title: The prevalence of cannabis-involved driving in California.
abstract: BACKGROUND
  Various national surveys suggest that cannabis use is rising nationally and many States have passed legislation that has potential to increase usage even further. This presents a problem for public roadways, as research suggests that cannabis impairs driving ability.
  
  
  METHODS
  Anonymous oral fluid samples and breath tests were obtained from more than 900 weekend nighttime drivers randomly sampled from six jurisdictions in California. Oral fluid samples were assayed for the presence of Schedule I drugs. Drivers also completed information on self-reported drug use and possession of a medical cannabis permit. Data from the 2007 National Roadside Survey (collected using comparable methods) were used as a comparison.
  
  
  RESULTS
  Using the 2010 data, a total of 14.4% of weekend nighttime drivers tested positive for illegal drugs, with 8.5% testing positive for delta-9-tetrahydrocannabinol (THC). THC-positive rates varied considerably among jurisdictions, from a low of 4.3% in Fresno to a high of 18.3% in Eureka. A comparison with the 2007 NRS data found an increase in THC-positive drivers in 2010, but no increase in illegal drugs other than cannabis. Drivers who reported having a medical cannabis permit were significantly more likely to test positive for THC.
  
  
  CONCLUSIONS
  Cannabis-involved driving has increased in California since 2007. Nearly 1-in-10 weekend, nighttime drivers tested positive for THC, and in some jurisdictions, the rate was nearly 1-in-5. The possible contribution of cannabis legislation, such as decriminalization and medical cannabis usage, is discussed.
authors.affiliation: Pacific Institute for Research and Evaluation, Calverton, MD 20770, USA. mjohnson@pire.org
authors.forename: Mark B
authors.initials: MB
authors.lastname: Johnson
authors.forename: Tara
authors.initials: T
authors.lastname: Kelley-Baker
authors.forename: Robert B
authors.initials: RB
authors.lastname: Voas
authors.forename: John H
authors.initials: JH
authors.lastname: Lacey
mesh_terms: D000293:Adolescent; D000328:Adult; D000428:Alcohol Drinking / Q000453:epidemiology; D001334:Automobile Driving / Q000706:statistics & numerical data*; D002140:California / Q000453:epidemiology; D002186:Cannabinoids; D003625:Data Collection; D013759:Dronabinol / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay; D005006:Ethnicity; D006801:Humans; D013287:Illicit Drugs; D007880:Legislation, Drug; D008385:Marijuana Smoking / Q000453:epidemiology*; D012306:Risk; D012959:Socioeconomic Factors; D055815:Young Adult
chemical_list: D002186:Cannabinoids; D013287:Illicit Drugs; D013759:Dronabinol
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