Does Driving under the Influence of Cannabis Lead to Traffic Offenses?
A 2022 report by the National Transportation Safety Board (NTSB)[1] examined data from Orange County, CA:
"The Orange County laboratory provided 2 years of data between August 1, 2018, and July 30, 2020, on 14,051 drivers arrested for impaired driving offenses."
From the study:
Finding 1
4,613 (32.8%) tested positive for THC
10,827 (77.1%) tested positive for Alcohol
Finding 2
Only 1.1% did not test positive for any substance
51.3% tested positive for only 1 substance
47.6% tested positive for 2 or more substances
Finding 3
685 (4.9%) tested positive for cannabis only
Additional Point 1
There is no correlation between testing positive for THC and being impaired, since:
THC affects each person differently, depending on tolerance
Cannabis remains in the body for up to several weeks after use.[2]
Additional Point 2
According Monitoring the Future[3], roughly 20% of the adult population reports using cannabis monthly. Given the tendence to under-report use, the prevalence of use may be much higher. This begs the question: What portion of drivers not involved in traffic incidents would test positive for THC?
Conclusions
Taken together, the information suggests that substance use and driving is complicated. Indeed, the NTSB concluded:
As a result of this research, the NTSB identified the following safety issues: (1) the need to implement proven countermeasures for alcohol-impaired driving; (2) the need to address the growing problems of cannabis-, other drug-, and multiple-drug-impaired driving; (3) the need to improve drug-impaired driving laws and enforcement; (4) the need to ensure that driving safety is considered in the evaluation of prescription and OTC drugs; and (5) the need to enhance systems for documenting and tracking the incidence of drug use and driving.
At the same time, I’d say that the hype about cannabis use causing traffic accidents is a bit overblown, especially when the full context is taken into account.
Furthermore, as cannabis continues to displace alcohol and other drugs/medications,[4] traffic accidents should drop.
[1] Alcohol, Other Drug, and Multiple Drug Use Among Drivers. NTSB. 2022 Dec 13. https://www.ntsb.gov/safety/safety-studies/Documents/SRR2202.pdf
[2] Theisen E. How Long Does Weed Stay in Your System? Healthline. 2024 Apr 23. https://www.healthline.com/health/how-long-does-weed-stay-in-your-system
[3] Cannabis: Trends in 30 Day Prevalence among Respondents Aged 19 through 65. Monitoring the Future. https://monitoringthefuture.org/data/panel/substance-use/#drug=%22Cannabis%22
[4] Lucas P et al. Medical cannabis patterns of use and substitution for opioids & other pharmaceutical drugs, alcohol, tobacco, and illicit substances; results from a cross-sectional survey of authorized patients. Harm Reduct J. 2019. https://harmreductionjournal.biomedcentral.com/articles/10.1186/s12954-019-0278-6