Cycling-related crash risk and the role of cannabis and alcohol: a case-crossover study

Asbridge, Mark; Mann, Robert B.; Cusimano, Michael D.; Tallon, John M.; Pauley, Chris; Rehm, Jürgen · 2014 · OpenAlex-citations

DOI: 10.1016/j.ypmed.2014.06.006

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Summary

This study investigates whether acute consumption of cannabis and alcohol increases the risk of non-fatal cycling crashes. Motivated by established evidence linking these substances to motor vehicle crash risk and a lack of data regarding cyclists, the research aims to quantify prevalence and risk associations in a population where legislative changes regarding cannabis are likely to increase usage. The study addresses a critical gap in road safety literature, as few prior studies have examined cannabis prevalence among injured cyclists or its specific impact on crash risk. The researchers employed a case-crossover design, recruiting 393 non-fatally injured cyclists from three Canadian emergency departments between April 2009 and July 2011. In this design, each participant serves as their own control, comparing substance exposure during the six hours preceding the crash (case period) against two control periods: the last time the cyclist rode around the same time of day, and their typical usage frequency over the preceding six months. Exposure was assessed via blood samples (measuring THC and ethanol levels) or self-report. Conditional fixed effects logistic regression models were used to estimate crash risk, isolating the effects of cannabis and alcohol by excluding participants who used other substances like benzodiazepines or cocaine in specific models. The results indicated that approximately 15% of cyclists reported using cannabis and 14.5% reported using alcohol prior to their crash; blood testing revealed higher prevalence rates of 28.8% for cannabis and 21.6% for alcohol. Alcohol use was consistently associated with a significantly increased crash risk, with an odds ratio (OR) of 4.00 (95% CI: 1.64–9.78) when measured by blood or self-report. In contrast, findings for cannabis were inconsistent and dependent on measurement method. When cannabis use was identified by blood testing or self-report in the case period, the OR was 2.38 (95% CI: 1.04–5.43). However, when relying solely on self-report for both case and control periods, the association was non-significant (OR 0.40; 95% CI: 0.12–1.27). The authors attribute this discrepancy to potential under-reporting of cannabis use due to its illegal status, which biases estimates when self-report is the sole metric. The study concludes that acute alcohol consumption significantly increases the risk of cycling-related injuries, supporting the need for stricter regulations and public awareness campaigns. While cannabis also appears to increase risk, particularly when objectively measured, the authors caution that these findings are less definitive due to measurement inconsistencies. The research highlights a significant public health concern, noting that many injured cyclists exhibited signs of substance dependence. The authors recommend improved legislation equating penalties for impaired cycling with those for driving, alongside enhanced clinical screening and brief interventions for injured cyclists in emergency settings.

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Topics

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• cannabis
• cyclist safety
• polydrug
• illicit drugs

Information type

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• Empirical Findings: crash risk outcomes