Even if you buckle up for safety you could be at deadly risk from someone riding with you.

KIRO 7 Eyewitness News Health Reporter Micki Flowers has results of local research that could save your life.

You may think you're protected because you fasten your seatbelt every time you get in the car.

But a study by Harborview Medical Center researchers shows it could be a huge mistake to ride along with someone else who won't wear a seatbelt.

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Most people know buckling up could save your life.

Sue Dynneson Bynun says she's not shy asking her passengers to do the same.

"It's me who's driving the car. I'm responsible for them," said Bynun.

Crash test dummies graphically show another reason to ask those unbelted riding companions to strap in.

They catapult around the car in a wreck. And new research shows how often unbelted riders can become lethal weapons.

Researchers at Harborview Medical Center looked at more than 60,000 fatal car crashes between 1988 and 2000 to determined the risk.

"Even if you're restrained, if there's somebody else in the car with you who is not wearing a seatbelt, it increases your risk of death by 15 to 25 percent," said Dr. Fred Rivara, Harborview Injury Prevention and Research Center.

"That's really frightening, actually, to think that someone that you just ignored because they didn't buckle up could actually put you at death's door," said Bynum.

And according to the new findings, it did not matter where the unbelted person sat in relation to the person wearing a seatbelt. What mattered most was that someone, somewhere in the vehicle wasn't strapped in.

"The bumper sticker message is, 'Wear your seatbelt and have everyone else in the car wear their seatbelts as well,'" said Rivara.

The warning sounded by this study is all the stronger when you consider this: Motor vehicle crashes are the single most common way people die from injuries in the United States.