The percentage of fatal crashes involving drivers who tested positive for THC in Washington State more than doubled since before marijuana became legalized there, according to a new study by AAA’s Foundation for Traffic Study.
An estimated 21% of all drivers involved in fatal crashes in the state in 2017 tested positive for THC, the psychoactive component in marijuana. The results confirmed an earlier study conducted only two years after the law was enacted.
The actual number of drivers involved in a fatal crash in Washington who tested positive for THC more than tripled from five years before the law took effect to five years after, although this also reflects an increase in the total number of fatal crashes.
The authors emphasized that this study did not examine fault for the crashes, meaning the THC-positive drivers did not necessarily cause the crashes. Having detectable THC in blood does not prove that a person has recently used cannabis and is impaired. THC can stay in the blood for many hours and even days after the impairment wears off, especially in frequent marijuana users. Impairment typically wears off within about 2 to 3.5 hours of smoking, according to the study.
However, other studies have linked cannabis use to an increase in crashes, with one showing that the legalization of recreational marijuana in Washington, Colorado, and Oregon was associated with increased collision claim frequencies compared to states without these laws.