title: Examination of the role of the combination of alcohol and cannabis in South Australian road crashes.
abstract: OBJECTIVE
  The aim of the present study was to examine the role of cannabis in road crashes in South Australia, with a particular focus on the extent to which crashes involving cannabis also involve alcohol.
  
  
  METHODS
  Hospital data, police-reported crash data, and the results of forensic tests of blood samples for drugs and alcohol were collected for 1,074 crash participants (drivers or motorcyclists) admitted to hospital. A sample of 135 coroners' reports was also examined to determine the role of alcohol and cannabis in fatal crashes.
  
  
  RESULTS
  The 3 years of linked data for hospital admission cases revealed that alcohol played a greater role in road crashes than other drugs. Approximately 1 in 5 drivers or motorcyclists had a blood alcohol concentration (BAC) above the legal limit of 0.05. Routine testing for cannabis, methamphetamine, and MDMA revealed a drug-positive rate of approximately 1 in 10 of those tested, with over half of these positive to cannabis. More than a third of cannabis cases also involved alcohol. The majority of those who were positive for alcohol had a BAC above 0.15 g/100 mL. BACs were similarly high among drivers positive for both alcohol and cannabis.
  
  
  CONCLUSIONS
  The findings of the hospital data and the coroners' reports were consistent with each other in terms of providing confirmation that alcohol is still the drug associated with the greatest level of road trauma on South Australian roads. Furthermore, alcohol was also present in around half of the cannabis cases and, when present, tended to be present at very high levels. The results of this study emphasize that, although drug driving is clearly a problem, the most important form of impaired driving that needs to be the target of enforcement is drink driving. Roadside drug testing is important but should not be conducted in such a way that reduces the deterrent value of random breath testing.
authors.affiliation: a Centre for Automotive Safety Research , University of Adelaide , South Australia , Australia.
authors.forename: M R J
authors.initials: MR
authors.lastname: Baldock
authors.forename: V L
authors.initials: VL
authors.lastname: Lindsay
mesh_terms: D000063:Accidents, Traffic / Q000401:mortality / Q000706:statistics & numerical data*; D001334:Automobile Driving / Q000331:legislation & jurisprudence; D002188:Cannabis / Q000009:adverse effects; D003334:Coroners and Medical Examiners; D000431:Ethanol / Q000009:adverse effects / Q000097:blood*; D005260:Female; D006801:Humans; D013287:Illicit Drugs / Q000097:blood; D008297:Male; D008499:Medical Records; D009049:Motorcycles; D016495:Police; D011996:Records; D013021:South Australia / Q000453:epidemiology; D015813:Substance Abuse Detection / Q000706:statistics & numerical data*
chemical_list: D013287:Illicit Drugs; D000431:Ethanol
keywords: alcohol; cannabis; drug driving; fatal crash; hospital data; roadside drug testing