Trooper Matthew Johnson walked up to a white board and started scribbling.

“Let’s say you’re driving your vehicle down the road and you skid here and stop here,” Johnson said, drawing a 2D car, followed by horizontal lines picturing the vehicle’s trajectory.

“That’s 30, a constant, times the distance the car skids, 45 feet, times the coefficient of friction of the road,” he continued, quickly drawing a formula that looked simple enough when he did it.

He turned to his partner, another crash reconstruction specialist at the Wisconsin State Patrol.

“Mike, calculator,” he said.

“It’s 34.74 mph,” Michael Smith replied.

“So we know that the speed here, at the start of the skid, was 34.74 mph,” Johnson finished confidently. “It’s physics.”

Although the exercise was impressive, Johnson said: “That was an easy one.”

Stationed in Waukesha and covering southeastern Wisconsin, Smith and Johnson are one of 13 Wisconsin State Patrol crash reconstruction specialist teams. They are the troopers behind reports that contain vital information on traffic accidents.

Most of their work is done by collecting evidence at accident scenes. They later use that information to determine who was at fault, how fast cars were going, whether the driver broke sufficiently, among other factors.

They also use airbag control or sensing and diagnostic modules—dubbed “black boxes.” These devices record crash information just before airbag deployment.

Most newer cars have them, Smith said. If a vehicle has airbags, it likely has an airbag control module.

National attention was focused on the modules recently after a series of recalls by Japanese automaker Toyota, whose cars had an issue with sudden acceleration. Now, lawmakers in Washington are working on a bill that would require black boxes to be standard.

Recording modules are always activated, but they only record information seconds before airbag deployment. The information varies, but it usually includes speed, braking information, acceleration and deceleration of the vehicle.

The recording modules have been around for a while.

“I prosecuted one about 11 years ago,” said Steve Madson, the assistant district attorney responsible for most traffic prosecutions in Walworth County. “They have been around for quite a while. But now they’re more and more prevalent in cars.”

Smith said legislation in Congress could help crash reconstruction and investigation work. Currently, each automaker has its own device to read the information recorded. Toyotas and Mazdas, for example, are nightmares for crash reconstruction specialists.

“Two years ago, we had a crash involving a Mazda, and we just knew we wouldn’t be able to download the data,” he added.

Currently, the Wisconsin State Patrol can read data from Ford, Chrysler and General Motors vehicles. For other automakers, the State Patrol must request data from the companies, losing ground on investigations and slowing prosecutions.

The bill would make reading instruments standard across the industry, the troopers said.

On the prosecution side, Madson said, it helps to have data obtained from recording modules.

“It certainly is a good indication of the crash analysis,” the prosecutor added. “That is helpful, and it definitely makes a stronger case. But it isn’t fail safe.”

In some crashes, the airbag isn’t deployed, Johnson explained. And when that happens, the system doesn’t record any data.

So for now, Johnson and Smith will continue to be much needed parts of crash investigation in the state scene. Machines are useful to corroborate investigations, but they’re yet to replace human investigators.

“You still need physical evidence and science to supplement the data,” Smith said.

“It’s just like any other mechanical device,” Johnson continued. “It just states data.” does not condone or review every comment. Read more in our Commenter Policy Agreement

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