“Requiring side underride guards could save more than 10 times as many lives as NHTSA projects,” said IIHS Senior Research Engineer Matthew Brumbelow. In 2021, there were 488 passenger vehicle occupant fatalities in crashes involving the side of a tractor-trailer.

During an underride crash, a smaller vehicle crashes into a truck and goes completely or partially underneath it. This makes serious injuries to people riding in the smaller vehicle more likely.

NHTSA requested comments on its preliminary cost-benefit analysis of requiring side underride guards on all new trailers and semitrailers. The report estimated that equipping all large trucks in the U.S. fleet would cost between $973 million and $1.2 billion and would prevent 17 fatalities and 69 serious injuries annually.

Using what IIHS called “an alternative method,” Brumbelow projected that a side-underride guard mandate could prevent ~159-217 passenger vehicle occupant fatalities per year, depending on whether it required protection forward of the rear axle or along the full length of the trailer. It would also “likely save many of the pedestrians, bicyclists and motorcyclists who are killed each year in crashes involving the sides of tractor-trailers.”