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Hernando Today

Piecing Together A Traffic Crash

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By KYLE MARTIN

Hernando Today

Published: February 7, 2009

To the untrained eye, a traffic crash is a jumble of twisted metal and scattered debris.

But there is a way to untangle this chaos. You just have to know where to look.

It might not match the flash and panache of TV's CSI, but forensics plays a large role in piecing together a traffic crash. That's especially true for hit-and-run collisions or fatal crashes, says Sgt. Steve Gaskins, spokesman for the Florida Highway Patrol.

Start with big evidence. Unless it's a single-car crash, there are specific clues tied to each vehicle involved. Paint transfer, for example, occurs when cars rub (or smash) into each other. This is useful for pinpointing who hit whom and where.
Tire width and tread is generally unique to the vehicles involved. Consider it like a path to follow into the point of collision.

The driver's injuries can also speak volumes. Sometimes there's conflicting testimony as to who was behind the wheel. But if there's a "starburst" shatter on the windshield and one witness has a big gash on his forehead, it's a fair guess which person will be getting the ticket.

Sometimes clues are more subtle, though. For traffic homicides especially, investigators will rope off an intersection and take hours to comb over every detail.

"We treat it like a crime scene because there's always the possibility someone will be arrested," Gaskins said.

Investigators collect DNA evidence such as hair and blood from the seats. The skin cells left behind on the air bag are a dead giveaway of the driver's identity. In the case of a hit-and-run involving a pedestrian, flecks of paint from the vehicle are usually embedded on the skin and clothing of the victim.

Calculating speed is trickier. As a general rule, if the person rolls onto the hood or windshield, the vehicle is traveling a minimum of 35 mph. If the victim is tossed over the hood, the driver was traveling at least 50 mph.

Narrowing it down from there requires factoring in the surfaces involved in the crash. For instance, if a car leaves the asphalt, crosses a grassy median, then barrels into a car in the opposite lane, there are three surfaces involved.

A car will come to a much quicker stop on the pavement versus the grass because of the friction between the tires and the road, Gaskins explained. To get an idea of how fast the vehicle is going, investigators determine how long it took for the object to slow down.

It all goes back to Sir Isaac Newton's third law of motion: For every action there is an equal and opposite reaction. This can be applied in general terms to the impact every passenger feels in a head-on collision. When two cars traveling 50 mph slam into each other, the force is equal to 100 mph, Gaskins said.

That puts significant stress on the organs of the body. That's why people can walk away from a crash without a scratch, then collapse and die from heart failure, Gaskins said.

The lesson: Obey the speed limit.

"If people would do that there would be fewer accidents and the injuries would be less severe," Gaskins said.

Reporter Kyle Martin can be reached at 352-544-5271 or kmartin@hernandotoday.com.

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