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Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes a
b
c
a
a
Matthew E. Rossheim , Fernando Wilson , Sumihiro Suzuki , Mayra Rodriguez , Scott Walters a
& Dennis L. Thombs a
Department of Behavioral and Community Health, University of North Texas Health Science Center, Fort Worth, Texas b
University of Nebraska Medical Center, Department of Health Services Research & Administration, Omaha, Nebraska c
Click for updates
Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas Accepted author version posted online: 18 Nov 2013.Published online: 12 Jun 2014.
To cite this article: Matthew E. Rossheim, Fernando Wilson, Sumihiro Suzuki, Mayra Rodriguez, Scott Walters & Dennis L. Thombs (2014) Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes, Traffic Injury Prevention, 15:7, 678-684, DOI: 10.1080/15389588.2013.866235 To link to this article: http://dx.doi.org/10.1080/15389588.2013.866235
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Traffic Injury Prevention (2014) 15, 678–684 C Taylor & Francis Group, LLC Copyright ISSN: 1538-9588 print / 1538-957X online DOI: 10.1080/15389588.2013.866235
Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes MATTHEW E. ROSSHEIM1, FERNANDO WILSON2, SUMIHIRO SUZUKI3, MAYRA RODRIGUEZ1, SCOTT WALTERS1, and DENNIS L. THOMBS1 1
Department of Behavioral and Community Health, University of North Texas Health Science Center, Fort Worth, Texas University of Nebraska Medical Center, Department of Health Services Research & Administration, Omaha, Nebraska 3 Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas 2
Downloaded by [Loughborough University] at 09:23 10 December 2014
Received 5 July 2013, Accepted 12 November 2013
Objective: Helmet use reduces mortality risk for motorcyclists, regardless of drug and alcohol use. However, the association between drug use and motorcycle helmet utilization is not well known. This study examines the relationship between drug use and motorcycle helmet use among fatally injured motorcycle riders. Methods: Using data from the 2005–2009 Fatality Analysis Reporting System (FARS), we examined the association between drug use and motorcycle helmet use in a multivariable logistic regression analysis of 9861 fatally injured motorcycle riders in the United States. Results: For fatally injured motorcycle riders, use of alcohol, marijuana, or other drugs was associated with increased odds of not wearing a motorcycle helmet, controlling for the effects of state motorcycle helmet laws and other confounding variables. Predicted probabilities indicate that helmet use substantially decreases among fatally injured riders mixing alcohol with marijuana and other drugs. Furthermore, the likelihood of helmet use between marijuana-only users and other drug users is virtually the same across all blood alcohol content (BAC) levels. Conclusions: This study provides evidence that alcohol, marijuana, and other drug use is associated with not wearing a motorcycle helmet in fatal motorcycle crashes. There is a clear need for additional prevention and intervention efforts that seek to change helmet and drug use norms among motorcycle riders. Keywords: motorcycles, helmets, marijuana, drugs, alcohol drinking
Introduction In 2007, motorcyclists were nearly 37 times more likely to die in a traffic crash compared to passenger car occupants per mile driven (NHTSA 2008). For motorcycle riders, helmet use reduces the risk of injury and death (Schneider et al. 2011). Recent meta-analyses reported that helmet use reduced risk of head injury and death in motorcycle riders who crash by 69 and 42 percent, respectively (Liu et al. 2008). The NHTSA estimates that 1544 lives were saved from motorcycle helmet use in 2010 and that an additional 709 lives would have been saved that year if all motorcyclists had worn helmets (Centers for Disease Control and Prevention 2012). Along with preventing death and disability, using motorcycle helmets helps reduce the economic burden of motorcycle crashes. The U.S. Department of Transportation estimated in 2008 that $2.9 billion in injury-related costs was saved due to helmet use, and Managing Editor David Viano oversaw the review of this article. Address correspondence to Matthew E. Rossheim, University of North Texas Health Science Center, Department of Behavioral and Community Health, 3500 Camp Bowie Blvd., Fort Worth, TX 76107. E-mail: [email protected]
an additional $1.3 billion would have been saved if all motorcyclists had worn helmets (NHTSA 2011). Laws mandating motorcycle helmet use have been effective in both increasing use of motorcycle helmets and reducing related fatalities (Houston and Richardson 2007; Mayrose 2008; Muller 2004; NHTSA 2009; Sass and Zimmerman 2000). Although the majority of states required all motorcyclists to wear helmets at one point in time, currently most states only require helmets for individuals under a state-specific age. In 1967, the U.S. government began requiring states to enact motorcycle helmet laws to qualify for federal transportation funds. By 1975, 47 states had universal helmet laws; that is, laws requiring all motorcyclists to use a helmet, regardless of their age (Governors Highway Safety Association [GHSA] 2013; Insurance Institute for Highway Safety [IIHS] 2013). However, starting in the late 1970s, several states repealed or weakened their motorcycle helmet laws, claiming that motorcyclists’ rights were being violated (Curtin 1996; GHSA 2013; IIHS 2013). Currently, only 19 states and the District of Columbia have universal helmet laws (GHSA 2013). Twenty-eight states have partial helmet laws, which vary by state; however, the most common partial helmet law only requires motorcyclists younger than 18 years old to wear a helmet (GHSA 2013).
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Drug Use and Motorcycle Helmet Use In addition to the penalties associated with helmet laws, substance use might affect people’s decision to wear a helmet. Research suggests that users of alcohol and other drugs are less likely to utilize traffic safety equipment, such as seat belts or helmets (Everett et al. 1999; Pulido et al. 2011). However, these studies rely on retrospective self-report of both behaviors. In 2011, Romano and Voas published a report using data from the Fatality Analysis Reporting System (FARS)—a census of all fatal traffic crashes in the United States—to examine drug use among drivers involved in fatal crashes. They found, after controlling for covariates such as age and sex, the use of alcohol, marijuana, and other drugs was associated with reduced odds of seatbelt use (Romano and Voas 2011). Although there is a lack of research regarding the association between motorcycle helmet use and marijuana and other drug use, there is some evidence that alcohol use is a risk factor for not wearing a motorcycle helmet (Brown et al. 2011; Hingson and Winter 2003; Ouellet 2011; Pickrell and Starnes 2008). For example, one study of 1738 trauma patients involved in motorcycle crashes identified a 3-fold risk of not wearing a helmet for patients with a positive blood alcohol content (BAC; Brown et al. 2011). Another study utilizing the FARS data found that alcohol intoxication was associated with reduced odds of helmet use among fatally injured riders (Pickrell and Starnes 2008). Though some studies have examined the association between alcohol intoxication and motorcycle helmet use, there are few, if any, studies examining the relationship between marijuana and other drug use and utilization of motorcycle helmets. Examination of the health consequences of illicit drug use is becoming increasingly important, because illicit drug use rates have risen in recent years (National Institute on Drug Abuse 2012). Specifically, past month marijuana use among Americans 12 years or older is estimated to have increased from 5.8 percent in 2007 to 7.0 percent in 2011 (National Institute on Drug Abuse 2014). To our knowledge, this study is the first to examine the association between marijuana and other drug use and motorcycle helmet use among riders fatally injured in crashes. We hypothesized that, among fatally injured motorcycle riders, use of marijuana and/or other drugs is associated with reduced odds of motorcycle helmet use, after adjusting for the effects of motorcycle helmet laws, alcohol use, and other potentially confounding variables.
Methods Data The FARS database is a census of all traffic crashes on public roads in the United States resulting in a fatality within 30 days of the crash. FARS is compiled by the NHTSA and includes detailed information on each crash, vehicle, and victim using reports from crash scene investigators, emergency medical services, coroners, hospital providers, and other authoritative sources. Additional information on FARS is provided elsewhere (http://wwwnrd.nhtsa.dot.gov/Pubs/FARSBrochure.pdf).
679 Inclusion Criteria Analyses were restricted to fatally injured motorcycle riders (the persons in control of the motorcycle) ages 21 and older with non-missing information on (1) helmet use, (2) drug use, (3) blood alcohol content, (4) state within which the crash took place, (5) time of crash, (6) motorcycle license status, and (7) the riders’ age, sex, race, and ethnicity. After removing individuals who did not meet the criteria, 9789 cases (48%) remained for analyses. Approximately 76 percent of cases omitted were due to lack of drug and/or alcohol test data. Given the data, it was not possible to determine why some individuals were drug tested and others were not; however, cases included in analyses appear to be relatively demographically comparable to those with missing data (i.e., 96.4% versus 96.5% male, 79.3% versus 82.0% non-Hispanic white). For more details see the Appendix (see online supplement). The largest proportional differences between those included in analyses and those not included in analyses were whether the crash was in a state with a universal helmet law (47.5% versus 40.1%) and whether the individual was wearing a helmet (63.2% versus 56.0%). The most plausible explanation for this observation is that agencies in states with universal helmet laws more routinely drug test fatally injured motorcycle riders, and universal helmet laws are strongly predictive of whether or not riders wear helmets. Measures Drug and Alcohol Use FARS data include results from drug and alcohol testing, if performed. Drug use data include toxicology results from blood and/or urine tests for motorcyclists suspected of drug use by police investigators. Individuals were coded as using marijuana if test results were positive for any cannabinoid variants. Individuals were coded as using “other” drugs if they tested positive for any other (non-marijuana, non-alcohol) known drugs; that is, narcotics, depressants, stimulants, hallucinogens, phencyclidine, anabolic steroids, and/or inhalants. If the rider’s BAC (measured in grams per deciliter) was tested, this value was used. Although approximately 60 percent of overall cases in the FARS database are missing BAC data, only 1 percent (101/9789) of study observations were missing BAC data, because individuals who were tested for drugs were likely to also be tested for alcohol. Motorcycle Helmet Use and Laws Motorcycle helmet nonuse was coded 0 if the rider was wearing a motorcycle helmet or 1 if the rider was not wearing a motorcycle helmet. Individuals with unknown helmet use and those who used a motorcycle helmet “improperly” as recorded by police accident reports were removed from analyses (4.2% of cases). Information on motorcycle helmet laws were gathered from the IIHS (2013) and corroborated with the GHSA (2013). Although 19 states currently have universal helmet laws, Michigan repealed their universal helmet law in 2012 (GHSA 2013). Therefore, 20 states had universal helmet laws from 2005 to 2009 (GHSA 2013; Mayrose 2008). In our analyses, if the fatal crash occurred in a state with a universal helmet
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law, motorcycle riders were coded as legally obligated to wear a helmet. In states without universal helmet laws, individuals under the age of 21 years old might or might not be legally required to wear a helmet depending on state law, their age, or other state-specific exemptions (such as being licensed for a given period of time or having a minimum amount of medical coverage). Therefore, individuals under the age of 21 were removed from analyses to provide consistency across states in helmet use policies. A dichotomous variable was defined for whether a crash occurred in a state requiring helmet use for all riders or not. Confounding Variables Possible confounders included both individual-level (i.e., age, sex, race/ethnicity, properly licensed for operating motorcycles) and crash-level (i.e., year, region, accident at night versus during the day) variables. Regions were coded according to the U.S. Census Bureau to account for regional differences in helmet use, and dichotomous variables were defined for each year in the study period. A dichotomous variable was defined if the crash occurred at nighttime (6:00 p.m. to 5:59 a.m.) versus during the daytime (6:00 a.m. to 5:59 p.m.), because among fatally injured motorcycle riders, helmet use is less frequent at night compared to during the day (Pickrell and Starnes 2008). Analytical Plan Univariate statistics on the distribution of marijuana and other drug use are calculated comparing fatally injured riders with and without helmets. Afterward, multivariable logistic regression analyses were used to predict the odds of helmet use from alcohol, marijuana, and other drug use, adjusting for existence of a state universal helmet law, age, sex, race/ethnicity, motorcycle license status, time of day, region, and year. All motorcycle rider fatalities age 21 and older with non-missing data in 2005–2009 were examined. Statistical power was sufficiently large for statistical validity (Peduzi et al. 1996). STATA 12 (StataCorp, College Station, TX) was used for all analyses.
Results Descriptive Statistics From 2005 to 2009, motorcycles represented only 6.4 percent of all vehicles involved in fatal traffic crashes in the United States, yet they accounted for 13.7 percent of individuals fatally injured in vehicular crashes. Approximately 40 percent of fatally injured motorcycle riders were not wearing a motorcycle helmet. In our sample of fatally injured motorcycle operators 21 and older with non-missing data, the majority were non-Hispanic white (79.3%) and/or male (96.4%). Among fatally injured motorcycle riders 21 and older, 38.1 percent tested positive for alcohol, 10.3 percent tested positive for marijuana, and 19.5 percent tested positive for other drugs. More than 2 out of 5 marijuana users and other drug users also tested positive for alcohol. Approximately 1.2 percent of fatally injured motorcycle riders tested positive for all 3: alcohol, marijuana, and other drugs.
Rossheim et al. Motorcycle Helmet Use and Drug/Alcohol Use Table 1 provides descriptive statistics for fatally injured motorcycle riders by helmet use. Users of alcohol, marijuana, and other drugs all utilized helmets at lower rates than nonusers. The unadjusted odds ratios of motorcycle helmet nonuse for those who tested positive for marijuana and other, nonmarijuana drugs are 1.11 and 1.58, respectively. Past studies have found that motorcycle helmet laws strongly influence helmet utilization (Mayrose 2008; Pickrell and Starnes 2008). Therefore, Table 2 was constructed to show the association between drug use and helmet use, accounting for state motorcycle helmet laws (universal, partial, and no helmet law). As can be seen, after stratifying by helmet laws, fatally injured riders who did not wear helmets had a higher prevalence of alcohol use and were more likely to test positive for marijuana and non-marijuana drugs in combination with alcohol than their helmet wearing counterparts. In multivariable analyses, use of alcohol, marijuana, and other drugs was independently associated with increased odds of not wearing a motorcycle helmet after adjusting for confounding factors. Table 3 shows that fatally injured marijuana or other drug users had approximately 25 percent increased odds of not having worn a motorcycle helmet or 50 percent increased odds if they tested positive for both marijuana and non-marijuana drugs. The existence of state universal helmet laws was associated with a 20-fold increase in the odds of wearing a helmet. Older age of the rider and not being licensed to operate a motorcycle were associated with reduced odds of helmet use, but sex, race/ethnicity, and time of day were not statistically significant. To address a potential bias related to unavailable drug test results, we conducted additional analyses subselecting only individuals in those states that had consistent drug testing policies. Table 4 provides results from a logistic regression analysis performed for only those states that drug tested more than one-half of fatally injured motorcycle riders. This subsample consists of data from 15 fewer states (i.e., Alabama, Arkansas, Delaware, Idaho, Iowa, Kansas, Maine, Mississippi, Nebraska, Oklahoma, Oregon, South Dakota, Texas, Utah, and Vermont) but still includes nearly 9000 cases and yields results comparable to the original regression model. To further examine the relationship between drug and helmet use across different BAC levels, predicted probabilities were calculated and graphed (Figure 1). Helmet use substantially decreases among motorcyclists mixing alcohol with marijuana and other drugs. However, the likelihood of helmet use between marijuana-only users and other drug users is virtually the same across all BAC levels.
Discussion To our knowledge, this is the first study to examine the relationship between drug use (other than alcohol) and motorcycle helmet use using a census of all fatal crashes in the United States. Our event-level findings suggest that, among fatally injured motorcycle riders, use of marijuana and other drugs was independently associated with increased odds of not wearing a helmet, even after accounting for state helmet
Drug Use and Motorcycle Helmet Use
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Table 1. Descriptive statistics for fatally injured motorcycle riders by helmet use (N = 9789) Toxicology results No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only Blood alcohol concentration Blood alcohol concentration among riders with positive BACs Demographics Male Age in years White non-Hispanic Hispanic Black non-Hispanic Other race/ethnicity Not properly licensed Crash characteristics Nighttime (6:00 p.m.–5:59 a.m.)
Used helmet (N = 6185)
Did not use helmet (N = 3604)
P value of χ 2 or t test
3322 (53.7%) 1376 (22.2%) 571 (9.2%)
1250 (34.7%) 1214 (33.7%) 357 (9.9%)
P < .001 P < .001 ns
275 (4.4%) 175 (2.8%) 305 (4.9%)
127 (3.5%) 143 (4.0%) 391 (10.8%)
P < .03 P < .01 P < .001
μ = 0.042 (SD = 0.077) μ = 0.136 (SD = 0.080)
μ = 0.076 (SD = 0.093) μ = 0.150 (SD = 0.078)
P < .001 P < .001
5945 (96.1%) μ = 39.65 (SD = 13.46) 4753 (76.8%) 523 (8.5%) 718 (11.6%) 191 (3.1%) 1448 (23.4%)
3488 (96.8%) μ = 41.70 (SD = 12.34) 3014 (83.6%) 260 (7.2%) 282 (7.8%) 48 (1.3%) 874 (24.3%)
ns P < .001 P < .001 P < .03 P < .001 P < .001 ns
2859 (46.2%)
1993(55.3%)
P < .001
Table 2. Association of drug use and helmet use by state motorcycle helmet laws (N = 9789)a Universal helmet law (n = 4654) No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs Partial helmet law (n = 4631)b No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs No helmet law (n = 504) No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs aNot
Used helmet
Did not use helmet
P value of χ 2 or t test
(N = 4308) 2270 (52.7%) 1,028 (23.9%) 351 (8.1%)
(N = 346) 123 (35.5%) 114 (32.9%) 22 (6.4%)
P < .001 P < .001 ns
202 (4.7%) 130 (3.0%) 206 (4.8%)
22 (6.4%) 16 (4.6%) 36 (10.4%)
ns ns P < .001
μ = 0.138 (SD = 0.078)
μ = 0.146 (SD = 0.075)
ns
(N = 1769) 977 (55.2%) 331 (18.7%) 216 (12.2%)
(N = 2862) 976 (34.1%) 968 (33.8%) 318 (11.1%)
P < .001 P < .001 ns
70 (4.0%) 44 (2.5%) 92 (5.2%)
91 (3.2%) 101 (3.5%) 321 (11.2%)
ns P < .05 P < .001
μ = 0.128 (SD = 0.082)
μ = 0.152 (SD = 0.079)
P < .001
(N = 108) 75 (69.4%) 17 (15.7%) 4 (3.7%)
(N = 396) 151 (38.1%) 132 (33.3%) 17 (4.3%)
P < .001 P < .001 ns
3 (2.8%) 1 (0.9%) 7 (6.5%)
14 (3.5%) 26 (6.6%) 34 (8.6%)
ns ns ns
μ = 0.143 (SD = 0.093)
μ = 0.140 (SD = 0.077)
ns
all drug use groups are shown due to the small number of cases in cells (i.e., marijuana and non-marijuana drugs use without alcohol and marijuana, non-marijuana, and alcohol use). bPartial helmet laws indicate that individuals under a certain minimum age threshold are required to wear a helmet, but in our sample, all individuals were over this threshold. Therefore, for states with partial helmet laws and those with no helmet law, individuals in this sample were not legally obliged to wear a helmet. In states with universal helmet laws, all riders are legally obliged to wear a helmet.
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Rossheim et al.
Table 3. Multivariable logistic regression model of variables associated with helmet nonuse among fatally injured motorcycle riders ≥21 years old (N = 9789)a,b Variable
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Helmet use not required for all riders by law Tested positive for marijuana and non-marijuana drugs Tested positive for marijuana only Tested positive for non-marijuana drugs only BAC BAC squared Not properly licensed Age (in years)
Adjusted odds ratio
95% Confidence interval
P value
19.8
17.0–23.1
Traffic Injury Prevention Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gcpi20
Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes a
b
c
a
a
Matthew E. Rossheim , Fernando Wilson , Sumihiro Suzuki , Mayra Rodriguez , Scott Walters a
& Dennis L. Thombs a
Department of Behavioral and Community Health, University of North Texas Health Science Center, Fort Worth, Texas b
University of Nebraska Medical Center, Department of Health Services Research & Administration, Omaha, Nebraska c
Click for updates
Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas Accepted author version posted online: 18 Nov 2013.Published online: 12 Jun 2014.
To cite this article: Matthew E. Rossheim, Fernando Wilson, Sumihiro Suzuki, Mayra Rodriguez, Scott Walters & Dennis L. Thombs (2014) Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes, Traffic Injury Prevention, 15:7, 678-684, DOI: 10.1080/15389588.2013.866235 To link to this article: http://dx.doi.org/10.1080/15389588.2013.866235
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Traffic Injury Prevention (2014) 15, 678–684 C Taylor & Francis Group, LLC Copyright ISSN: 1538-9588 print / 1538-957X online DOI: 10.1080/15389588.2013.866235
Associations Between Drug Use and Motorcycle Helmet Use in Fatal Crashes MATTHEW E. ROSSHEIM1, FERNANDO WILSON2, SUMIHIRO SUZUKI3, MAYRA RODRIGUEZ1, SCOTT WALTERS1, and DENNIS L. THOMBS1 1
Department of Behavioral and Community Health, University of North Texas Health Science Center, Fort Worth, Texas University of Nebraska Medical Center, Department of Health Services Research & Administration, Omaha, Nebraska 3 Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas 2
Downloaded by [Loughborough University] at 09:23 10 December 2014
Received 5 July 2013, Accepted 12 November 2013
Objective: Helmet use reduces mortality risk for motorcyclists, regardless of drug and alcohol use. However, the association between drug use and motorcycle helmet utilization is not well known. This study examines the relationship between drug use and motorcycle helmet use among fatally injured motorcycle riders. Methods: Using data from the 2005–2009 Fatality Analysis Reporting System (FARS), we examined the association between drug use and motorcycle helmet use in a multivariable logistic regression analysis of 9861 fatally injured motorcycle riders in the United States. Results: For fatally injured motorcycle riders, use of alcohol, marijuana, or other drugs was associated with increased odds of not wearing a motorcycle helmet, controlling for the effects of state motorcycle helmet laws and other confounding variables. Predicted probabilities indicate that helmet use substantially decreases among fatally injured riders mixing alcohol with marijuana and other drugs. Furthermore, the likelihood of helmet use between marijuana-only users and other drug users is virtually the same across all blood alcohol content (BAC) levels. Conclusions: This study provides evidence that alcohol, marijuana, and other drug use is associated with not wearing a motorcycle helmet in fatal motorcycle crashes. There is a clear need for additional prevention and intervention efforts that seek to change helmet and drug use norms among motorcycle riders. Keywords: motorcycles, helmets, marijuana, drugs, alcohol drinking
Introduction In 2007, motorcyclists were nearly 37 times more likely to die in a traffic crash compared to passenger car occupants per mile driven (NHTSA 2008). For motorcycle riders, helmet use reduces the risk of injury and death (Schneider et al. 2011). Recent meta-analyses reported that helmet use reduced risk of head injury and death in motorcycle riders who crash by 69 and 42 percent, respectively (Liu et al. 2008). The NHTSA estimates that 1544 lives were saved from motorcycle helmet use in 2010 and that an additional 709 lives would have been saved that year if all motorcyclists had worn helmets (Centers for Disease Control and Prevention 2012). Along with preventing death and disability, using motorcycle helmets helps reduce the economic burden of motorcycle crashes. The U.S. Department of Transportation estimated in 2008 that $2.9 billion in injury-related costs was saved due to helmet use, and Managing Editor David Viano oversaw the review of this article. Address correspondence to Matthew E. Rossheim, University of North Texas Health Science Center, Department of Behavioral and Community Health, 3500 Camp Bowie Blvd., Fort Worth, TX 76107. E-mail: [email protected]
an additional $1.3 billion would have been saved if all motorcyclists had worn helmets (NHTSA 2011). Laws mandating motorcycle helmet use have been effective in both increasing use of motorcycle helmets and reducing related fatalities (Houston and Richardson 2007; Mayrose 2008; Muller 2004; NHTSA 2009; Sass and Zimmerman 2000). Although the majority of states required all motorcyclists to wear helmets at one point in time, currently most states only require helmets for individuals under a state-specific age. In 1967, the U.S. government began requiring states to enact motorcycle helmet laws to qualify for federal transportation funds. By 1975, 47 states had universal helmet laws; that is, laws requiring all motorcyclists to use a helmet, regardless of their age (Governors Highway Safety Association [GHSA] 2013; Insurance Institute for Highway Safety [IIHS] 2013). However, starting in the late 1970s, several states repealed or weakened their motorcycle helmet laws, claiming that motorcyclists’ rights were being violated (Curtin 1996; GHSA 2013; IIHS 2013). Currently, only 19 states and the District of Columbia have universal helmet laws (GHSA 2013). Twenty-eight states have partial helmet laws, which vary by state; however, the most common partial helmet law only requires motorcyclists younger than 18 years old to wear a helmet (GHSA 2013).
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Drug Use and Motorcycle Helmet Use In addition to the penalties associated with helmet laws, substance use might affect people’s decision to wear a helmet. Research suggests that users of alcohol and other drugs are less likely to utilize traffic safety equipment, such as seat belts or helmets (Everett et al. 1999; Pulido et al. 2011). However, these studies rely on retrospective self-report of both behaviors. In 2011, Romano and Voas published a report using data from the Fatality Analysis Reporting System (FARS)—a census of all fatal traffic crashes in the United States—to examine drug use among drivers involved in fatal crashes. They found, after controlling for covariates such as age and sex, the use of alcohol, marijuana, and other drugs was associated with reduced odds of seatbelt use (Romano and Voas 2011). Although there is a lack of research regarding the association between motorcycle helmet use and marijuana and other drug use, there is some evidence that alcohol use is a risk factor for not wearing a motorcycle helmet (Brown et al. 2011; Hingson and Winter 2003; Ouellet 2011; Pickrell and Starnes 2008). For example, one study of 1738 trauma patients involved in motorcycle crashes identified a 3-fold risk of not wearing a helmet for patients with a positive blood alcohol content (BAC; Brown et al. 2011). Another study utilizing the FARS data found that alcohol intoxication was associated with reduced odds of helmet use among fatally injured riders (Pickrell and Starnes 2008). Though some studies have examined the association between alcohol intoxication and motorcycle helmet use, there are few, if any, studies examining the relationship between marijuana and other drug use and utilization of motorcycle helmets. Examination of the health consequences of illicit drug use is becoming increasingly important, because illicit drug use rates have risen in recent years (National Institute on Drug Abuse 2012). Specifically, past month marijuana use among Americans 12 years or older is estimated to have increased from 5.8 percent in 2007 to 7.0 percent in 2011 (National Institute on Drug Abuse 2014). To our knowledge, this study is the first to examine the association between marijuana and other drug use and motorcycle helmet use among riders fatally injured in crashes. We hypothesized that, among fatally injured motorcycle riders, use of marijuana and/or other drugs is associated with reduced odds of motorcycle helmet use, after adjusting for the effects of motorcycle helmet laws, alcohol use, and other potentially confounding variables.
Methods Data The FARS database is a census of all traffic crashes on public roads in the United States resulting in a fatality within 30 days of the crash. FARS is compiled by the NHTSA and includes detailed information on each crash, vehicle, and victim using reports from crash scene investigators, emergency medical services, coroners, hospital providers, and other authoritative sources. Additional information on FARS is provided elsewhere (http://wwwnrd.nhtsa.dot.gov/Pubs/FARSBrochure.pdf).
679 Inclusion Criteria Analyses were restricted to fatally injured motorcycle riders (the persons in control of the motorcycle) ages 21 and older with non-missing information on (1) helmet use, (2) drug use, (3) blood alcohol content, (4) state within which the crash took place, (5) time of crash, (6) motorcycle license status, and (7) the riders’ age, sex, race, and ethnicity. After removing individuals who did not meet the criteria, 9789 cases (48%) remained for analyses. Approximately 76 percent of cases omitted were due to lack of drug and/or alcohol test data. Given the data, it was not possible to determine why some individuals were drug tested and others were not; however, cases included in analyses appear to be relatively demographically comparable to those with missing data (i.e., 96.4% versus 96.5% male, 79.3% versus 82.0% non-Hispanic white). For more details see the Appendix (see online supplement). The largest proportional differences between those included in analyses and those not included in analyses were whether the crash was in a state with a universal helmet law (47.5% versus 40.1%) and whether the individual was wearing a helmet (63.2% versus 56.0%). The most plausible explanation for this observation is that agencies in states with universal helmet laws more routinely drug test fatally injured motorcycle riders, and universal helmet laws are strongly predictive of whether or not riders wear helmets. Measures Drug and Alcohol Use FARS data include results from drug and alcohol testing, if performed. Drug use data include toxicology results from blood and/or urine tests for motorcyclists suspected of drug use by police investigators. Individuals were coded as using marijuana if test results were positive for any cannabinoid variants. Individuals were coded as using “other” drugs if they tested positive for any other (non-marijuana, non-alcohol) known drugs; that is, narcotics, depressants, stimulants, hallucinogens, phencyclidine, anabolic steroids, and/or inhalants. If the rider’s BAC (measured in grams per deciliter) was tested, this value was used. Although approximately 60 percent of overall cases in the FARS database are missing BAC data, only 1 percent (101/9789) of study observations were missing BAC data, because individuals who were tested for drugs were likely to also be tested for alcohol. Motorcycle Helmet Use and Laws Motorcycle helmet nonuse was coded 0 if the rider was wearing a motorcycle helmet or 1 if the rider was not wearing a motorcycle helmet. Individuals with unknown helmet use and those who used a motorcycle helmet “improperly” as recorded by police accident reports were removed from analyses (4.2% of cases). Information on motorcycle helmet laws were gathered from the IIHS (2013) and corroborated with the GHSA (2013). Although 19 states currently have universal helmet laws, Michigan repealed their universal helmet law in 2012 (GHSA 2013). Therefore, 20 states had universal helmet laws from 2005 to 2009 (GHSA 2013; Mayrose 2008). In our analyses, if the fatal crash occurred in a state with a universal helmet
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law, motorcycle riders were coded as legally obligated to wear a helmet. In states without universal helmet laws, individuals under the age of 21 years old might or might not be legally required to wear a helmet depending on state law, their age, or other state-specific exemptions (such as being licensed for a given period of time or having a minimum amount of medical coverage). Therefore, individuals under the age of 21 were removed from analyses to provide consistency across states in helmet use policies. A dichotomous variable was defined for whether a crash occurred in a state requiring helmet use for all riders or not. Confounding Variables Possible confounders included both individual-level (i.e., age, sex, race/ethnicity, properly licensed for operating motorcycles) and crash-level (i.e., year, region, accident at night versus during the day) variables. Regions were coded according to the U.S. Census Bureau to account for regional differences in helmet use, and dichotomous variables were defined for each year in the study period. A dichotomous variable was defined if the crash occurred at nighttime (6:00 p.m. to 5:59 a.m.) versus during the daytime (6:00 a.m. to 5:59 p.m.), because among fatally injured motorcycle riders, helmet use is less frequent at night compared to during the day (Pickrell and Starnes 2008). Analytical Plan Univariate statistics on the distribution of marijuana and other drug use are calculated comparing fatally injured riders with and without helmets. Afterward, multivariable logistic regression analyses were used to predict the odds of helmet use from alcohol, marijuana, and other drug use, adjusting for existence of a state universal helmet law, age, sex, race/ethnicity, motorcycle license status, time of day, region, and year. All motorcycle rider fatalities age 21 and older with non-missing data in 2005–2009 were examined. Statistical power was sufficiently large for statistical validity (Peduzi et al. 1996). STATA 12 (StataCorp, College Station, TX) was used for all analyses.
Results Descriptive Statistics From 2005 to 2009, motorcycles represented only 6.4 percent of all vehicles involved in fatal traffic crashes in the United States, yet they accounted for 13.7 percent of individuals fatally injured in vehicular crashes. Approximately 40 percent of fatally injured motorcycle riders were not wearing a motorcycle helmet. In our sample of fatally injured motorcycle operators 21 and older with non-missing data, the majority were non-Hispanic white (79.3%) and/or male (96.4%). Among fatally injured motorcycle riders 21 and older, 38.1 percent tested positive for alcohol, 10.3 percent tested positive for marijuana, and 19.5 percent tested positive for other drugs. More than 2 out of 5 marijuana users and other drug users also tested positive for alcohol. Approximately 1.2 percent of fatally injured motorcycle riders tested positive for all 3: alcohol, marijuana, and other drugs.
Rossheim et al. Motorcycle Helmet Use and Drug/Alcohol Use Table 1 provides descriptive statistics for fatally injured motorcycle riders by helmet use. Users of alcohol, marijuana, and other drugs all utilized helmets at lower rates than nonusers. The unadjusted odds ratios of motorcycle helmet nonuse for those who tested positive for marijuana and other, nonmarijuana drugs are 1.11 and 1.58, respectively. Past studies have found that motorcycle helmet laws strongly influence helmet utilization (Mayrose 2008; Pickrell and Starnes 2008). Therefore, Table 2 was constructed to show the association between drug use and helmet use, accounting for state motorcycle helmet laws (universal, partial, and no helmet law). As can be seen, after stratifying by helmet laws, fatally injured riders who did not wear helmets had a higher prevalence of alcohol use and were more likely to test positive for marijuana and non-marijuana drugs in combination with alcohol than their helmet wearing counterparts. In multivariable analyses, use of alcohol, marijuana, and other drugs was independently associated with increased odds of not wearing a motorcycle helmet after adjusting for confounding factors. Table 3 shows that fatally injured marijuana or other drug users had approximately 25 percent increased odds of not having worn a motorcycle helmet or 50 percent increased odds if they tested positive for both marijuana and non-marijuana drugs. The existence of state universal helmet laws was associated with a 20-fold increase in the odds of wearing a helmet. Older age of the rider and not being licensed to operate a motorcycle were associated with reduced odds of helmet use, but sex, race/ethnicity, and time of day were not statistically significant. To address a potential bias related to unavailable drug test results, we conducted additional analyses subselecting only individuals in those states that had consistent drug testing policies. Table 4 provides results from a logistic regression analysis performed for only those states that drug tested more than one-half of fatally injured motorcycle riders. This subsample consists of data from 15 fewer states (i.e., Alabama, Arkansas, Delaware, Idaho, Iowa, Kansas, Maine, Mississippi, Nebraska, Oklahoma, Oregon, South Dakota, Texas, Utah, and Vermont) but still includes nearly 9000 cases and yields results comparable to the original regression model. To further examine the relationship between drug and helmet use across different BAC levels, predicted probabilities were calculated and graphed (Figure 1). Helmet use substantially decreases among motorcyclists mixing alcohol with marijuana and other drugs. However, the likelihood of helmet use between marijuana-only users and other drug users is virtually the same across all BAC levels.
Discussion To our knowledge, this is the first study to examine the relationship between drug use (other than alcohol) and motorcycle helmet use using a census of all fatal crashes in the United States. Our event-level findings suggest that, among fatally injured motorcycle riders, use of marijuana and other drugs was independently associated with increased odds of not wearing a helmet, even after accounting for state helmet
Drug Use and Motorcycle Helmet Use
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Table 1. Descriptive statistics for fatally injured motorcycle riders by helmet use (N = 9789) Toxicology results No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only Blood alcohol concentration Blood alcohol concentration among riders with positive BACs Demographics Male Age in years White non-Hispanic Hispanic Black non-Hispanic Other race/ethnicity Not properly licensed Crash characteristics Nighttime (6:00 p.m.–5:59 a.m.)
Used helmet (N = 6185)
Did not use helmet (N = 3604)
P value of χ 2 or t test
3322 (53.7%) 1376 (22.2%) 571 (9.2%)
1250 (34.7%) 1214 (33.7%) 357 (9.9%)
P < .001 P < .001 ns
275 (4.4%) 175 (2.8%) 305 (4.9%)
127 (3.5%) 143 (4.0%) 391 (10.8%)
P < .03 P < .01 P < .001
μ = 0.042 (SD = 0.077) μ = 0.136 (SD = 0.080)
μ = 0.076 (SD = 0.093) μ = 0.150 (SD = 0.078)
P < .001 P < .001
5945 (96.1%) μ = 39.65 (SD = 13.46) 4753 (76.8%) 523 (8.5%) 718 (11.6%) 191 (3.1%) 1448 (23.4%)
3488 (96.8%) μ = 41.70 (SD = 12.34) 3014 (83.6%) 260 (7.2%) 282 (7.8%) 48 (1.3%) 874 (24.3%)
ns P < .001 P < .001 P < .03 P < .001 P < .001 ns
2859 (46.2%)
1993(55.3%)
P < .001
Table 2. Association of drug use and helmet use by state motorcycle helmet laws (N = 9789)a Universal helmet law (n = 4654) No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs Partial helmet law (n = 4631)b No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs No helmet law (n = 504) No drugs or alcohol Used alcohol only Used other (non-marijuana) drugs only Used marijuana only Mixed alcohol with marijuana only Mixed alcohol with drugs other than marijuana only BAC among riders with positive BACs aNot
Used helmet
Did not use helmet
P value of χ 2 or t test
(N = 4308) 2270 (52.7%) 1,028 (23.9%) 351 (8.1%)
(N = 346) 123 (35.5%) 114 (32.9%) 22 (6.4%)
P < .001 P < .001 ns
202 (4.7%) 130 (3.0%) 206 (4.8%)
22 (6.4%) 16 (4.6%) 36 (10.4%)
ns ns P < .001
μ = 0.138 (SD = 0.078)
μ = 0.146 (SD = 0.075)
ns
(N = 1769) 977 (55.2%) 331 (18.7%) 216 (12.2%)
(N = 2862) 976 (34.1%) 968 (33.8%) 318 (11.1%)
P < .001 P < .001 ns
70 (4.0%) 44 (2.5%) 92 (5.2%)
91 (3.2%) 101 (3.5%) 321 (11.2%)
ns P < .05 P < .001
μ = 0.128 (SD = 0.082)
μ = 0.152 (SD = 0.079)
P < .001
(N = 108) 75 (69.4%) 17 (15.7%) 4 (3.7%)
(N = 396) 151 (38.1%) 132 (33.3%) 17 (4.3%)
P < .001 P < .001 ns
3 (2.8%) 1 (0.9%) 7 (6.5%)
14 (3.5%) 26 (6.6%) 34 (8.6%)
ns ns ns
μ = 0.143 (SD = 0.093)
μ = 0.140 (SD = 0.077)
ns
all drug use groups are shown due to the small number of cases in cells (i.e., marijuana and non-marijuana drugs use without alcohol and marijuana, non-marijuana, and alcohol use). bPartial helmet laws indicate that individuals under a certain minimum age threshold are required to wear a helmet, but in our sample, all individuals were over this threshold. Therefore, for states with partial helmet laws and those with no helmet law, individuals in this sample were not legally obliged to wear a helmet. In states with universal helmet laws, all riders are legally obliged to wear a helmet.
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Table 3. Multivariable logistic regression model of variables associated with helmet nonuse among fatally injured motorcycle riders ≥21 years old (N = 9789)a,b Variable
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Helmet use not required for all riders by law Tested positive for marijuana and non-marijuana drugs Tested positive for marijuana only Tested positive for non-marijuana drugs only BAC BAC squared Not properly licensed Age (in years)
Adjusted odds ratio
95% Confidence interval
P value
19.8
17.0–23.1
