in mass they have "drug recognition experts" they bring in. theres only like 12 in the state. they have to be called in on scene to do their thing for intoxication.
from 2018 (its a thing now, not possibilitry)
Marijuana may now be legal in Massachusetts, but driving under its influence is still strictly prohibited. Some states that years ago legalized the drug for recreational use, such as Colorado […]
www.boston.com
But in the absence of a reliable test for marijuana impairment, Carmichael says the panel should explore the possibility of compelling suspected impaired drivers of submitting to a drug recognition expert, which they can currently refuse.
Massachusetts is
one of just five states that does not have a “implied consent” law for drug-impaired driving. Drivers in the state, by nature of their license, implicitly consent to submit to a breathalyzer if suspected of drunk driving.