HARTFORD, Conn. (WTNH) — If a driver is operating a vehicle while under the influence of alcohol, the traffic stop is relatively straightforward.

But if an officer administers a breathalyzer test to someone who has used cannabis, the driver will blow a zero. Instead, police must lean on science to determine if someone is under the influence.

After someone has been arrested, police call in a drug recognition expert, who then uses a 12-step process to determine what drug someone may be under the influence of, according to Sgt. Christine Jeltema with the Connecticut State Police.

Officers may also rely on A-RIDE, which stands for Advanced Roadside Impaired Driving Enforcement, as a field sobriety test for cannabis.

In Connecticut, drivers have up to five ounces of marijuana in their vehicles. However, that has to stay in the glove box or the trunk.

As recreational marijuana sales become legal in the state on Tuesday, driving while under the influence is something law enforcement officers will be on the lookout for.

Doctors at the Yale School of Medicine suggest small, slow doses when using recreational marijuana.

Unlike alcohol, THC can be smoked, eaten, or absorbed through the skin. Each of those methods changes the intensity and length of a high.

“So someone who is used to thinking about marijuana as having effects that last maybe 45 minutes or an hour by smoking, and they think the same applies to consuming an edible,” Dr. Deepak Cyril D’Souza said. “It’s very different because the body absorbs and metabolizes it differently, so the effects last much longer.”

He said there hasn’t been much research about what happens if a driver smokes marijuana and then gets behind the wheel.

“Someone may have one drink and think one drink is fine, and then smoke a little weed, which in itself may be fine, but the combination of the two may have additive effects or synergistic effect on driving,” D’Souza said.

Whether under the influence of alcohol or marijuana, the penalties — and dangers — of DUI are the same.