THE SCENE TELLS THE STORY
Math, models are tools of trade for crash investigators
BY NATALIE STEWART ENTERPRISE STAFF
HIGH POINT — Tires squeal across the pavement. Then comes the loud boom of an airbag deploying and metal crunching. Glass shatters and sprays across the roadway.
Then sirens wail, and crash investigators start piecing together what happened.
By the end of the investigation, police know the details of each moment leading up to the impact. They know at which instant the the driver in each vehicle should have seen the other. They know the speed the vehicle was going before the crash, the moment the driver reacted and the speed at impact.
‘THE SCENE ALWAYS TELLS A STORY’
Jeffrey Crouse and Pete Abernethy both have been assigned to the High Point Police Department’s Traffic Unit since 2010. They’ve both investigated countless crashes, and typically work in tandem like a well-oiled machine.
The Traffic Unit is typically called to a crash when it’s fatal or someone has critical injuries.
The first thing both Abernethy and Crouse do is walk through the scene.
“I don’t want a bunch of different opinions coming at me at first because I don’t want that to taint what I see,” Abernethy said. “The scene always tells a story. We want to stand back and take everything in.”
Crash investigators operate in the same manner as homicide detectives, Abernethy said. And sometimes, murder charges are filed in fatal crashes.
Investigators first collect and document “short-lived” evidence — blood marks, tissue deposited on the road and any other biological matter, skid marks, gouge marks from where the metal of the vehicle was forced down into the road.
“(The scene) tells you which car left which marks,” Crouse said. “It tells you which direction the cars were going before they hit and the direction they went after they hit.”
Typically, Crouse said investigators can figure out what happened simply by looking at the scene. Then they start talking to witnesses. As veteran investigators, Crouse said one thing they’ve learned early on is witnesses are sometimes wrong.
Many times, witnesses don’t actually see the moment before impact or even the impact, but they hear the screeching tires and crushing metal and turn to look. From that point witnesses start developing in their minds what they believe happened.
“If a crash happens and you turn around and see something occurring that’s already started, then naturally your brain is going to complete the scenario for you,” Abernethy said. “I really, truly don’t think people intentionally try to throw us off. Your brain wants a complete story, so it fills in the parts you missed.”
Crouse said witnesses are still imperative to the investigation.
‘THE DRIVER IS THE WILD CARD’
There are three elements to every crash — the car, the road and the driver, Abernethy said.
“The science part of the crash is the reconstruction,” he said. “The art form is human behavior and what people do in crashes. The car isn’t going to lie to you, and the road isn’t going to lie to you. The driver is the wild card. It’s the only element that has the ability to lie.”
That’s where the crux of the investigation comes in, because police are taxed with determining who’s at fault. There could be an equipment failure or a roadway issue that leads to a crash; however, Abernethy said that’s rare. The vast majority of the time, human error caused the impact. And traffic investigators don’t call crashes accidents, because if there’s impact, a law was violated, Crouse said.
Each piece of evidence left on the road is critical, and it’s precise point on the earth is measured and documented. Investigators also document each reflector in the road, the roads edges, curb lines and each mark. Thousands of points are documented, and entered into forensic software, where a scale diagram is built.
“We can lay this huge scene out and use that to put scale-size cars on it,” Abernethy said. “Then we recreate how these cars came together and why.”
Police also can create animated videos to use in court, which puts a jury in the car where they can see what the drivers saw before and during impact, Abernethy said.
‘HOW FAST WERE THEY GOING?’
The No. 1 question asked in every crash, Crouse said, is “How fast were they going?”
For that, there is no software program that reveals a vehicle's speed, or a simple way of finding the answer. To find it, the investigators take out their pencils and notepads and do “a whole bunch of math by hand,” Crouse said.
That’s after getting all the pieces to plug into the equation.
“We figure out at what point they hit and where they came to a final stop,” Crouse said. “You get the distance and then you figure out the drag factor.”
The drag factor is the friction between a vehicle and the road, and it changes for the same roadway throughout the day. The temperature at the time of the crash also plays a role. Also the weight of the vehicles.
“Then we take out a notebook,” Crouse said. “One problem could take 10 pages, and that’s just to get a variable to plug into another formula that takes another 10 pages.”
To complete the investigation, it sometimes takes three to five weeks.
“We take everything, every little piece of evidence and information we can get,” Crouse said. “No matter how minor.”
There are times where investigators spent 32 hours straight working to piece together what happened in a crash, but for both Abernethy and Crouse, it’s worth every minute.
The traffic unit recently investigated a hit-and-run where a woman was critically injured, and Crouse said he didn’t think they’d ever find the car that drove away and left the woman lying in the road. But they found it, and they were able to tell the woman’s son the driver was being charged.
“To hear that young man say, ‘I just want to come down there and give them all a hug,’” Crouse said. “That’s worth more than any paycheck. That’s rewarding.”
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