By Julie Watts

SAN FRANCISCO (KPIX 5) — Deadly crashes involving large trucks are on the rise. But a simple fix could save lives.

When a test car crashes into the side of a tractor-trailer at just 35 miles per hour, it slides underneath, smashing the heads of the dummies inside — directly into the truck.

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But in a second crash test, the Insurance Institute for Highway Safety has equipped the tractor-trailer with “underride guards” on the side of the truck.

And the outcome is much different.

David Zuby, the executive vice president & chief research officer at the Insurance Institute for Highway Safety said, “It prevented the car from going underneath and consequently the airbags and seatbelts were able to protect the driver dummy in those crash tests.”

While federal law requires large trucks to have rear underride guards, it does not mandate the same protections for the sides of trucks.

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More than 1,500 people were killed in collisions with a tractor-trailer in 2015.

More than 300 of those involved the side of the truck.

Zuby said, “We can’t say for sure how many people would be saved, but if you prevented the car from going underneath the trailer many more people would be alive.”

The institute hopes its crash tests will prompt truck carriers to outfit their fleets with side underride guards as well.

But in the meantime, it’s important for drivers to be mindful around big-rigs.

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Experts suggest leaving extra space between you and big trucks and keep in mind that they have large blind spots.