Among fatally injured drivers in Norway, cannabis (THC) impairment was specifically associated with driving without a valid license, while alcohol and stimulant impairment were associated with speeding, no seatbelt, and no license.
Traffic safety researchers, law enforcement, and policymakers working on impaired driving.
THC found in 4% of fatally injured drivers
What the researchers found
THC was found above impairment limits in 4% of fatally injured drivers. Unlike alcohol and stimulants (which were associated with speeding, no seatbelt, and no license), cannabis impairment was specifically associated only with not having a valid driver license. Drug/alcohol-impaired drivers were far more likely to speed (68% vs 32%), skip seatbelts (69% vs 30%), and lack valid licenses (26% vs 1%) compared to sober drivers.
Why it matters
Understanding which risky behaviors accompany which substances can help target enforcement and prevention efforts more effectively.
The numbers in context
772 fatally injured drivers/riders (2005-2015). Alcohol: 20%. Medicinal drugs: 10%. Stimulants: 5%. Cannabis (THC): 4%. Impaired drivers vs sober: speeding 68% vs 32%, no seatbelt 69% vs 30%, no valid license 26% vs 1%.
How the study worked
Retrospective analysis of Norwegian road traffic crash registries and forensic toxicology databases covering fatally injured car/van drivers and motorcycle riders from 2005-2015 (n=772). Multivariable logistic regression adjusted for substance groups, age, and sex.
What this study cannot tell us
Norwegian data may not generalize to other countries. Only fatally injured drivers included, which may not represent all impaired driving. Post-mortem toxicology cannot determine exact impairment at time of crash.
How to read the evidence
Large registry-based study with forensic toxicology confirmation, though limited to fatal crashes in one country.
When this study was published
2019 study using 2005-2015 data from Norway.
The bigger picture
The finding that cannabis-impaired fatal crash drivers had a distinct risk profile (license issues but not speeding) differs from alcohol-impaired drivers, suggesting different intervention approaches may be needed.
Questions still open
- Why is cannabis impairment specifically linked to unlicensed driving? Is this about demographics of cannabis users or a direct behavioral effect?
Common questions
How does cannabis-impaired driving compare to drunk driving in crashes?
How common was cannabis in fatal crashes?
Read the original research
Driver-related risk factors of fatal road traffic crashes associated with alcohol or drug impairment.
Accident; analysis and prevention, 131, 191-199
Citation
Valen, Anja; Bogstrand, Stig Tore; Vindenes, Vigdis; Frost, Joachim; Larsson, Magnus; Holtan, Anders; Gjerde, Hallvard. (2019). Driver-related risk factors of fatal road traffic crashes associated with alcohol or drug impairment.. Accident; analysis and prevention, 131, 191-199. https://doi.org/10.1016/j.aap.2019.06.014