ARI SHAPIRO, HOST:
The highest court in the state of Massachusetts is considering roadside sobriety tests, specifically whether the tests that police use to determine drunk driving can also prove a driver is high on marijuana. As NPR's Tovia Smith reports, with more states like Massachusetts legalizing recreational marijuana, this question is becoming more pressing.
TOVIA SMITH, BYLINE: The test has been used for decades to convict drunk drivers.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED POLICE OFFICER: Go ahead and step out here in front of my car, please.
SMITH: Just like in this stop recorded by police in Tennessee, a driver has to stand on one leg, walk a straight line and recite the alphabet.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED MAN: Q - R - S - W - T - S - T - U - V - W - H - Y - Z.
SMITH: The officer can then testify in court how the driver did to make the case for DUI, but defense lawyers argue science has yet to prove that flunking the test really means a person is high. So as attorney Rebecca Jacobstien argued to Massachusetts' high court, the tests shouldn't be allowed in evidence.
(SOUNDBITE OF ARCHIVED RECORDING)
REBECCA JACOBSTIEN: If there's reliable science, reliable science gets to come in, it's just that unreliable science does not.
MICHELLE KING: Your Honor, that is clearly wrong.
SMITH: Attorney Michelle King - for the prosecutors - argued that rapidly advancing science does now prove field tests' reliability.
(SOUNDBITE OF ARCHIVED RECORDING)
KING: Three investigations have come to light, and those are the most important for Your Honors to look at at this point.
SMITH: What makes the stakes so high here is that police do not yet have reliable roadside toxicology tests to say for sure if someone's too high to drive the way a breathalyzer or blood tests can show if someone's too drunk.
MARGARET HANEY: It's complicated. Alcohol is a breeze in comparison.
SMITH: Margaret Haney is a professor of neurobiology at the Columbia University Medical Center. Because marijuana is fat soluble, traces of its main ingredient - THC - can show up in blood, for example, long after a person has sobered up.
HANEY: That just tells you that somebody smoked, but you don't know if they smoked, you know, an hour before or if they smoked a week before or two weeks before.
SMITH: It used to be that police could always fall back on arresting a driver for possession, but with pot now legal, officers worry they'll be faced with more stoned drivers and fewer ways to stop them.
JOHN CARMICHAEL: It couldn't be at a worse time. It's really going to cause a problem out on the street.
SMITH: John Carmichael is police chief in Walpole, Mass.
CARMICHAEL: I mean, police officers know, you know, when there's something off, it's usually quite obvious. So if they take away the ability to do a field sobriety test, I don't know what the police officer on the street is supposed to do.
SMITH: As studies continue on standard field sobriety tests, efforts are also underway to design new ones to better weed out drivers high on weed.
MICHAEL MILBURN: So you can see it's a real app there.
SMITH: University of Massachusetts psychology professor Michael Milburn has invented an iPad test he calls DRUID that specifically measures symptoms of marijuana intoxication like slow reaction time, misperception of time passing and the inability to multitask.
MILBURN: So this says when the circle flashes on the screen, hit the screen where that - where you saw the circle appear. If the square appears, hit the white oval that's going to be on the top of the screen.
SMITH: OK. God help me.
It is not meant to be easy.
MILBURN: Right. 'Cause I figure someone who's stoned is going to go, all right, was it the circle or the square? (Laughter) You know...
SMITH: This is not your grandfather's old count backwards from 10.
MILBURN: (Laughter) Yeah. Well, if you're going to be driving a car, you should be able to perform at a fairly high level.
SMITH: Next, you have to balance on one foot while you hold the iPad in one hand...
Oh, my God.
...Where it records your every wobble.
I'm holding my microphone too, do I get extra points for that?
(LAUGHTER)
SMITH: After four different tests, instead of a police officer's subjective judgment of how you did, the iPad calculates a total score that could be used like the .08 legal limit for alcohol.
So I have...
MILBURN: Your impairment score was 48, which we'd estimate was equivalent to a blood alcohol of .06, so you are not legally drunk.
SMITH: But almost.
MILBURN: Well, you were getting up that there, yeah, yeah, yeah, but a cop would not say I'm taking you in based on what you just did.
SMITH: Milburn says research is just beginning on the reliability of his app. Experts say it won't be long before science validates a whole new generation of impairment tests, but they say they'll only stand up to court challenges when used in conjunction with new and better biological tests that can also prove that the person who was impaired recently used marijuana. Tovia Smith, NPR News, Boston.
(SOUNDBITE OF DAVID BYRNE AND ST. VINCENT SONG, "WHO")