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© 2002 American Public Health Association
RESEARCH AND PRACTICE |
Kimberly M. Auman, Joseph A. Kufera, Michael F. Ballesteros, and Patricia C. Dischinger are with the Charles McC. Mathias Jr National Study Center for Trauma and Emergency Medical Services, University of Maryland, Baltimore. At the time of the study, John E. Smialek was with the Office of the Chief Medical Examiner, Baltimore.
Correspondence: Requests for reprints should be sent to Kimberly M. Auman, MS, National Study Center for Trauma and EMS, University of Maryland, 701 W Pratt St, 5th Floor, Baltimore, MD 21201 (e-mail: Kauman{at}som.umaryland.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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Objectives. This study sought to determine the impact of Maryland’s all-rider motorcycle helmet law (enacted on October 1, 1992) on preventing deaths and traumatic brain injuries among motorcyclists.
Methods. Statewide motorcyclist fatalities occurring during seasonally comparable 33-month periods immediately preceding and following enactment of the law were compared.
Results. The motorcyclist fatality rate dropped from 10.3 per 10 000 registered motorcycles prelaw to 4.5 postlaw despite almost identical numbers of registered motorcycles. Motorcyclists wearing helmets had a lower risk of traumatic brain injury than those not wearing helmets (odds ratio = 0.31, 95% confidence interval = 0.14, 0.68).
Conclusions. Maryland’s controversial motorcycle helmet law appears to be an effective public health policy and may be responsible for saving many lives.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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The debate about the need for motorcycle helmets has been ongoing. In the United States in 1998, 2284 motorcyclists were killed and an additional 49 000 injured in traffic crashes.1 In 1997, motorcycles made up fewer than 2% of all US registered vehicles and accounted for only 0.4% of all vehicle miles traveled; however, per vehicle mile, motorcyclists are about 14 times as likely as passenger car occupants to die in a traffic crash.1
It is well known that motorcycle helmets are effective in preventing or reducing the severity of motorcycle-related head injuries1–16; however, between 1975 and 1983, 28 states either weakened or repealed their helmet use laws. In response to the National Traffic and Motor Vehicle Safety Act of 1966, Maryland mandated in 1967 that all motorcycle operators or passengers wear helmets approved by the state department of motor vehicles. In 1979 this law was weakened to require only minors to wear approved helmets, but on October 1, 1992, a new law reestablishing a helmet requirement for all motorcycle operators and passengers was enacted.
The purpose of the present study was to determine the impact of the most recent helmet law on preventing deaths among motorcyclists in Maryland. We also examined the association, if any, between traumatic brain injury (TBI) and helmet use.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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Study Period
All motorcyclist fatalities occurring on Maryland roadways were identified during the 33 months immediately preceding enactment of the law (January 1, 1990–September 30, 1992) and the seasonally comparable 33 months following the law change (January 1, 1993–September 30, 1995).
Data Abstraction and Linkage
Each motorcyclist autopsy report was reviewed for demographic, injury, and helmet use information. As a means of determining the location of the crash (i.e., urban vs rural) and confirming helmet usage, all motorcycle driver fatalities were linked, via probabilistic linking methods, with police report data to obtain the road name and reference intersection of the crash. The matched records were geocoded through census tract data to differentiate between urban (at least 250 persons per square mile) and rural regions.
Definitions
Traumatic brain injury was defined according to the clinical case definition found in the Guidelines for Surveillance of Central Nervous System Injury, used by the Centers for Disease Control and Prevention.17 In a given case, all available documents (e.g., autopsy report, investigator report, police report, photographs) were used to determine whether the motorcyclist was wearing a helmet. If 2 sources disagreed as to whether a helmet was used, or if there was no indication of helmet usage in the records, helmet use was recorded as "unknown."
Statistical Analysis
Pearson’s 
2 statistic was used in comparing between-group distributions. The Breslow–Day test for homogeneity was used to determine whether the association between TBI and helmet use within the 2 study periods was similar. A P value below .05 represented a statistically significant result. When appropriate, odds ratios (ORs) and their 95% confidence intervals (CIs) are reported.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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Two hundred twelve motorcyclist deaths occurred during the prelaw and postlaw periods. Eighty-nine percent of the victims were drivers, and helmet status could be determined for 190 victims (89.6%).
Prelaw vs Postlaw
Of the 212 fatalities, 130 (61.3%) occurred in the prelaw period and 82 (38.7%) occurred in the postlaw period, representing a 36.9% decrease. There was a significant increase in the number of postlaw motorcyclists who wore helmets (Table 1
). Before the law, 24.6% of motorcyclists involved in fatal crashes wore helmets, as compared with 80.5% after the law.
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There were no statistically significant differences between prelaw and postlaw fatalities with respect to age, sex, race, time of day, time of week, season of year, alcohol use, or geographic region of crash (Table 1
). Overall, the majority of the victims were aged 18 to 29 years (56.6%), male (94.7%), and White (81.6%). More crashes took place on weekends and during the spring and summer months. More than 70% of geocoded motorcyclist fatalities occurred in urban areas (94% linkage match rate). Among fatalities occurring in the postlaw period, the percentage involving TBI decreased, albeit not significantly.
Motorcyclist fatality counts and rates per 10 000 registered vehicles are presented in Table 2. Before enactment of the law, the motorcyclist fatality rate ranged from a low of 7.8 to a high of 10.2 per 10 000 registered vehicles. The rate has since declined to 4.5 despite almost identical numbers of vehicles registered in 1992 and 1996.
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Helmet Use vs Nonuse
TBIs occurred much less frequently among those wearing helmets than among those not wearing helmets in both the prelaw (65.6% vs 88.5%) and the postlaw (72.6% vs 88.9%) periods. Hence, the enactment of the helmet law did not influence the relationship between helmet use and TBI (P = .81). As a result of these findings, fatalities were pooled across study periods to determine whether helmets were effective in preventing TBI. Motorcyclists wearing helmets were significantly less likely than those not wearing helmets to incur a TBI (OR = 0.31; 95% CI = 0.14, 0.68).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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The present data indicate that, in comparisons of similar periods before and after the Maryland mandatory motorcycle helmet law was enacted, the number of motorcycle fatalities decreased by 37%. Our results reinforce the public health benefits of mandatory helmet laws and corroborate similar findings from other states.18–25
Although helmet use is probably responsible for this decrease, other factors may have contributed. The law change may have affected the risk behaviors of drivers or reduced the number of motorcycle sales, high-risk riders, or miles driven.
According to the Maryland Motor Vehicle Administration, the number of registered motorcycles in the state fluctuated between 1990 and 1996, but there was no dominant decreasing trend after the law change. However, the motorcycle fatality rate per 10 000 registered vehicles fell steadily, and the overall decrease for the study period was 56% (from 10.3 in 1992 to 4.5 in 1996). This decrease is consistent with results of studies conducted in California20 and Louisiana.22
The current study also suggests that mandatory helmet laws are associated with increases in helmet usage; our data showed a dramatic increase in the percentage of helmet users among motorcyclist fatalities, from 24.6% to 80.5%. Our helmet use estimate is an underestimation, because misclassification of helmet use is biased toward nonuse. Other studies have reported that compliance rates approach 100% in the presence of a mandatory helmet law.6,18,21,22,24
Our estimate of 80% is below that of other research, because our study population consisted of only fatal accident victims, which would tend to include more individuals not wearing helmets. A study from California revealed similar percentages when only fatal crashes were examined (80.1% with a helmet law vs 21.5% with no law).20
There is additional evidence indicating that helmet laws increase helmet use. A study conducted in Louisiana demonstrated a helmet use decrease followed by an increase with the repeal and reinstatement of a similar law.21,22
The present findings indicate that motorcyclists wearing helmets sustained fewer TBIs than those not wearing helmets. Our results, although consistent with those of a large number of published studies,3–17 represent an underestimate of the protective effect of helmet use in that TBIs among only fatally injured motorcyclists were examined, encompassing the most serious crashes. Injured motorcyclists who use a helmet have a lower mortality rate than those not using a helmet.6,13 Because the present study was based on fatal crashes, our population overrepresented individuals not using helmets.
Increases in the discrepancy in TBIs between those using and not using helmets would be revealed in an analysis based on patients with less severe injuries (e.g., emergency department patients). Other studies have shown that, in addition to preventing head injuries, helmet use is associated with shorter hospital stays,9,13,16,18,21,22 fewer hospital readmissions,13 lower overall injury severity,6,9,11,13,14,26 less need for rehabilitation,16 and lower total hospital costs.9,13,15–18,21,26
Many factors, such as vehicle miles traveled, engine sizes of the motorcycles that crash, and vehicular speed, may confound the relationship between helmet laws and death rates. We did not address these factors, because the data were not available from the police reports.
Another important area that we did not address is type of helmet worn. One study that examined the protective effects of full-face motorcycle helmets vs nonstandard helmets showed that the former were more effective in preventing and mitigating head injuries.27 In fact, when weather, road location, motorcycle type, riding position (driver vs passenger), age, and sex were controlled, use of nonstandard helmets did not statistically differ from nonuse of a helmet with respect to head injury.28 In our study, helmet type was identified in only 5.7% of reviewed cases, because there was no code in the police report records to capture this information.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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We found that, in Maryland, enactment of a mandatory motorcycle helmet law in 1992 was associated with an increase in helmet use and a slight decrease in TBIs among motorcyclists involved in fatal accidents. In addition, motorcyclists wearing helmets were significantly less likely to suffer a TBI than were motorcyclists not wearing helmets. Furthermore, the fatality rate per 10 000 registered motorcycles decreased by 56% over a 5-year period after enactment of the helmet law, despite almost identical numbers of vehicles registered. Our results provide further evidence that Maryland’s controversial motorcycle helmet law appears to be an effective public health policy and may be responsible for saving many lives.
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Acknowledgments |
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This study was supported by the Maryland Department of Transportation (project no. MDOT-99-052).
This article is dedicated to the memory of Dr John E. Smialek, chief medical examiner for the state of Maryland, who died unexpectedly in May 2001.
We would like to thank the staff of the Office of the Chief Medical Examiner, Carl Soderstrom, MD, of the National Study Center for Trauma and EMS for their assistance on this project.
Human Participant Protection
Study protocols were approved by the institutional review board of the University of Maryland, Baltimore (IRB no. 0101317).
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Footnotes |
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K. M. Auman assisted with the study plan, reviewed the autopsy reports, entered and analyzed the data, and contributed to the writing of the article. J. A. Kufera assisted with the study plan, planned the analysis, and contributed to the writing of the article. M. F. Ballesteros reviewed the literature and contributed to the writing of the article. J. E. Smialek provided access to the autopsy reports and reviewed the article. P. C. Dischinger designed the study, planned the analysis, and reviewed the article.
Accepted for publication July 5, 2001.
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References |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSReferences |
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1. National Highway Traffic Safety Administration. Traffic Safety Facts 1998: Motorcycles. Washington, DC: US Dept of Transportation; 1998.
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