The police pull you over. When the officer comes up to the car, he tells you that he thought you ran a stop sign. You don’t even feel sure that you did, but you hand over your license and registration. The officer goes back to his car for a minute and then comes back up.

That’s when things get interesting. The officer asks you if you will get out of the car. You quickly tell him that you have not had anything to drink, but you get out anyway. The officer asks you to do some field sobriety tests. They’re the old standards — walking in a straight line, standing on one leg, and all the rest. You fail one of them because you trip while walking in a straight line.

You weren’t drunk

The officer then gives you a breath test, which shows that you told the truth. You didn’t drink before getting in the car. For a moment, you think you’re going home.

But the officer nods like he suspected this all along. He says that he thinks you are high on marijuana. He arrests you for driving under the influence. He says the reason for the arrest is the failed field test.

Does a field sobriety test provide adequate evidence?

Forget, for a moment, whether you smoked marijuana or not. Your real question here is whether the officer can use the field sobriety test as evidence. The breath test cleared you of alcohol use, after all, and it does not pick up marijuana. Are those field tests enough?

They’re not. In a ruling in 2017, the highest court in Massachusetts said that officers cannot use those tests and their observations as evidence when they get to court.

A scientific issue

The problem with the tests is scientific. They were designed to catch drunk drivers. Studies and research back up the fact that they work for that purpose.

Those same studies say nothing about marijuana use. So, using them to detect marijuana has no scientific basis at all. While the tests may seem sufficient to officers on the ground, the reality is that they were never designed for marijuana, and they were never studied to see if they can detect marijuana use.

On top of that, the court cast doubt on whether officers could even tell, based on the tests, that someone was high. It pointed out that marijuana impacts people far differently than alcohol. An untrained observer, like a traffic officer, may have no idea if a driver is high or not.

Your rights

If you are arrested for a marijuana-related driving offense, it pays (for you and especially your attorney) to know the history of relevant court cases. Be sure you also understand your legal rights.