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State Trooper reconstructs accidents to get answers

Minnesota State Trooper Dion Pederson photographs a crash scene to reconstruct why it occurred. (Sarah Smith / Enterprise)1 / 3
Dion Pederson2 / 3
Dion Pederson's drawing puts some of the pieces of the crash together. (Sarah Smith / Enterprise)3 / 3

Dion Pederson has tiptoed to many doorsteps in the dead of night. There's usually no need for his carefully rehearsed speech. Just his presence at that hour tells the family inside that a loved one that isn't home yet isn't coming home - ever.

That's one of the worst parts of his job as a Minnesota State Trooper. That and coming upon an accident scene where the occupants of a vehicle have been ejected and he finds deceased toddlers still strapped in their car seats.

"These are the ones that get you," he admitted quietly. "Those are hard."

Pederson for the last 13 years has applied his skills as a self-described nerd to reconstructing crashes, hundreds and hundreds of them.

"Families have the right to have an answer," he said. It's important to determine how a crash, not an accident, occurred, to give a grieving family a measure of closure.

By the time Pederson gets to a crash scene, it's too late to prevent it. But he can pinpoint the major cause of the majority of serious and fatal crashes - driver error.

And that's why law enforcement officials target bad driving behaviors such as drinking, speeding and not wearing safety belts.

Pederson's Panasonic Toughbook has many pricey tools loaded on it to help him find the answers to how a crash occurred.

The software gives him mounds of information about any vehicle manufactured in just the swipe of his thumb across a mouse pad.

But increasingly, airbag control modules (ACMs) can unlock the key to a crash cause. Often referred to as "black boxes," the silver squares, also referred to as electronic crash sensors, hold a litany of valuable information.

Pederson starts from the final resting place of the vehicles and works his way backward, to the impact and then further back to the causation.

The five seconds leading up to a crash are crucial to determine what occurred, he said.

"The average human reaction time is one-point-five seconds," he said. And he finds no difference between the old and the young. It's a matter of paying attention to what you're doing.

He starts at the scene and usually insists upon being present. He's been flown to accident scenes elsewhere more times than he can recall.

"If it's important enough for them to call me, it's important that I go to the scene," he said without a trace of ego.

While the injured and deceased are being removed, Pederson's camera and can of fluorescent spray paint are already in action.

Various points of impact and skid marks are always spray-marked in case a reconstructionist needs to re-visit the scene. Gouges in pavement, vehicle parts and the weather conditions are important clues, he said.

Photos are invaluable in showing the damage to vehicles and sometimes the injuries. The injuries can often tell him where a victim was riding in a vehicle if the occupants are ejected.

"We take them (photos) before any paint is put down," he said."

It's a tedious process.

"I'm a crash geek," he admits, having witnessed 1,000 fatalities in his 24 years of law enforcement. He's reconstructed car crashes, motorcycle crashes, crashes with pedestrians and bicycles, some off-road vehicles, trucks and tractors.

Each road surface has a "friction factor."

But no roadway is safer than any other, he maintains. Remember it's human error, not surface error. A four-lane interstate high way can be as deadly as a gravel road if the driver is impaired, speeding distracted, sleepy or on the phone.

"Crashes depend on traffic volume," he said, along with human factors.

He's reconstructed the fatal crash of a former partner, of multiple fatalities.

(And to bolster his credentials, he and wife Sue, also a trooper, are the parents of two teenage drivers.)

No one particular sliver of a crash tells the whole story, so Pederson painstakingly pieces together the clues.

Skid marks that go from a shadow on the road to an all-out black mark tell him when a driver started braking and when the wheels locked up.

"Waking up the data box," as he refers to the ACM, opens up a treasure trove of information.

Was the cruise control on? What speed was the vehicle traveling? He can compare his own math to the ACM's for redundancy or refiguring. Ignition cycles can indicate the car's RPM, its starting speed and what percent of throttle the driver was giving the vehicle.

What was the momentum of the crash? Which way did the car swerve and when? The steering wheel ratio can usually tell him if a driver tried to avoid someone in his or her own lane. When did the airbags deploy?

Aerial photos can be invaluable if the Patrol is able to get a plane in the air, Pederson said.

He maps it all out on the Toughbook.

He's attended numerous school courses in reconstruction using crash test dummies dressed as vehicle occupants.

Students observe where objects such as shoes, hats and sunglasses land on impact, what position the mannequins are in when officers arrive on the scene.

Each items tells a story.

"It's critical not to move anything on the road," he said.

Modern cars are engineered much better than they were even though they're much lighter, Pederson maintains. He has yet to go to a crash scene involving a tiny Smart Car or a hybrid, but he said that day is coming.

Many features of cars are designed to absorb impact, taking the crash energy away from the human occupants, he said.

And as a motorist in traffic, he shakes his head at the signs that indicate what could bring him to someone's porch in the dead of the night, the speed, the inattentiveness, the drivers on cell phones.

"Everybody's in a hurry to go nowhere."

Sarah Smith

Sarah Smith is the outdoors editor. She covers courts, business and breaking news in addition to outdoors events.

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