title: Cycling-related crash risk and the role of cannabis and alcohol: a case-crossover study.
abstract: OBJECTIVE
  To examine whether alcohol and cannabis consumption increase crash risk among non-fatally injured bicyclists (N=393) seen in three Canadian emergency departments, between April 2009 and July 2011.
  
  
  METHODS
  Employing a case-crossover design, cannabis and alcohol were identified through blood sample or by self-report. All cyclists involved in a crash and exposure status (cannabis and alcohol) were compared between case period (current crash) and two control periods: prior to the last time the victim cycled around the same time of day; and the typical use prior to bicycling. Crash risk was assessed through conditional fixed effects logistic regression models.
  
  
  RESULTS
  Approximately 15% of cyclists reported using cannabis just prior to the crash, and 14.5% reported using alcohol. Cannabis use identified by blood testing or self-report in the case period and by self-report in the control period yielded a crash risk of 2.38 (1.04-5.43); however, when self-report was used for both the case and control periods the estimate was 0.40 (0.12-1.27). Alcohol use, as measure either in blood or self-report, was associated with an odds ratio of 4.00 (95% CI: 1.64-9.78); results were similar when alcohol was measured by self-report only.
  
  
  CONCLUSIONS
  Cannabis and alcohol use each appear to increase the risk of a non-fatal injury-related crash among bicyclists, and point to the need for improved efforts to deter substance use prior to cycling, with the help of regulation, increased education, and greater public awareness. However, cannabis results should be interpreted with caution, as the observed association with crash risk was contingent on how consumption was measured.
authors.affiliation: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, Nova Scotia B3H 1V7, Canada. Electronic address: Mark.asbridge@dal.ca.
authors.forename: Mark
authors.initials: M
authors.lastname: Asbridge
authors.affiliation: Department of Social and Epidemiological Research, Centre for Addiction and Mental Health, 33 Russell Street, Toronto, Ontario M5S 2S1, Canada; Dalla Lana School of Public Health, University of Toronto, 155 College Street, Toronto, Ontario M5T 3M7, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Mann
authors.affiliation: Injury Prevention Office and Division of Neurosurgery, St. Michaels Hospital, University of Toronto, 30 Bond Street, Toronto, Ontario M5B 1W8, Canada.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Cusimano
authors.affiliation: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, Nova Scotia B3H 1V7, Canada.
authors.forename: John M
authors.initials: JM
authors.lastname: Tallon
authors.affiliation: Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, Nova Scotia B3H 1V7, Canada.
authors.forename: Chris
authors.initials: C
authors.lastname: Pauley
authors.affiliation: Department of Social and Epidemiological Research, Centre for Addiction and Mental Health, 33 Russell Street, Toronto, Ontario M5S 2S1, Canada; Dalla Lana School of Public Health, University of Toronto, 155 College Street, Toronto, Ontario M5T 3M7, Canada; Epidemiologic Research Unit, Clinical Psychology and Psychotherapy, Dresden University of Technology, Mommsenstraße 9, 01069 Dresden, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Rehm
mesh_terms: D000059:Accidents / Q000706:statistics & numerical data*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000428:Alcohol Drinking; D001642:Bicycling / Q000293:injuries; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008385:Marijuana Smoking; D008875:Middle Aged; D018570:Risk Assessment; D055815:Young Adult
keywords: Alcohol; Bicycles; Cannabis; Case-crossover; Crash risk; Injury