title: The impact of marijuana decriminalization on California drivers.
abstract: BACKGROUND
  The liberalization of marijuana laws has led to concerns that such changes will increase "drugged driving" and crash-related mortality. California decriminalized marijuana effective January 1, 2011; we examine the impact of this change on marijuana-involved driving.
  
  
  METHODS
  We used laboratory testing from roadside surveys and the Fatality Analysis Reporting System (FARS) to assess impacts on weekend nighttime drivers and fatally injured drivers, respectively. We calculated marijuana prevalence (measured by laboratory-confirmed delta-9-tetrahydrocannabinol [THC] in roadside surveys and cannabinoids in FARS) and compared corresponding 95% confidence intervals (CI) to identify statistically significant changes post-decriminalization. We also conducted multiple logistic regression analyses to determine whether the odds of marijuana-involved driving increased significantly after controlling for potential confounders.
  
  
  RESULTS
  There was no statistically significant change in the prevalence of THC-positive driving among weekend nighttime drivers (n=894) in 2012 (9.2%; 95% CI: 6.3, 12.2) compared to 2010 (11.3%; 95% CI: 8.5, 14.0) or in the adjusted odds of testing positive for THC (adjusted odds ratio [AOR]=0.96; 95% CI: 0.57, 1.60). In contrast, we found a statistically significant increase in the prevalence of cannabinoids among fatally injured drivers in 2012 (17.8%; 95% CI: 14.6, 20.9) compared to the pre-decriminalization period 2008-2010 (11.8%; 95% CI: 10.3, 13.3). The adjusted odds of testing positive for cannabinoids were also significantly higher in 2012 (AOR=1.67; 95% CI: 1.28, 2.18).
  
  
  CONCLUSIONS
  Our study generated discrepant findings regarding the impact of decriminalization on marijuana-involved driving in California. Factors that may have contributed to these findings, particularly methodological factors, are discussed.
authors.affiliation: Pacific Institute for Research and Evaluation, 11720 Beltsville Drive, Suite 900, Beltsville, MD 20705, United States. Electronic address: rpollini@pire.org.
authors.forename: Robin A
authors.initials: RA
authors.lastname: Pollini
authors.affiliation: Pacific Institute for Research and Evaluation, 11720 Beltsville Drive, Suite 900, Beltsville, MD 20705, United States. Electronic address: romano@pire.org.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Romano
authors.affiliation: Pacific Institute for Research and Evaluation, 11720 Beltsville Drive, Suite 900, Beltsville, MD 20705, United States. Electronic address: mjohnson@pire.org.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Johnson
authors.affiliation: Pacific Institute for Research and Evaluation, 11720 Beltsville Drive, Suite 900, Beltsville, MD 20705, United States. Electronic address: lacey@pire.org.
authors.forename: John H
authors.initials: JH
authors.lastname: Lacey
mesh_terms: D000063:Accidents, Traffic / Q000706:statistics & numerical data*; D001334:Automobile Driving / Q000706:statistics & numerical data*; D002140:California; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000331:legislation & jurisprudence*
keywords: California; Cannabis; Driving; Marijuana; THC