A public hearing is underway in Augusta on a proposal to set a blood-level limit to determine when someone is driving under the influence of marijuana.

The bill being considered by the Legislature’s Criminal Justice and Public Safety Committee would set the level for operating under the influence at 5 nanograms of THC per 100 milliliters of blood. The level would be zero nanograms for drivers under 21. If approved, Maine would join a half-dozen states with similar restrictions.

How to deal with impaired drivers was anticipated to become a more pressing issue as Maine considered joining four other states and the District of Columbia in legalizing marijuana for recreational marijuana, but that issue will not be put to voters this year. The secretary of state announced Wednesday that a citizens’ initiative to legalize recreational marijuana did not qualify for the ballot after it fell short of the required number of signatures by about 10,000.

The marijuana OUI bill, LD 1628, stems from recommendations made in December by a working group charged with looking at the issue. The group was convened by the secretary of state in response to an earlier bill that would make it a crime to drive a car while having a THC level of 5 nanograms or more per milliliter of blood.

Members of the study group recommended that the state pass a law setting a blood-level limit that determines when someone is driving under the influence, but were split on what level of THC in the blood would show impairment. Some members pointed out that the scientific community is divided on the issue and said uncertainty could lead to false convictions.

So far, six other states have set legal limits for the concentration of tetrahydrocannabinol – or THC, the psychoactive ingredient in marijuana – in the blood. Colorado, Washington and Montana have set an intoxication level of 5 nanograms or more of THC per milliliter of blood.

Maine’s law against operating under the influence already prohibits driving a motor vehicle while impaired by marijuana, but there is no specific breath or blood-level limit like there is with alcohol.

Recent research into the effect of marijuana use on drivers is mixed, although many studies indicate drivers are less impaired by marijuana than by alcohol and tend to make fewer risky choices than drunken drivers. The National Institute on Drug Abuse maintains that marijuana significantly impairs judgment, motor coordination and reaction time, but other research shows drivers impaired by marijuana overcompensate by driving more slowly and avoiding passing other cars.

There is no simple roadside test for marijuana similar to the breath test used to determine blood-alcohol content. Police officers currently use a drug recognition exam on the roadside to detect impairment from drugs. But some say officers need better tools to stop drugged driving as the culture becomes more accepting of marijuana use.

This story will be updated.

Gillian Graham can be contacted at 791-6315 or at:

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Twitter: @grahamgillian