Q: I heard that, in Oregon, you don’t even have to be legally drunk to be arrested for drunken driving? Is this true?

It’s true. In Oregon, it’s not about whether a driver’s blood alcohol level is at or above the state’s legal limit, .08. It’s about the impairment of the driver, said Gretchen McKenzie, the Impaired Driving Program manager for ODOT’s Transportation Safety Division.

Impairment means driving while under the influence of alcohol, drugs, inhalants, or a combination of all three.

But an arrest for DUII is not cut and dried. The law requires a number of steps to determine probable cause for an arrest, Coos Bay Police Officer Steve Myers said.

An officer must first have reasonable suspicion to pull over a driver he believes is impaired, he said.

Reasonable suspicion might include a driver who is driving too fast or too slowly, driving without the car’s headlights turned on, or repeatedly crossing or touching marked roadway lines.

After stopping the driver, the officer is trained to look for other clues, including the smell of alcohol emanating from the person or the vehicle, he said. In addition, a driver who is impaired might experience difficulty finding and presenting his driver’s license, proof of insurance and registration.

If reasonable suspicion still exists, the officer can ask the driver to participate in a field sobriety test, which consists of three parts.

First, the officer will perform the horizontal gaze nystagmus test, or HGN.

The HGN test determines a driver’s level of impairment by watching for changes in the normally smooth movement of the eyes. This is also known as jerk nystagmus.

When a person is under the influence of alcohol, inhalants or other drugs, the substance often interferes with the portion of the brain responsible for the movement of the eyes.

NGN is tested by having a person follow along as an officer moves an object in his field of vision

 Impaired drivers often have trouble following along and overcorrect their eye movements, according to a report from the National Transportation Safety Commission.

Part two of the test is the walk and turn test. The person walks along a fixed line, taking nine heel-to-toe steps before turning and walking back.

The third part of the test is called the one-leg stand, where the officer asks the person to stand on one leg in order to determine his balance.

The driver is scored in each area of the test. The higher the score, the more likely it is that the driver is impaired, according to the Safety Commission.

Not every test has to be performed to determine impairment. For individiuals suspected of being under the influence of drugs, a drug recognition expert is brought in to conduct an additional battery of tests, he said.

The results of the sobriety test, coupled with the initial reasons for the pullover, determine whether an officer has probable cause to arrest the individual, Myers said.

“If a person is impaired to a noticeable and perceptible degree, then they’ll be arrested,” he said.

Only then will the person be taken to jail, where the breath or blood test will determine the level of alcohol in his blood stream. Depending on the number, it can either be used along with other evidence collected to constitute legal impairment in a trial.

The bottom line is that no matter what the reading on the breathalizer, once a driver is taking the test to determine the level of alcohol in his blood, he’s already been arrested, Myers said.

“It’s not about the number,” McKenzie said. “It’s about impairment.”