Summary of peer-reviewed studies and authoritative reports
Key Takeaways for Legislators
- Cannabis alone does not significantly increase risk of motor vehicle collisions.
- Alcohol remains the dominant factor in increased crash risk.
- Evidence from Canada and US states shows legalization and decriminalization do not drive population-level crash increases.
- Policy implication: Blanket bans on cannabis to prevent crashes are not supported by current data; focus should remain on preventing alcohol-impaired driving.
| Study / Link | Scope / Findings | Key Conclusion |
| Risk of motor vehicle collision associated with cannabis and alcohol use among patients presenting for emergency care | Emergency department patients; analyzed cannabis alone, alcohol alone, and combined use | Cannabis alone is not associated with higher odds of crashes. Alcohol alone and alcohol + cannabis increased risk. High self-reported cannabis use is linked to lower odds of collision. |
| Assessing the Impact of Marijuana Decriminalization on Vehicle Accident Experience (Canada / US) | Analysis of insurance claims pre- and post-decriminalization | No statistically significant change in crash frequency or cost after legalization. |
| Canada’s cannabis legalization and drivers’ traffic-injury presentations (Ontario & Alberta, 2015-2019) | ED visits for traffic injuries pre/post Cannabis Act | No significant post-legalization changes in traffic-injury presentations for all drivers or youth drivers. |
| Marijuana laws and pedestrian fatalities in the United States | US states with liberalized marijuana laws; pedestrian fatalities | Liberalization associated with lower pedestrian fatalities, likely due to alcohol substitution. No evidence that cannabis increases fatalities. |
| Did the cannabis recreational use law affect traffic crash outcomes in Toronto? | Toronto; Cannabis Act and number of cannabis stores | No significant change in traffic crashes; slight non-significant decrease in incidence rates. |
| Study: No Correlation Between THC Detection and Driving Impairment | Experienced cannabis users; measured THC levels vs driving performance | No correlation between THC levels in blood, breath, or oral fluid and driving performance. Per se laws for THC not supported by evidence. |
| UI study: Car insurance premiums fall in states where medical marijuana is legal | Insurance premium data across US states | States with medical cannabis did not see higher risk, premiums fell, suggesting no increase in accidents. |
| Traffic fatalities within US states that legalized recreational cannabis sales and their neighbors | Colorado, Washington, Oregon and neighboring states; fatality trends | Temporary increase of ~1 fatality per million residents after legalization, but trend reductions followed; effect minimal compared to population size. |
| US Department of Transportation: Drug and Alcohol Crash Risk Study | Nationwide crash risk study controlling for age, gender, alcohol | THC use is not associated with increased crash risk when controlling for demographics and alcohol use. |
| Recreational cannabis legalization on rates of traffic injury in Canada | Canada; traffic injury rates pre/post legalization | No notable impact on motor vehicle, pedestrian, or cyclist injuries. |
| Canada’s cannabis legalization and drivers’ traffic-injury presentations | ED visits analysis | No evidence of significant post-legalization changes in traffic-injury presentations. |
