Recent court cases involving deaths allegedly caused by people driving under the influence of marijuana have led to a heightened awareness about the issue, which some sources have linked to the increasing acceptance of medical marijuana.

In one of the cases, a California driver pleaded guilty to manslaughter, while another driver there was found not guilty of that charge because the effects of the drug found in his system couldn’t be proved in court.

In alcohol-related offenses, a legal blood-alcohol standard says that any adult with more than 0.08 percent is legally drunk (lower standards apply to minors in some states). To determine that, officers can apply tests to drivers stopped on suspicion of OUI. Come up with an 0.08 level or higher and you’re busted, period.

But what happens when a driver has been smoking marijuana? Blood tests can detect the weed’s presence, but there are no legal standards for how much is too much. That means it is often more difficult to make an arrest stick in court.

And some law enforcement agencies assert that the availability of marijuana for medicinal purposes — and the inconsistent application of federal laws that still make its possession and sale illegal in most circumstances — mean that police and prosecutors are confronting more people who could well be one toke (or more) over the line while on the public highways.

Medical marijuana is legal in about a third of U.S. states, including Maine.

But lacking either a legal standard for consumption or a standardized test for the effect of the substance in a person’s system, police have to fall back “impairment,” a standard that some prosecutors say is harder to establish in court.

Thirteen states have resolved the issue by adopting a zero-tolerance standard — if tests show pot use, that’s a legal violation.

The rest, including Maine, make police judge impairment levels. Police have a number of tests for that, including stability, pupil size and the ability to estimate the passage of time.

Advocates of medicinal use say the zero-tolerance standard means people who use pot as medicine are being penalized by being forbidden to drive.

That could be resolved by research now under way to find an easy test for marijuana levels in the body and for the amounts that would mean a person is unsafe to drive. But experts say reliable tests are still years away, and so law enforcement is still on its own.

And so are sober drivers, who deserve protection against all impaired motorists — no matter how they got that way.

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