It’s 1:30 Saturday morning.

You’re on your way home from a night out with friends.

You make a left turn onto Highway 20, your mind still buzzing from the night’s events.

Suddenly, flashes of red and blue light up your rearview mirror.

You pull to the shoulder and fish around for your license, registration and proof of insurance, all the while wondering what on earth you’re being stopped for.

Remember that left turn you made? You forgot to use your turn signal.

It’s an innocuous goof to you, but not to the Washington State Patrol trooper who just happened to be following you.

Not using a turn signal is just one of the many subtle clues troopers look for when they’re seeking out potentially impaired drivers.

Most of the time, the drivers in question are just forgetful or distracted.

But not always.

Last year, troopers arrested 256 impaired drivers on Whidbey Island, and one DUI crash resulted in a fatality. This year, there have been 237 DUI arrests so far, and a staggering five fatalities from DUI crashes.

“We’re here to protect people because sometimes they’re not there to protect themselves,” Trooper Norman Larsen said.

Last Friday night, law enforcement officers, including State Patrol troopers, participated in the “Night of 1,000 stars,” which emphasized getting drivers under the influence of alcohol or drugs off the road.

But finding those impaired drivers is not an exact science.

Most impaired drivers are spotted due to their inattentive driving. Larsen said when a person is under the influence of alcohol, their attention is divided, meaning they have a hard time concentrating on more than one thing at a time.

For instance, an impaired driver might be able to keep his or her vehicle traveling in a straight line, but might be driving much slower or much faster than the posted speed. That same driver might also forget to use turn signals or to turn on headlights.

Or a driver could be traveling at the speed limit, but might cross the center line or the fog line.

So while he’s on patrol, Larsen looks for these types of minor infractions that could signal an impaired driver.

Last Friday, he stopped several vehicles for simple traffic violations.

At 8:24 p.m., Larsen stopped a vehicle which failed to use its turn signal when turning onto Highway 20.

At 9:01, he stopped a vehicle for traveling 10 miles over the speed limit.

At 9:58, he stopped a vehicle for traveling with only its fog lights on.

At 11:21, he stopped a vehicle for driving erratically — taking a corner very wide, then cutting across the center line after making a sloppy turn onto Highway 20.

Though he’s looking for simple traffic violations, Larsen said he generally won’t pull over a vehicle for a crossing the fog line once. Ideally, Larsen said, he’s looking for multiple violations over a period of one or two minutes. Which means a driver would have to cross the fog line or center line seven or eight times, or consistently have trouble driving at the speed limit.

For example, Larsen cited a DUI arrest he made Thursday evening. Larsen noticed that after the driver had made a left turn, his turn signal remained on for several hundred feet and he crossed the centerline several times.

Unfortunately, Larsen said, some impaired drivers do drive fairly well. And unless the driver commits an actual traffic violation, there’s no cause for him or her to be stopped. Larsen said traffic laws are in place for that reason. A driver can’t just be pulled over because a trooper thinks the person is drunk.

Larsen added that in the Washington court system, there needs to be enough evidence for a DUI stop to stand up to scrutiny. He said he won’t stop a vehicle on suspicion of DUI unless he feels that he has seen enough evidence of impaired driving — in the form of multiple traffic violations — to present a good case to a jury should the case go to court.

One traffic stop, at 11:27 p.m., raised Larsen’s suspicions enough that he asked the driver to perform two field sobriety tests.

Larsen noticed the car driving with a headlight out, and pulled the driver over to “have a talk.” When he spoke with the driver, he noticed that the man seemed lethargic, and that there was an overpowering smell of cologne emanating from the vehicle. Larsen said some drivers often use perfume or cologne to mask the smell of alcohol.

The driver passed the nystagmus horizontal gaze test, as well as the one-leg stand test, and Larsen sent him on his way.

DUI arrests and crashes unfortunately tend to happen frequently, but there are still incidents that stand out in Larsen’s mind. One, several years ago, happened at the State Patrol’s Burlington office, near exit 231 off Interstate 5. Larsen said an impaired driver speeding on Chuckanut Drive failed to negotiate the curve near the State Patrol office. The driver’s vehicle crashed through the door of a garage near the road, came out the side of the building and ended up upside down in front of the main office.

More recently, Larsen made a DUI stop and arrest on Halloween night. The driver was clad in a full Star Wars Storm Trooper outfit, complete with light saber.

“Asking him to do field sobriety tests in that costume, it was very difficult for me to maintain a straight face,” Larsen said.

And while some people may think it’s rather boring to drive around Whidbey Island all day, or all night, Larsen has just one thing to say: “It can go from sheer boredom to sheer terror in seconds.”

Fortunately for drivers, State Patrol troopers will always be there to make sure the roads are safe, particularly during the holiday season.