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ARLINGTON, Va., (WUSA) -- It's a scary combination, a car colliding into the back of a semi-trailer at highway speeds.

So called underride crashes can leave passengers susceptible to severe head and neck injuries, even death, when the top of the car is crushed.

New tests of eight types of semi-trailers by the Insurance Institute for Highway Safety found that most underride guards do a decent job of preventing passenger cars from sliding underneath it in a crash.

Still, IIHS tests found that a certain type of crash that involves the outer edge of big rigs could put people in greater danger.

"The typical underride guard is suspended from two vertical components hanging relatively near the center of the truck. That means that the part of the guard that sticks out toward the ends of the truck, doesn't have a lot of support," says David Zuby.

But there is good news. Many trailer manufacturers have been installing underride guards that are even stronger than U.S. guidelines require.

IIHS Underride Guards Crash Tests

And, the number of passengers killed in accidents where the front of the vehicle struck the rear of the truck has dropped over the last decade.

The Insurance Institute for Highway Safety is an independent organization that is funded by the insurance industry.

Its data does not track how many of these front-vehicle to rear-truck crashes specifically involve underrides.

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