Every state in the county has a standard for determining whether a motorist is driving under the influence of alcohol, but when it comes to determining if a driver who has smoked marijuana is too high to drive things get a lot more fuzzy.

In an effort to tackle the growing problem of drug-impaired driving, some states that have legalized the use of marijuana have enacted laws that specify the maximum amount of THC that a driver can have in their system based on a blood test. But that's not a reliable way to test a driver for marijuana impairment, and may result in some motorists being wrongfully convicted while dangerous drivers go free. That's the conclusion of new research out Tuesday from the AAA Foundation for Traffic Safety.

THC is the main chemical component in marijuana that can impair driver performance and affect the mind.

But unlike alcohol, which studies has shown to increase crash risk as the blood alcohol concentration rises, research shows that drivers who use pot don't become impaired at a specific level, meaning a driver with a low level of THC in their system might be unsafe behind the wheel while another with higher levels of THC may not be impaired. That makes it hard to develop laws that are fair and consistent, the AAA Foundation study said.

Yet, there is concern about drug-impaired driving after research in Washington state found that one in six drivers involved in fatal crashes in 2014 had recently used pot.

“The significant increase in fatal crashes involving marijuana is alarming,” said Peter Kissinger, President and CEO of the AAA Foundation for Traffic Safety. “Washington serves as an eye-opening case study for what other states may experience with road safety after legalizing the drug.”

Alaska, Colorado, Oregon and Washington, along with Washington D.C., have legalized recreational use of the drug and another 24 states, including Minnesota, have legalized it for therapeutic and medicinal use.

A handful of states such as Montana, Washington, Nevada, Ohio, Colorado and Pennsylvania have what are called "per se" laws, or the legal limits of THC that can be in a driver's system. The laws are similar to the .08 BAC laws with motorists who test about those limits subject for conviction. Twelve states forbid the presence of any levels of the drug.

“There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment, in the same manner as we do with alcohol,” said Marshall Doney, AAA’s President and CEO. “It’s simply not possible today to determine whether a driver is impaired based solely on the amount of the drug in their body.”

Instead of relying on an arbitrary number, the foundation's report said police should be trained to more effectively identify behavioral and physiological evidence of driver impairment.

In the past five years in Minnesota, the number motor vehicle deaths in which marijuana was detected has rised from 14 in 2011 (11 drivers, 3 passengers) to  32 last year (25 drivers, 2 passengers, 1 pedestrian, 2 bicyclists, 1 personal conveyance (wheelchair), 1 unknown),  according to the Department of Public Safety.

Whether the use of marijuana is legal or not, all motorists should avoid driving while impaired, the study said. Just because a drug is legal does not mean it is safe to use while operating a motor vehicle. Drivers who get behind the wheel while impaired put themselves and others on the road at risk, the study said. .

“Marijuana can affect driver safety by impairing vehicle control and judgment,” continued Doney. “States need consistent, strong and fair enforcement measures to ensure that the increased use of marijuana does not impact road safety.”

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