Special Report: Accident reconstruction

After every major accident, state police are on scene investigating.

Sgt. Kerry Alvino from the Massachusetts State Police says, "When you're out there taking your measurements, you risk getting hit by a car. You always have to watch your back.

Like this 10-car accident on I-93 last month. One trooper was injured after pushing a bystander out of the way of oncoming traffic.

Now, new digital cameras and software allow troopers to gather evidence in a fraction of time, and get traffic moving again.

"We're able to take photographs and clear the scene much quicker," says Sgt. Alvino.

It's called photogrammetry, and because it's all digital, only about a dozen measurements and photos are taken on site. Back in the office, the trooper punches in the info and the computer calculates measurements for every element on the scene, including skid marks.

"It can tell us exactly how fast the car was going when it generated those marks on the road."

This data can be fed into another program and a 3D re-enactment takes shape.

Sgt. Alvino says, "This is going to be more helpful to explain how the crash happened, and what the vehicles did."

And in the end, it lowers everyone's risk.

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