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Police accident-reconstruction experts are taking advantage of a device in new General Motors and some Ford cars that records engine and brake activity in the seconds before, during and after impact.

It's similar to the so-called "black box" on an airplane that records what was happening before a crash, said Ontario Provincial Police Constable Vince Gircys.

The "automobile event data module" was designed as the brain behind the air bag. It decides if the deployment system should activate, depending on whether the impact is a pothole or a crash.

"It's a computer, separate from the car's computer," Gircys said.

The recorder stores information on the car's velocity, its engine RPMs, how far the accelerator pedal was pressed and whether the brakes were applied, seat belts were buckled and warning lights were on, starting from five seconds before impact, he said.

But one of its most important features is that it records the delta V, or the car's change in velocity, which shows the force of impact.

"If you're going 60 mph and strike a concrete wall, within milliseconds the car will go from 60 mph to 0, producing a high delta V," Gircys said.

This is useful because officers can't always tell from looking at a crash scene what took place. "Often we have to reconstruct a scene without anybody left alive," Gircys said.

He added that even if there are survivors, eyewitnesses are often "less than accurate."

Gircys used the Ontario Provincial Police's new crash data retrieval system in a recent inquiry into a 2-year-old fatal crash on the Garden City Skyway in St. Catharines.

In that case, the driver pleaded guilty to careless driving, and Gircys used the retrieval system as part of a coroner's inquest that took place after the charges were resolved.

"Some people put a Big Brother spin on (the data recorder), but to get access to it we need a criminal code warrant, much as if we wanted to get medical records," he said.

The OPP is the only law enforcement agency in Canada with the retrieval system, he added.

James Kerr, program coordinator for the crash data retrieval system at Vetronix Corp., the California company that makes the decoder, said the product has been on the market for about a year.

Since then, he said, it has been used by police around the United States, including state troopers in Massachusetts, Georgia and New Jersey and local police in San Jose and Thousand Oaks, Calif., and Boon County, Ky.

The recorder is installed in about half of GM's 1999 models and almost all its 2000 and 2001 cars, he said.

The information remains in its memory for 250 engine cycles (each time the car is turned on), "which is about 60 days for the average car," he added. It can't be erased unless a serious accident overrides it.

Both GM and the U.S. National Highway Traffic Safety Administration say the recorder is a useful tool for designing safer cars and highways.

Ford is also putting crash data recorders into its cars, Kerr said, but so far, the company insists on doing all the downloading itself.

Vetronix's retrieval system sells for $2,495.

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