies, such as perceived risk, or general risk-taking in non-cycling contexts. No randomised trials were identified, though a single random crossover design study was performed which did not support risk compensation.[[56]] Overall, the current systematic review has found little to no support that bicycle helmet use is associated with engaging in risky behaviour, though there certainly exists a paucity of high-quality evidence.
Does mandatory helmet legislation provide total population health benefit?
A single publication has attempted to model the total population health impact that mandatory helmet legislation might have in a jurisdiction in which it is enacted.[[57]] Here, De Jong concludes a large negative health impact of legislation in jurisdictions where cycling is already “safe” as defined by model parameters, and a small positive impact in jurisdictions where cycling is considered “unsafe.” However, De Jong’s model assumes that helmet legislation necessarily yields reduced cyclist participation and increased riskiness of behaviour. As demonstrated, these assumptions remain unsupported by the available evidence. When excluding this assumption, Olivier et al[[40]] find De Jong’s model to yield the opposite verdict.
Conclusion
Strong evidence supports that helmet use reduces head injury risk in the event of a crash, and that mandatory helmet legislation increases helmet use and reduces head injury risk for child and adult populations to whom legislation applies. These conclusions provide evidence of the population health benefit of legislation. Conversely, no evidence exists to support that helmet legislation reduces cycling participation, and no strong evidence supports that helmet use increases the risk of a crash, providing no evidence of population health harm. Accordingly, the balance of evidence supports that mandatory helmet legislation is an efficacious population health intervention, and should remain in effect in New Zealand for the mitigation of child and adult unintentional injury.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) Tin Tin S, Woodward A, Ameratunga S. Injuries to pedal cyclists on New Zealand roads, 1988-2007. BMC Public Health. 2010;10(1).
2) Mehan T, Gardner R, Smith G, McKenzie L. Bicycle-Related Injuries Among Children and Adolescents in the United States. Clinical Pediatrics. 2008;48(2):166-173.
3) Te Marutau — Ngā tatauranga ā-tau | Safety — Annual statistics [Internet]. Ministry of Transport. 2021 [cited 26 September 2021]. Available from: https://www.transport.govt.nz/statistics-and-insights/safety-annual-statistics/sheet/cycling-crashes
4) Land Transport (Road User) Rule. 2004.
5) Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. Cochrane database of systematic reviews. 1999;4(2).
6) Attewell RG, Glase K, McFadden M. Bicycle helmet efficacy: A meta-analysis. Accident Analysis & Prevention 2001;33(3):345–52.
7) Olivier J, Creighton P. Bicycle injuries and helmet use: a systematic review and meta-analysis. International Journal of Epidemiology. 2017;46(1):278-292.
8) Elvik R. Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: A re-analysis of Attewell, Glase and McFadden, 2001. Accident Analysis & Prevention 2011;43(3):1245–51.
9) Elvik R. Corrigendum to: ‘Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: a re-analysis of Attewell, Glase and McFadden, 2001’ [Accid Anal Prev 2011;43:1245–51]. Accident Analysis & Prevention 2013;60:245–53.
10) McNally DS, Whitehead S. A computational simulation study of the influence of helmet wearing on head injury risk in adult cyclists. Accident Analysis & Prevention. 2013;60:15-23.
11) Cripton PA, Dressler DM, Stuart CA, Dennison CR, Richards D. Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts. Accident Analysis & Prevention. 2014;70:1-7.
12) Fahlstedt M, Halldin P, Kleiven S. The protective effect of a helmet in three bicycle accidents—A finite element study. Accident Analysis & Prevention. 2016 1;91:135-43.
13) Curnow WJ. The efficacy of bicycle helmets against brain injury. Accident Analysis & Prevention. 2003;35(2):287-92.
14) Curnow WJ. Bicycle helmets and brain injury. Accident Analysis & Prevention. 2007;39(3):433-6.
15) McIntosh AS, Lai A, Schilter E. Bicycle helmets: head impact dynamics in helmeted and unhelmeted oblique impact tests. Traffic injury prevention. 2013;14(5):501-8.
16) Karkhaneh M, Kalenga JC, Hagel BE, Rowe BH. Effectiveness of bicycle helmet legislation to increase helmet use: a systematic review. Injury Prevention. 2006 Apr 1;12(2):76-82.
17) Cameron MH, Vulcan AP, Finch CF, et al. Mandatory bicycle helmet use following a decade of helmet promotion in Victoria, Australia—an evaluation. Accident Analysis & Prevention 1994;26:325–37.
18) Cote TR, Sacks JJ, Lambert-Huber DA, et al. Bicycle helmet use among Maryland children: effect of legislation and education. Pediatrics 1992;89:1216–20.
19) Ni H, Sacks JJ, Curtis L, et al. Evaluation of a statewide bicycle helmet law via multiple measures of helmet use. Arch Pediatr Adolesc Med 1997;151:59–65.
20) Rivara FP, Thompson DC, Patterson MQ, et al. Prevention of bicycle-related injuries: helmets, education, and legislation. Annu Rev Public Health 1998;19:293–318.
21) Finch CF. Teenagers’ attitudes towards bicycle helmets three years after the introduction of mandatory wearing. Injury Prevention 1996;2:126–30.
22) Macpherson A, Spinks A. Cochrane review: Bicycle helmet legislation for the uptake of helmet use and prevention of head injuries. Evidence‐Based Child Health: A Cochrane Review Journal. 2008;3(1):16-32.
23) Povey LJ, Frith WJ, Graham PG. Cycle helmet effectiveness in New Zealand. Accident Analysis & Prevention. 1999;31(6):763-70.
24) Robinson DL. Changes in head injury with the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2001;33(5):687-91.
25) Wang JJ, Grzebieta R, Walter S, Olivier J. An evaluation of the methods used to assess the effectiveness of mandatory bicycle helmet legislation in New Zealand. In Proceedings of the 2013 Australasian College of Road Safety Conference 2013.
26) Scuffham P, Alsop J, Cryer C, Langley JD. Head injuries to bicyclists and the New Zealand bicycle helmet law. Accident Analysis & Prevention. 2000;32(4):565-73.
27) Walter SR, Olivier J, Churches T, Grzebieta R. The impact of compulsory cycle helmet legislation on cyclist head injuries in New South Wales, Australia. Accident Analysis & Prevention. 2011;43(6):2064-71.
28) Olivier J, Walter SR, Grzebieta RH. Long term bicycle related head injury trends for New South Wales, Australia following mandatory helmet legislation. Accident Analysis & Prevention. 2013;50:1128-34.
29) Olivier J, Boufous S, Grzebieta R. The impact of bicycle helmet legislation on cycling fatalities in Australia. International Journal of Epidemiology. 2019 ;48(4):1197-203
30) O’Donovan S, van den Heuvel C, Baldock M, Byard RW. Childhood cycling fatalities in South Australia before and after the introduction of helmet legislation. Medicine, Science and the Law. 2020;60(3):196-9.
31) Lindsay H, Brussoni M. Injuries and helmet use related to non-motorized wheeled activities among pediatric patients. Chronic diseases and injuries in Canada. 2014;34(2-3):74-81.
32) Karkhaneh M, Rowe BH, Saunders LD, Voaklander DC, Hagel BE. Trends in head injuries associated with mandatory bicycle helmet legislation targeting children and adolescents. Accident Analysis & Prevention. 2013;59:206-12.
33) Meehan WP, Lee LK, Fischer CM, Mannix RC. Bicycle Helmet Laws Are Associated with a Lower Fatality Rate from Bicycle–Motor Vehicle Collisions. The Journal of pediatrics. 2013;163(3):726-9.
34) Williams C, Weston R, Feinglass J, Crandall M. Pediatric bicycle helmet legislation and crash-related traumatic brain injury in Illinois, 1999-2009. Journal of surgical research. 2018;222:231-7.
35) Grant D, Rutner SM. The effect of bicycle helmet legislation on bicycling fatalities. Journal of Policy Analysis and Management. 2004 Jun;23(3):595-611.
36) Kett P, Rivara F, Gomez A, Kirk AP, Yantsides C. The effect of an all-ages bicycle helmet law on bicycle-related trauma. Journal of community health. 2016 Dec 1;41(6):1160-6.
37) Bonander C, Nilson F, Andersson R. The effect of the Swedish bicycle helmet law for children: an interrupted time series study. Journal of safety research. 2014;51:15-22.
38) Dennis J, Ramsay T, Turgeon AF, Zarychanski R. Helmet legislation and admissions to hospital for cycling related head injuries in Canadian provinces and territories: interrupted time series analysis. BMJ. 2013;346:f2674
39) Clarke CF. Evaluation of New Zealand's bicycle helmet law. The New Zealand Medical Journal (Online). 2012;125(1349).
40) Olivier J, Wang JJ, Walter S, Grzebieta R. Anti-helmet arguments: Lies, damned lies and flawed statistics. Journal of the Australasian College of Road Safety. 2014;25(4):10.
41) Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Injury prevention. 2003;9(3):205-9.
42) Bhatia R, Wier M. “Safety in Numbers” re-examined: Can we make valid or practical inferences from available evidence?. Accident Analysis & Prevention. 2011;43(1):235-40.
43) Robinson DL. Head injuries and bicycle helmet laws. Accident Analysis & Prevention. 1996;28(4):463-75.
44) Rissel C, Wen LM. The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey. Health promotion journal of Australia. 2011;22(3):178-83.
45) Olivier J, Churches T, Walter S, McIntosh A, Grzebieta R. Response to Rissel and Wen: The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey?. Health promotion journal of Australia. 2012;23(1):76-.
46) Macpherson AK, Parkin PC, To TM. Mandatory helmet legislation and children's exposure to cycling. Injury Prevention. 2001;7(3):228-30.
47) Dennis J, Potter B, Ramsay T, Zarychanski R. The effects of provincial bicycle helmet legislation on helmet use and bicycle ridership in Canada. Injury Prevention. 2010;16(4):219-24.
48) Haworth NL, Schramm AJ, King MJ, Steinhardt DA. Bicycle helmet research: CARRS-Q monograph 5. Centre for Accident Research and Road Safety-Queensland, Queensland University of Technology; 2010.
49) Olivier J, Boufous S, Grzebieta RH. No strong evidence bicycle helmet legislation deters cycling. Med J Aust. 2016;205(2):54-5.
50) Carpenter CS, Stehr M. Intended and unintended consequences of youth bicycle helmet laws. The Journal of Law and Economics. 2011;54(2):305-24.
51) Kraemer JD. Helmet laws, helmet use, and bicycle ridership. Journal of Adolescent Health. 2016;59(3):338-44.
52) Adams J, Hillman M. The risk compensation theory and bicycle helmets. Injury Prevention. 2001;7(2):89-91.
53) Esmaeilikia M, Radun I, Grzebieta R, Olivier J. Bicycle helmets and risky behaviour: A systematic review. Transportation research part F: traffic psychology and behaviour. 2019 Jan 1;60:299-310.
54) Walker I. Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender. Accident Analysis & Prevention. 2007 Mar 1;39(2):417-25.
55) Olivier J, Walter SR. Bicycle helmet wearing is not associated with close motor vehicle passing: a re-analysis of Walker, 2007. PLoS One. 2013 Sep 25;8(9):e75424.
56) Fyhri A, Sundfør HB, Weber C, Phillips RO. Risk compensation theory and bicycle helmets–Results from an experiment of cycling speed and short-term effects of habituation. Transportation Research Part F: Traffic Psychology and Behaviour. 2018 Oct 1;58:329-38.
57) De Jong P. The health impact of mandatory bicycle helmet laws. Risk analysis. 2012 May 1;32(5):782-90.
Contact diana@nzma.org.nz
for the PDF of this article
View Article PDF
Bicycles are an important form of exercise, transportation, and recreation in New Zealand.[[1,2]] However, bicycle injuries are a leading contributor to unintentional injury. From 2016 to 2019, cyclist injuries accounted for an average of 9.4 deaths per year and 7.2% of all serious injuries.[[3]] In an effort to reduce cyclist head injury, New Zealand cycle helmet legislation became effective in 1994, requiring all cyclists to use standard approved helmets for all on-road cycling. Subsequently, helmet use increased to above 90% for all ages.[[4]] However, this legislation has generated significant controversy. Detractors criticise it as an ineffective intervention, citing unintended consequences including reduced cyclist participation, increased risk of crash, and therefore net population harm. Population health interventions like mandatory legislation must demonstrate evidence of net individual and population benefit in order to be justified. By consideration of criteria assessing benefits and harms, a recommendation can be made regarding the use of mandatory helmet legislation in New Zealand for the mitigation of unintentional child and adult injury.
Are bicycle helmets effective in reducing head injury risk in event of crash?
Literature investigating the efficacy of bicycle helmet use to prevent injury in the event of a crash consists primarily of case-control studies, with randomised controlled trial precluded given ethical considerations. Three relevant systematic reviews with meta-analysis have been performed.[[5,6,7]] All find helmet use to be associated with a significant odds reduction of head, brain, facial, and fatal injury. However, Attewell et al[[6]] additionally found evidence of a nonsignificant odds increase of neck injury associated with helmet use. Elvik[[8,9]] updated Attewell et al, to adjust for publication bias, and ultimately found concordant results regarding neck injuries. But the most recent review of these three relevant systematic reviews, by Olivier et al[[7]] in 2017, identified limitations of Elvik’s re-analysis. Their meta-analysis of 40 studies yielded an odds reduction of 51% for head, 69% for serious head, 33% for facial, and 65% for fatal head injuries. The odds ratio for neck injury was near null effect (OR=0.96) and no strong evidence of publication or time trend bias was identified.
Biomechanical evidence[[10–12]] supports the conclusions of these meta-analyses, with McNally et al[[10]] by computer simulation finding no evidence of any association between helmet use and neck injury. Although Curnow[[13,14]] has posited that helmet use might exacerbate diffuse axonal injury, McIntosh et al[[15]] have published biomechanical evidence reporting no association of helmet use with angular acceleration, contradicting this hypothesis.
Is mandatory helmet legislation effective in increasing helmet use?
Given that evidence supports the efficacy of helmets in the event of crash to reduce head injury risk, evidence that mandatory helmet legislation increases helmet use will provide indirect support of population benefit.
Karkhaneh et al[[16]] undertook a pertinent systematic review, finding twelve observational before-and-after and non-equivalent control group studies, with one specific to NZ. All reported increased helmet use; baseline rates of 4%–59% increased to 37%–91% following legislation and the pooled odds ratio for helmet use was 4.60. The authors note the plausible confounding effects of the variable promotional activities used to support legislation. However, they refer to evidence that benefit of legislation is conferred even in the absence of rigorous enforcement,[[17–20]] and that fear of enforcement contributes relatively little to reasons for helmet use,[[21]] to ultimately conclude legislation effective in increasing helmet use.
Is mandatory helmet legislation effective in reducing head injury risk?
Evidence that mandatory helmet legislation reduces head injury risk will provide direct support of population benefit. Macpherson et al[[22]] performed a relevant systematic review in 2008 collecting four non-randomised controlled before-and-after studies, all examining legislation applying only to children. Three demonstrated significant benefit of legislation for children in Canada and California. Authors expressed concern regarding paucity of evidence, failure of included studies to measure helmet use, and potential inadequacy of controls. However, they conclude mandatory legislation effective in reducing mortality and head injury risk.
Excluded from review on basis of design were the only two extant publications addressing legislation efficacy in New Zealand. Povey et al[[23]] reported a 20% reduction in cyclist head injuries in motor vehicle crashes for all children and 24% and 34% reductions in non-motor vehicle crashes for primary and secondary school children respectively, using limb injury rates to control for background confounders of injury risk. Robinson[[24]] contended that results were an artefact of baseline trends. However, Wang et al[[25]] in later re-analysis confirmed the validity of the original results. The second publication centred in New Zealand by Scuffham et al[[26]] found when controlling using non-head injury rates that legislation averted 139 head injuries over a three-year period.
Additional pertinent literature has since been published internationally. Importantly, Walter et al[[27]] found when controlling using limb injury rate that legislation in New South Wales contributed a 29% reduction in cyclist head injury. Injury rates showed continued divergence with time, evidencing maintenance of benefit.[[28]] Olivier et al[[29]] demonstrate a 46% reduction in cycling fatalities post-legislation, and an absence of evidence suggesting confounding by the introduction of other road safety measures. Further international evidence supports legislation efficacy among children in Australia,[[30]] Canada[[31,32]] and the USA.[[33–36]] Conflicting evidence comes from publications indicating mixed results for children in Sweden[[37]] and an absence of benefit for children and adults in Canada.[[38]]
Clarke[[39]] used retrospective injury data to conclude that legislation in New Zealand has increased cyclist injury risk by 20% from the period 1988–1991 to 2003–2007. Olivier et al[[40]] contend that Clarke ignores data from the period most directly following introduction of legislation and fails to separate head injuries, for which helmets are a targeted intervention, from other injury types. Additionally, Clarke’s methodology fails to address background confounders and baseline trends and therefore does not evidence a causal association between cyclist injury and the introduction of helmet legislation. The subsequent re-analysis by Olivier et al of injury data from the same period supports a decline in cyclist injury following legislation.[[40]]
Does mandatory helmet legislation reduce cycling participation?
Literature investigating the association between cycling participation and rates of collision have largely concluded an inverse or non-linear relationship, including most recently Jacobsen,[[41]] whose results seemed to evidence a “safety in numbers” effect. Bhatia et al[[42]] identify as limitations confounding and inability to establish the temporal direction of effect; however, the inference remains plausible. Consequently, if helmet legislation reduces cycling participation, the corollary may be an increased risk of crash. Further, reduced participation implies reduced physical activity, itself a population hazard. Both effects engender population harm.
Publications investigating the effect of legislation on cycling participation draw mixed conclusions. Robinson[[43]] used New South Wales and Victorian data to conclude legislation in Australia to have reduced cyclist participation; however, Olivier et al[[40]] note the omission of relevant data which, when included, support the contrary position. Rissel et al[[44]] reported that a repeal of helmet legislation would produce an increase in cyclist participation in Sydney; however, Olivier et al[[45]] criticised their statistical analysis, performing a re-analysis with opposing findings.
Canadian literature evidences no significantly reduced ridership following legislation among children.[[46,47]] Australian literature concurs for cyclists of all ages.[[48,49]] American evidence is contradictory, reporting separately a significantly reduced ridership among children,[[50]] and limited evidence of reduced ridership among high school students.[[51]]
Does helmet use increase the risk of a crash?
Adams et al[[52]] argue that risk compensation might temper helmet efficacy, whereby helmet use yields riskier cyclist behaviour and therefore increased risk of a crash, yielding population harm.
A recent systematic review by Esmaeilikia et al[[53]] identified 23 pertinent studies, with 18 opposing the hypothesis of risk compensation, and only two providing supportive data. One supportive study by Walker[[54]] reported significantly reduced motorist overtaking distance associated with helmet use, but Olivier et al[[55]] performed a multivariate re-analysis, categorising overtaking distance according to the typically recommended safe distance of 1m, finding no association of helmet use with unsafe passing.
Review authors considered most included studies inadequate, as they did not directly measure cyclist risk compensation, and instead analysed indirect proxies, such as perceived risk, or general risk-taking in non-cycling contexts. No randomised trials were identified, though a single random crossover design study was performed which did not support risk compensation.[[56]] Overall, the current systematic review has found little to no support that bicycle helmet use is associated with engaging in risky behaviour, though there certainly exists a paucity of high-quality evidence.
Does mandatory helmet legislation provide total population health benefit?
A single publication has attempted to model the total population health impact that mandatory helmet legislation might have in a jurisdiction in which it is enacted.[[57]] Here, De Jong concludes a large negative health impact of legislation in jurisdictions where cycling is already “safe” as defined by model parameters, and a small positive impact in jurisdictions where cycling is considered “unsafe.” However, De Jong’s model assumes that helmet legislation necessarily yields reduced cyclist participation and increased riskiness of behaviour. As demonstrated, these assumptions remain unsupported by the available evidence. When excluding this assumption, Olivier et al[[40]] find De Jong’s model to yield the opposite verdict.
Conclusion
Strong evidence supports that helmet use reduces head injury risk in the event of a crash, and that mandatory helmet legislation increases helmet use and reduces head injury risk for child and adult populations to whom legislation applies. These conclusions provide evidence of the population health benefit of legislation. Conversely, no evidence exists to support that helmet legislation reduces cycling participation, and no strong evidence supports that helmet use increases the risk of a crash, providing no evidence of population health harm. Accordingly, the balance of evidence supports that mandatory helmet legislation is an efficacious population health intervention, and should remain in effect in New Zealand for the mitigation of child and adult unintentional injury.
Summary
Abstract
Aim
Method
Results
Conclusion
Author Information
Acknowledgements
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Competing Interests
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An evaluation of mandatory bicycle helmet legislation
In an effort to reduce cyclist head injury, New Zealand cycle helmet legislation became effective in 1994, requiring all cyclists to use standard approved helmets for all on-road cycling. Subsequently, helmet use increased to above 90% for all ages.
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