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Drug and Driving: A Compendium of Research Studies
Annotated Sources
International
1. Bates, M.N. and Blakely, T.A. (1999). Role of cannabis in motor vehicle crashes. Epidemiology Review 21: 222-232.
Overview
Review article of the role of cannabis in motor vehicle collisions
Type of study, population(s) and proportion tested
Review of 5 existing studies examining the risks associated with cannabis in motor vehicle collisions
Re-analysis of data was presented for most studies reviewed
Culpability analysis
Drugs examined
Method of testing and medium used
Various methods were used in different studies
Other dependent variables
Findings (including statistical methods)
3 studies show reduced risk of culpability for fatal crash involvement -- weighted OR of .59, p=.05
2 injury studies -- one shows increased risk, one shows decreased risk
Risk of alcohol/cannabis combination higher than alcohol alone but not significantly so (small number of cases)
Comments
Author identifies several limitations of culpability studies
Drivers who have used cannabis modify their driving behaviour to compensate for perceived impairment by driving slower, taking fewer risks, and leaving more headway
Not possible to exclude possibility that cannabis alone or in combination leads to increased risk of crash in less serious crashes
2. Gemmell, C.; Moran, R.; Crowley, J.; and Courtney, R. (1999). Literature Review on the Relation between Drug Use, Impaired Driving and Traffic Accidents. CT.97.EP.14. Lisbon, Portugal: European Monitoring Centre for Drugs and Drug Addiction.
Overview
This report summarizes the general findings of drugged driving, with respect to a variety of drugs, and discusses some of the problems associated with epidemiological and experimental studies in this area
Type of study, population(s) and proportion tested
Literature review
Drugs examined (threshold values for detection)
Findings (including statistical methods)
- Epidemiological studies:
- Unclear whether accidents occur as a direct result of the drug in question
Often no comparison group
Drugs often mixed with alcohol
Presence of drugs does not necessarily imply impairment - Simulation techniques:
- Introduces artificiality and ethical issues, with respect to giving high doses of drugs to subjects
- Alcohol:
- No drug found as frequently as alcohol
- Methadone:
- Not found often and studies do not suggest sufficient impairment
- Cannabis:
- One of the most prevalent drugs, though often found mixed with alcohol, which is more likely to result in an increased risk of accident
- Benzodiazepines:
- Most frequently detected licit drug which can double the risk of accident, especially in older (over 65) drivers and when mixed with alcohol
- Antihistamines:
- Seldom suggested as causal in accidents
- Antidepressants:
- Effects of severe depression may have greater impact on Driving
- Amphetamines:
- Insufficient evidence, largely due to lack of controlled studies, but, in high does, it is likely to increase driving impairment
- Ecstasy and other synthetic drugs:
- More research is required, but they are likely to be a danger to driving
3. Kelly, E., Darke, S. and Ross, J. (2004). A review of drug use and driving: Epidemiology, impairment, risk factors and risk perceptions. Drug and Alcohol Review 23: 319-344.
Overview
Review of drug use and driving literature
Type of study, population(s) and proportion tested
Review
Drugs examined (threshold values for detection)
Method of testing and medium used
Other dependent variables
Findings (including statistical methods)
Drug driving prevalence approximately 4% in past 12 months
Up to 25% of crash-involved drivers positive for drugs
Cannabis is the most common, followed by benzodiazepines, cocaine, amphetamines, opioids -- polydrug use common, as is overlap with alcohol
Cannabis and benzodiazepines increase risk
Unclear as to whether there exists an association between drug use problems and drug driving
Less concern about impaired driving among drug drivers and drink drivers -- perception is that drugs do not significantly impair driving performance
Risk perceptions vary according to drug type -- cannabis seen as producing less impairment than others, including alcohol
Research and interventions should focus on high-risk groups.
4. Ramaekers, J. G., Berghaus, G., van Laar M., and Drummer, O. H. (2004). Dose Related risk of motor vehicle crashes after cannabis use. Drug and Alcohol Dependence 73: 109-119.
Overview
Studies of cannabis prevalence and relative risk to driving are reviewed. Both epidemiological and experimental studies are discussed.
Type of study, population(s) and proportion tested
Literature review
Drugs examined (threshold values for detection)
Findings (including statistical methods)
- Epidemiological studies:
- Prevalence of THC between 4 and 14% in injured or fatally injured drivers
- In the absence of control groups, role of THC in collisions cannot be determined
- Culpability studies:
- Cannabis in combination with alcohol have shown significant increases in culpability rates
- Looking specifically at THC presence, crash culpability increases with increases doses of THC (OR of 2.7 compared to drug-free drivers)
Case-control studies:
OR for accident or injury, for those with THC present or having used cannabis within so many hours of driving, ranged from 2.3-2.9
When in combination with alcohol, OR ranged from 4.6-80.5
- Experimental studies:
- In interactive simulators (dose up to 200 kg), THC has been found to increase lateral position variability, headway variability, and speed variability and cause subjects to ignore navigational information, hit roadway obstacles, and react more slowly to secondary demands
- In actual driving situations, (THC dose of 8.4 mg) concentration, care while driving, and judgement were significantly affected
- When cannabis combined with alcohol, more severe performance impairments were found
5. Thomas, R.E. (1998). Benzodiazepam use and motor vehicle accidents -- systematic review of reported association. Canadian Family Physician 44: 799-808.
Overview
Review of relationship between benzodiazepine use and motor vehicle collisions
Type of study, population(s) and proportion tested
Review of case-control, police or emergency studies and experimental driving studies of the effects of benzodiazepines
Drugs examined (threshold values for detection)
Benzodiazepines
Method of testing and medium used
Other dependent variables
Examines impaired driving, crashes, mortality, medical cases, hospitalization
Findings (including statistical methods)
OR for mortality and emergency medical treatment range 1.45 to 2.4
In police and emergency ward studies, benzodiazepines a factor in 1% to 56% of crashes (usually 5 to 10%)
In cases where BAC was below legal limit, benzodiazepines were found in 43 to 65% of cases
In controlled one controlled study, 5% of drivers and 2% of controls in crashes had benzodiazepines present
Benzodiazepines double risk of motor vehicle collision
For driver >65 years of age, risk is higher when taking longer acting and larger quantities of benzodiazepine
6. Ward, N.J. and Dye, L. (1999). Cannabis and Driving: A Literature Review and Commentary. Road Safety Research Report, No. 12. London: Department for Transport, Local Government and the Regions.
Overview
Literature review on cannabis and driving
Type of study, population(s) and proportion tested
Literature review and commentary
Drugs examined (threshold values for detection)
Cannabis
Method of testing and medium used
Other dependent variables
Findings (including statistical methods)
Cannabis was considered to cause clear impairment on laboratory tasks such as tacking and attention
Impairment was not as pronounced on real driving or simulator tasks
Compensatory effort could be invoked to offset the impairing effects 4-12% of fatalities test positive for cannabis -- most cases confounded by alcohol
Baseline data for non-crash cases absent
Authors suggest that the equivalent of legal alcohol limit (80 mg/100 ml) for cannabis is 11 ng/ml THC
Study notes that the research has been piecemeal with numerous problems and gaps. No firm conclusions could be drawn.
