On a recent afternoon, Deputy Trey Arnold with the Douglas County Sheriff's Office walked back to his patrol car from a vehicle he'd pulled over on Interstate 25 in Castle Rock.

By the front bumper on the driver's side of his car he stopped, raised both hands in frustration and shook his head at passing drivers.

Several vehicles whizzed by in the lane closest to him, all failing to obey Colorado's "Move Over" law and yield to Arnold - despite having room to switch lanes.

It was an ironic day to break the law.

Arnold was part of a special campaign Dec. 1 spearhead by the Greenwood Village Police Department in which law enforcement was actively enforcing the state's Move Over law to educate the public.

The campaign was months in the planning, but expedited and expanded after a Colorado State Patrol trooper was struck and killed Nov. 25 by a passing motorist when he had stopped to investigate an accident on I-25.

A few traffic stops earlier, Arnold saw a similar situation almost unfold.

Arnold, who stopped a vehicle along I-25 south of Castle Rock, walked back to his patrol car. Partway there, a truck pulling a cargo trailer blew by, leaving mere feet between the vehicle and Arnold.

He got in his car, buckled up and took off after the truck, swiftly maneuvering between other drivers.

Down the road Arnold saw his partner, Deputy Felix Claudio, who had pulled over a driver that failed to yield during Arnold's stop.

"I bet he does the same thing to my partner," Arnold said about the truck he was following.

Sure enough, he watched the truck and trailer stay in the far right lane without attempting to merge to the left or slow down.

Arnold and Claudio were two of four Douglas County Sheriff's Office patrol officers who participated in the enforcement campaign. Other agencies included the Arapahoe County Sheriff's Office, Denver Police Department and the Lone Tree Police Department.

LED road signs above I-25 warned travelers Dec. 1 that enforcement was taking place. Violators were both ticketed and educated on the law.

Revised statute 42-4-705 requires drivers to move at least one lane over when passing an emergency vehicle or vehicles such as maintenance and tow trucks that are parked with their lights on. If a driver can't move over, they must slow to a safe speed.

"As long as they're going slower and they put on their signal in an effort to move over, we understand," Arnold said of those who are unable to merge.

However, slowing to 60 mph in a 65 mph zone doesn't cut it, despite how one driver who Arnold stopped tried to argue.

During the enforcement, Arnold and Claudio played a game of leapfrog. One would make a traffic stop while the other parked behind, ready to pursue drivers who ignored the law.

If one left to make such a stop, the other would catch up and park behind, waiting for the same scenario.

Cmdr. Eric Schmitt with the Greenwood Village Police Department said the campaign got "extremely positive feedback" from other agencies. The department plans on conducting the campaign once a month and, hopefully, recruiting more agencies.

Although the Colorado State Trooper Cody Donahue's death wasn't the original reason for the campaign, it got people paying more attention and provided a timely reason to execute the plan.

"It is extremely important," he said of the Move Over law - not only for law enforcement but also for other types of roadside crews.

Sgt. Rob Madden, spokesperson for the Colorado State Patrol, said it's important for everyone's safety that drivers are reminded of the law.

"Move one lane or slow when approaching emergency, safety, maintenance or courtesy vehicles along the road," he said. "Our job is inherently dangerous and we appreciate when motorists give us room to do our job safely."

On his way back north, Arnold stopped where Donahue was struck and killed, near the Tomah Road exit just south of Castle Rock.

The shoulder left little room for a person to stand either on the driver's side, nearest the road, or on the passenger's side between the vehicle and the guardrail.

He explained how officers' minds run a million miles a minute during a roadside stop. They don't know whom they've pulled over or their intentions, and they must also watch the traffic behind them.

"There are days I go home and, mentally, I am just exhausted," he said.

And yes, he's nearly been hit himself, said Arnold, who has been on the job about 10 years.

Arnold and Claudio were among the officers who responded to Donahue's accident.

"So, it's pretty personal for us," Arnold said of the Move Over campaign. "It's always hard when you go to fatals, but especially when it's one of your own."