Cycling-related crash risk and the role of cannabis and alcohol: a case-crossover study
Introduction
Psychoactive substance use poses considerable risk to cyclists (Martínez-Ruiz et al., 2013). In particular, alcohol and cannabis impair the cognitive and psychomotor skills necessary for safe cycling behavior (Crocker et al., 2010, Li et al., 2001). Alcohol has been detected in a high percentage of cyclists involved in crashes leading to injury or death (Crocker et al., 2010, Li et al., 1996, Li et al., 2001). Moreover, although evidence is limited, alcohol consumption among cyclists has been shown to increase the risk of an injury or fatal crash (Li et al., 2001, Martínez-Ruiz et al., 2013, Olkkonen and Honkanen, 1990) with a clear dose–response relationship starting at blood alcohol concentrations (BACs) of 0.02 g/dL, lower than the legal limit for driving a motor vehicle in most jurisdictions worldwide.
No studies have examined cannabis prevalence in cyclists involved in crashes, nor whether acute cannabis consumption increases bicycle crash risk. We know from data in Canada, the United States, and Europe that cannabis is the second most common substance, after alcohol, found in motor vehicle drivers injured or killed in crashes (Dussault et al., 2002, Mura et al., 2003). THC (Δ9 tetrahydrocannabinol) is the main psychoactive component in cannabis which typically produces euphoria, relaxation, as well as changes in perception, deficits in attention span and memory, and psychomotor function (Hall and Degenhardt, 2009, Kalant, 2004). Experimental and simulator studies confirm that THC produces impairment in the skills necessary for safe driving, which include unsafe driving speed, poor lane control, and increased decision and response times (Berghaus et al., 1995).
There is also strong evidence that acute cannabis use increases motor vehicle crash risk (Bogstrand et al., 2012, Laumon et al., 2005, Ramaekers et al., 2004), including two recent meta-analysis that note a doubling in the risk of crashes leading to serious injury or death (Asbridge et al., 2012, Li et al., 2012). Using data from a case-crossover study of injured cyclists presenting to emergency departments after a crash, we assess both the prevalence of alcohol and cannabis use in bicyclists involved in crashes, and determine whether acute alcohol and cannabis consumption increases the risk of a crash involving injury. This study is timely given recent legislative changes in Canada (expanding medical marijuana) and individual U.S. states, such as Colorado and Washington State (legalizing possession of small quantities of cannabis), that point to a likely increase in the prevalence of cannabis use in the general population.
Section snippets
Participants
Participants were non-fatally injured cyclists presenting to an emergency department after being involved in a traffic crash. Between April 2009 and June 2011, injured cyclists were recruited from three Canadian hospitals, capturing diverse patient populations (rural, urban, suburban, multi-ethnic, differing income and social class). The Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia, is the largest adult tertiary care hospital in Atlantic Canada and the only adult tertiary
Results
In total, 393 cyclists who presented to emergency departments in Halifax and Toronto due to a crash were included in the study. Ineligibility was due to young age, poor mental or physical competency, death, discharge or leaving without treatment, language barrier, or having a crash that occurred outside the study window, leaving us with a response rate of 73%. Of those eligible, 153 (39% of those consenting) agreed to provide a blood sample. Among all cyclists, 58 (14.8%; CI: 11.2–18.3)
Discussion
The role of substance use in bicycling related crashes is largely under-examined. While a handful of studies have noted the elevated crash risk posed by alcohol consumption (Li et al., 2001, Martínez-Ruiz et al., 2013, Olkkonen and Honkanen, 1990), no studies have looked at cannabis use among cyclists and related crash involvement. Our study offers two key findings: First, a substantial proportion of cyclists who were non-fatally injured in a crash had consumed either cannabis and/or alcohol in
Conclusion
In conclusion, our study shows that substance use in the context of cycling may pose substantial individual harm and represents an important road safety concern. Our findings on alcohol's role in cycling crashes, along with previous studies that have shown an increased risk posed to cyclists from the consumption of alcohol, may act as an impetus for policy makers to develop improved legislation directed at alcohol-impaired cycling, particularly in Canada and most of the United States where laws
Role of funding source
Funding for this research comes from an operating grant from the Canadian Institutes of Health Research (CIHR) (MOP-86584), and a grant from AUTO21 (B201-BAB), a member of the Networks of Centres of Excellence (NCE) program which is administered and funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canadian Institutes of Health Research (CIHR) and the Social Sciences and Humanities Research Council (SSHRC) of Canada, in partnership with Industry Canada.
Contributors
MA and CP did a background search of the published work. MA, RM, MC, JT, and JR designed the study, collected data, and analyzed and interpreted data. MA and CP wrote the first draft. All authors revised the report.
Conflicts of interest
We declare that we have no conflicts of interest. This manuscript is an honest, accurate, and transparent account of the study being reported. No important aspects of the study have been omitted.
Acknowledgements
We would like to thank Dr. Rakesh Kumar and Dr. Kirk Magee for their contributions to the project. We wish to thank Esther Giesbrecht and the Clinical Laboratory Team at the Centre for Addiction and Mental Health for the analysis of blood samples. We also wish to thank Dr. Andreas Laupacis and Dr. Joel Ray for helpful comments on earlier drafts of the manuscript.
References (30)
- et al.
Alcohol, bicycling, and head and brain injury: a study of impaired cyclists' riding patterns
Am. J. Emerg. Med.
(2010) - et al.
Adverse health effects of non-medical cannabis use
Lancet
(2009) Adverse effects of cannabis on health: an update of the literature since 1996
Prog. Neuropsychopharmacol. Biol. Psychiatry
(2004)- et al.
Risk factors for causing road crashes involving cyclists: an application of a quasi-induced exposure method
Accid. Anal. Prev.
(2013) - et al.
Alcohol, drugs and impairment in fatal traffic accidents in British Columbia
Accid. Anal. Prev.
(1995) - et al.
Comparison of the prevalence of alcohol, cannabis and other drugs between 900 injured drivers and 900 control subjects: results of a French collaborative study
Forensic Sci. Int.
(2003) - et al.
The role of alcohol in nonfatal bicycle injuries
Accid. Anal. Prev.
(1990) - et al.
Dose-related risk of motor vehicle crashes after cannabis use
Drug Alcohol Depend.
(2004) - et al.
Marijuana and other drug use among automobile and motorcycle drivers treated at a trauma center
Accid. Anal. Prev.
(1995) - et al.
Alcohol and drug use among motor vehicle collision victims admitted to a regional trauma unit: demographic, injury, and crash characteristic
Accid. Anal. Prev.
(1993)