A dozen police officers were struck and killed while standing outside their cruisers last year across the United States.

But that number represents a dramatic decrease from 2008, when 18 law enforcement officers were hit and killed by cars.

The reason? "Move Over, Slow Down" laws now in effect in 47 states including Ohio, Kentucky and Indiana.

The laws require drivers to move over at least one lane when they see an emergency vehicle with flashing lights on the side of the highway. If they're on a road with only one lane in each direction, or the drivers are unable to move over safely, they must slow down when approaching the stopped emergency vehicle.

The Ohio law was passed more than a decade ago. Yet the Ohio State Highway Patrol reports 196 of its cruisers were struck while stationary in just the last four years. Thanks to a public relations campaign, the OSHP was able to reduce those crashes by nearly 50 percent in the past year.

"There are officers out here that are getting killed because of people not moving over," says Sgt. Christopher Wood. The Ohio trooper should know -- he was nearly one of the statistics himself.

"I heard squealing tires," recounts Sgt. Wood. "I looked to my left and I saw an out of control car coming my way."

The camera on his cruiser's dash board captured the crash that followed on a cool March day in 2002. He had stopped along I-71 to back-up another trooper. He stopped for a brief moment on the side of the highway to adjust his jacket -- a decision that saved his life.

A driver lost control and slammed into the other trooper's cruiser while Sgt. Wood was standing right next to it. The force of the crash slammed the cars into the guardrail, and forced the cruiser's trunk violently into the air.

Sgt. Wood was standing so close to the impact zone, the flying trunk lid knocked off his Stetson. "I mean I was within inches of having a very serious head injury," says Wood.

He did require knee surgery, but Sgt. Wood fully recovered from his injuries.

Wood says, "a lot of people in the public don't have the knowledge of the Move Over, Slow Down law."

AAA has worked to add tow trucks to the existing laws. The auto club has lost tow truck drivers in similar crashes. Currently 38 states include so-called "amber light" vehicles in their Move Over, Slow Down laws.

"There's absolutely no margin for error whatsoever," says Kentucky State Police Trooper Rick Saint-Blancard. "You get people that are on the phone, they're changing CDs, and oh by the way, add the fact that they have their lunch on their laps. So they're looking down trying grab their lunch, multi-tasking. And I tell you those are the root causes of why we have issues on the side of the road."

In addition to distracted drivers, police are also exposed to rubber-neckers speeding by them. Experts say your hands subconsciously tend to follow your eyes. If you look at the flashing lights or the vehicles on the side of the road, you're more likely to steer in that direction.

Even a slight error can be catastrophic at highway speeds. The many frightening dash-cam videos used in our story show crashes where all the victims survived. There are many more crashes that we simply can't show you because the officers or others were killed.

Most of these roadside crashes could have been completely avoided if passing motorists had just moved over one lane, or reduced their speed.

"If people would just practice common courtesy," says Wood, "there wouldn't be a need for some of these laws."