(Bloomberg) -- The U.S. National HighwayTraffic Safety Administration is proposing that truckingcompanies be required to install stronger guards on their trailersto reduce deaths caused when cars rear-end tractor trailers.

The agency said Monday that underride guards, which have hungdown from the back ends of box trailers for decades, should bestrong enough to protect passengers in crashes of up to 35 milesper hour, an increase from the current 30 mph standard.

“Robust trailer rear-impact guards can significantly reduce therisk of death or injury to vehicle occupants in the event of acrash into the rear of a trailer or semitrailer,” said MarkRosekind, administrator of the safety agency. “We’re always lookingat ways to safeguard the motoring public, and today’s announcementmoves us forward in our mission.”

The agency is trying to reduce the number of people killed orinjured in underride crashes. When cars go under a truck trailer ina rear-impact collision, severe head damage or even decapitationcan result. The agency has estimated there are about 400 deathsfrom cars hitting the backs of trucks each year, with about 125 ofthem resulting from severe damage from objects intruding into inthe passenger compartments.

Canadian standard

NHTSA’s proposal would adopt the same requirements used inCanada. The agency estimated the industry would need to spend atotal of $13 million to meet the new trailer standards. NHTSA willaccept public comment for 60 days before issuing a finalregulation.

About 93% of the truck trailers currently sold in the U.S. willmeet the new requirements, NHTSA said. The incremental costs forequipping new trailers with stronger guards will be about $229, andthe expected cost for the industry as a whole will be $13 million,the agency said.

“While we are still reviewing today’s announcement, underrideguards like the ones envisioned by NHTSA’s proposal have been inuse in the U.S. and manufactured here for some time,” Sean McNally,a spokesman for the American TruckingAssociations, said in an e-mailed statement. “While we believethe best underride guard is still the one that doesn’t need to beused, ATA is optimistic this proposal will be a step forward forhighway safety.”

The Arlington, Virginia-based Insurance Institute forHighway Safety petitioned NHTSA for a stronger underridestandard in 2001, after testing bars on trailers built by threecompanies to federal standards. Cars with crash-test dummiesslammed into the bars, which buckled or broke in several tests. Thetrailers often broke through the windshields.

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Tests the insurance institute conducted showed some trailerguards that met Canadian regulations didn’t perform well when carscrash into them at an angle, said David Zuby, chief researchofficer for the group. Many manufacturers already are designingguards that are stronger, he said.

“The data we submitted suggested the agency could go beyond theCanadian standard,” Zuby said.

NTSB recommendation

Marianne Karth, a North Carolina mother who lost two daughtersin a 2013 truck crash, also petitioned NHTSA for a strongerunderride guard, as did the Truck SafetyCoalition, an Arlington, Virginia, group that lobbies forstronger regulations. Karth and the group met with TransportationSecretary Anthony Foxx to discuss the issue. The NationalTransportation Safety Board has also recommended stronger guardsafter investigation truck crashes.

“I’m glad to see this step is being taken,” Karth said in aphone interview. “I’m hoping everything will be done to make theseguards as strong as possible. A whole lot more can be done thanjust meeting the Canadian standard.”

The stronger guards will prevent between one and three seriousinjuries and one fatality a year, NHTSA said.

Safety groups have questioned whether NHTSA’s analyses arepicking up all of the relevant deaths in underride crashes. Theagency seems to be “significantly underestimating the benefits ofan improved rear guard,” said John Lannen, executive director ofthe Truck Safety Coalition.

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