Legalizing marijuana would not change how DUI laws are enforced here, according to a state police expert.
That's because of a 1-year-old state law that was designed to crack down on people who drive while impaired by prescription drugs and other legal medications.
RSA 265-A:2 makes it illegal to drive - or operate a boat - while "under the influence of intoxicating liquor or any controlled drug, prescription drug, over-the-counter drug, or any other chemical substance, natural or synthetic, which impairs a person's ability to drive."
That law was amended in 2012 to include the broader range of substances and took effect Jan. 1, 2013.
"New Hampshire wisely chose to say you cannot drive a car impaired by any chemical substance, regardless of ... whether or not a drug is controlled," said Lt. Matthew Shapiro, commander of special services/highway safety for New Hampshire State Police.
The law sets a legal limit of .08 blood-alcohol content for adults and .02 for those under 21. But there is no "per se" limit for legal or illegal drugs, according to Shapiro,
"Alcohol is the only chemical compound that has a per se limit because it has a linear and very well-studied progression of impairment," he explained.
For any other substance, police rely on other evidence, such as driving behavior, field sobriety tests and the arresting officer's observations.
If a police officer stops a driver for erratic driving and smells pot, for instance, the officer would look for signs and symptoms of impairment, such as slurred speech, confusion, slowed thought process or staggering gait, Shapiro said.
If the driver is arrested for DUI, police will call in a drug recognition expert (DRE) trained to recognize signs and symptoms of impairment from different drugs, said Shapiro, who is a DRE. That expert will then form an opinion about whether the person is impaired "and what they're likely impaired by."
"Then the person would very likely be asked to submit to a blood test at that point, which is a confirmatory test."
Even if the individual refuses to submit to such a test, Shapiro said, police can still charge him with DUI based on the "totality of evidence."
Asked what would change if New Hampshire legalized marijuana, Shapiro said, "Nothing." That's because of the change in the DUI law to include any chemical substances, even legal ones.
There are plenty of legitimate arguments against legalization, he said. But he said fears that police would not be able to arrest impaired drivers shouldn't be one of them.
"There is no out on DUI," Shapiro said. "We take that very seriously."