Measuring marijuana’s influence on driving ability proves difficult
The scientific community has yet to form a consensus on how to accurately measure marijuana’s impact on a motorist’s driving ability, according to The Boston Globe, a problem that is drawing more attention in the wake of a car crash that killed a law enforcement officer.
Dr. Kevin Hill, assistant professor of psychiatry at McLean Hospital, told the Globe that scientists agree that marijuana and alcohol can compromise a motorist’s driving ability. But the substances also affect the brain’s functions differently.
From the Globe:
“With too much alcohol, drivers are likely to make ’errors of omission,’ such as not checking their rearview mirror, while marijuana users tend toward ‘errors of commission,’ such as driving too slowly, Hill said.’’
While law enforcement officials can measure a motorist’s alcohol consumption with a breath test, a reliable standard test for measuring tetrahydrocannabinol, the main chemical in marijuana, also known as THC, does not exist.
There is also little agreement within the scientific community about how much THC in a person’s system results in impairment. This is because marijuana can affect individuals differently, depending on their consumption habits.
Earlier this month, the AAA Foundation for Traffic Safety found fatal crashes involving marijuana more than doubled in Washington state after marijuana was legalized for recreational purposes in 2012.
However, AAA also notes that setting legal limits for marijuana can be “problematic’’ because there is no scientific evidence that drivers become impaired once a certain level of marijuana is consumed.
Testing for THC in a suspect’s blood is also difficult because levels can drop during the time it takes to obtain a sample and perform a test. The questions arise as a motorist faces charges for driving under the influence of marijuana he bought legally at a medical dispensary, resulting in a fatal car crash that claimed the life of a Massachusetts state trooper.
Massachusetts voters could have to decide this November whether to legalize recreational marijuana for people over 21 years old.
Read the Globe story here.
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