Six states currently have legal limits on THC blood content for drivers, and as many as eleven more may be voting to impose them in November’s elections. But a new report from AAA, the country’s largest automobile club, says that while there is a need for regulation of drivers’ weed inebriation, none of the regulatory systems in place do so with scientific accuracy.

“Legal limits, also known as per se limits, for marijuana and driving are arbitrary and unsupported by science,” the report says, while also citing the rise in cannabis-related automobile fatalities.

“Fatal crashes involving drivers who recently used marijuana doubled in Washington after the state legalized the drug… and these findings serve as an eye-opening case study for what other states may experience with road safety after legalizing the drug.”

The report advocates doing away with laws that determine a driver’s sobriety by measuring the THC in their blood and replacing them with new laws that determine driver impairment through more accurate criteria.

The problem with testing THC in a driver’s system is that the chemical behaves very differently than alcohol. While alcohol runs through the body pretty quickly, making a driver’s blood alcohol content a fairly reliable way to gauge their impairment, THC metabolites can hang around in the body for weeks after consumption, especially in the bodies of regular consumers.

Paradoxically, THC can also diminish rapidly in the body, particularly in people who don’t use cannabis very often. That means that regular cannabis users may be likely to test over the limit for THC, even when they’re not stoned, while non-frequent cannabis users can test under the limit while they’re impaired. In short, using THC content to judge impairment is bunk.

AAA suggests an alternate method to enforcing sobriety for drivers. Field sobriety tests from trained officers and backed up by additional blood testing would be a far more accurate tactic, the group says. There are dozens of physical manifestations of drug use which can be screened for, including tongue color and pupil dilation.

“There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol,” said AAA president and CEO Marshall Doney in an Associated Press article. “In the case of marijuana, this approach is flawed and not supported by scientific research.”


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