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Ala. PD uses 3D scanning to document crash scenes

The scene is preserved for as long as the police department needs it, even to use as evidence in a court case

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By Ben Nunnally
The Anniston Star, Ala.

OXFORD, Ala. — The car might have been nice once, before its driver twisted it into a heap of metal and plastic that came to rest on an Oxford roadway.

He’d been on the run from the police, said Lt. Don Ridley, a crash scene reconstructionist for the Oxford Police Department, going over a video from a past crash scene Friday afternoon. The driver’s guardian angels must have fought hard to keep pace with his vehicle; the wrecked mass tells a story of certain doom, but he survived the crash, Ridley said.

But none of the footage is real — not in the sense we’d think, anyway. This footage came not from a camera but a laser scanning device, a 3D modeling rig from Florida company FARO, which fires off millions of laser beams in every direction. The device records the distance each beam travels before it hits something — leaves, buildings, curbs, cars — and uses the data to make a hyper-detailed virtual model.

Ridley said he put it in about 10 spots around the wreck that day. Each time the machine fires, it also snaps high-definition images and matches what it sees to the laser points. Each blade of grass is rendered in loving detail, as are cracks in the road asphalt and local businesses. Gas cost $1.62 that day at a station beside the wreck.

If he needs to, Ridley can open the scanner file and take anyone to the wreck site to look around in real-time. The scene is preserved for as long as the police department needs it, even to use as evidence in a court case.

“We could put a scaled-down version of a scene on a thumb drive and could give that to the prosecution, the defense — we could even make a copy for everybody on the jury,” Ridley said.

‘It’s hard to beat a laser beam’

Ridley, a shift commander at the police department, has been in law enforcement for 22 years, as of last month. He has been a crash reconstructionist since 2004. He volunteered for the work shortly after joining the Oxford police, having wanted to become a crash investigator for several years.

“I remember where the spark was,” Ridley said. “We had a really bad wreck while I was working in Weaver, on Alabama 21 southbound, just north of the Sports Nut.”

Two drivers had been racing each other late at night, and one lost control, Ridley recalled. The teenage driver of that car died in the wreck. While Ridley held the scene, a state trooper responded to the call (Weaver didn’t work crashes outside its city limits), and Ridley watched the trooper take pictures, mark off the vehicles and collect the data he would later use to figure out what happened.

“I realized, ‘He’s using science to figure out this crash,’ and prior to that moment in time, I didn’t really know anything about that,” Ridley said. “So I started researching what schools you need to go to.”

Weaver hadn’t had any fatal wrecks during Ridley’s time with the department, making the cost of training a reconstructionist impractical. When Ridley joined the Oxford police, though, then-Lt. Bill Partridge was working crash reconstruction, and he was happy to help Ridley pursue the education.

Tools weren’t so sophisticated at the time; measuring tape had yet to be supplanted by laser scanners.

“We had to get out in the road with measuring tape, but it’s dangerous, it takes a long, long time, and it’s accurate, but it’s hard to beat a laser beam,” Ridley said.

Crunching the numbers

The modern software and hardware allows Ridley to create realistic reenactments of crashes; models standing in for real vehicles are placed inside one of the scanner’s 3D environments, and Ridley simulates their head-on collision on a rural road, taken when the department helped another agency figure out a wreck.

Even though displaying the data has gotten easier over the years, the core of the work still comes back to pencil, paper and a book of physics formulas purpose-written for crash reconstructionists.

There are three levels of expertise for crash scene investigators, starting with basic training at a police academy. That education allows a patrol officer to manage fender-benders and the bulk of traffic situations. Then there are traffic homicide investigators, like the trooper who set Ridley’s mind on working crash scenes. They have more advanced training than patrol officers, but stop short of the extreme details. Finally, there are crash reconstructionists, the final word in crash investigation, which Ridley likens to “CSI” for car crashes. They work in trigonometry, sines, cosines and dozens of other terms in the language of educated folk.

That’s why Ridley can wax poetic about kinetic energy the way others might talk about guns, cars and guitars. He can explain why an off-center collision — when vehicles hit each other head-on but about 50 percent off-center — is one of the worst. “Since the center of masses are not aligned, it has a rotational aspect to it, so the vehicles will spin with the energy of the impact … It’s very hard on the human body.” He can discuss the conservation of linear momentum — “We all know the cliche joke that it’s not the fall that kills you, it’s the sudden stop at the end” — and dozens of other consequences of taking speed, mass and deceleration to their limits.

‘Why this wreck happened’

Every investigation begins the same way, despite the myriad physical possibilities in any crash: Start at the end and work backward.

“You start with what you know first, and one thing we know when we first show up is where the crash ended,” Ridley said. “We know the vehicles are going 0 mph at the end.”

Then it’s a matter of following the clues. Skid marks show how far the vehicle traveled with its brakes stomped and wheels locked, which reveals how fast it was traveling. Velocity turns into feet per second, and now Ridley can say about how far back someone was when they reacted to the other car or pedestrian in the road.

Ridley broke down a diagram of a scene from some time ago, when a young child was killed after being struck by a car in front of his house. Ridley reconstructed the scene and was able to show that the driver had been traveling at the speed limit, had braked once the child was visible and that a large tree and a huge dresser left on the side of the road had hidden the boy from the driver’s perspective.

For the driver and the family, knowing what really happened — being able to understand a tragedy — can make all the difference, Ridley said.

“To be able to sit down with a family member and bring closure to them, ‘This is why this wreck happened, this is what I found,’ sometimes we have that opportunity,” Ridley said.

NEXT: Integrating laser scanning and UAV data gives investigators a new 3D view

Bearing bad news, bringing closure

Science and logic make up the procedure, but human connections are still at the heart of Ridley’s job, and the jobs of other officers like him. He’s been the one to explain what caused fatal wrecks to grieving families, offering them answers, and hopefully closure, on their worst days.

He was called on to deliver a death notification once, in 2016, an experience that still sits with him. A 19-year-old woman was hit by an oncoming vehicle — an off-center collision, Ridley said — in her lane. The coroner was unavailable that day, and asked Ridley to speak to the family in his place.

Ridley waited outside the family’s home for about an hour for the woman’s parents to get there. Family members began to arrive and demanded to know what had happened. Ridley said he understood their desperation, but he held his ground, intending to tell the woman’s mother directly. Ridley had been at the crash scene, he said, and had seen the wreck firsthand.

“I didn’t want her mother to hear that from anyone else on the planet other than me,” Ridley recalled.

The woman’s stepfather arrived and also demanded answers. Once the mother arrived, Ridley was able to tell her what happened. She was devastated, he said.

A few weeks later, he received a handwritten letter from the mother, and a photo of her daughter from a few weeks before the crash. She wrote in the letter that she had appreciated Ridley’s effort in notifying her, and said the picture was to ensure that he would think of her daughter as she really was, before the wreck.

“I have a grown daughter,” Ridley said. “I can’t imagine going through it, and I couldn’t imagine somebody coming to my home to tell me.”

The officer said he hoped people could learn more about what goes into investigating a crash scene, and the lengths that crash reconstructionists like him will go to in pursuit of answers, closure and accountability. As an example, he mentioned a recent crash in Oxford, one in which a young girl died and a driver from another vehicle could be charged with murder.

“We’ll move heaven and earth and turn over every rock to figure out why that crash happened,” Ridley said.

©2020 The Anniston Star (Anniston, Ala.)