Police are already preparing for more traffic stops in anticipation of the legalization of the recreational use of marijuana in Connecticut – but testing drivers for marijuana use is much harder than one may think.

News 12’s John Craven spoke with Norwalk Police Officer Tyrone Boyd, a federally-certified Drug Recognition Expert. After a suspect fails a field sobriety test, Boyd uses various medical tools to determine whether a driver is high and which drug they may have taken. He says certain drugs affect a person’s pupil size. Boyd also measures the suspect’s pulse, as well testing their awareness of time, which can be significantly affected by marijuana use. 

The test is 12 steps and takes up to an hour.

Currently, there are only 56 DREs in Connecticut. But once recreational marijuana is legal, residents can expect many more of them.

The Connecticut ACLU says there's no scientific basis for drug recognition tests.

"Police are police. They're not nurses. They're not doctors,” says Dan Barrett, the group’s legal director. “I'd pay attention to whether they have the knowledge to give these tests and interpret them correctly."

In Georgia, the group is suing over mistaken arrests. At least four states don’t accept drug recognition officers as expert witnesses. About a dozen others do.

In Connecticut, a DRE test is voluntary, but under the new marijuana law, drivers would have to submit to one or immediately lose their license.

Boyd had to complete a month of rigorous DRE training, including real-world tests in Arizona.

He stands by the test.

"It was probably the most stressful training I've ever had in my life,” he said. "You have to successfully complete 12 drug evaluations, and we actually did those on actual inmates."

Norwalk has two of drug recognition experts. If a neighboring department needs one, they can also lend them out.

If the marijuana bill passes, drivers who fail a field sobriety test would have to agree to a drug recognition test. That rule would start next April.