New trailer underride guards fall short, safety advocate says

Avatar photo

U.S. regulators are adopting tougher standards for the rear impact guards on trailers, mirroring Canadian rules designed to better protect the occupants of light vehicles at crash speeds up to 56 km/h.

Previous standards were based on speeds of 48 km/h, and the upgraded guards will need to withstand higher forces when a car hits a guard straight on, or when the front half of a car overlaps a trailer’s rear end.

(Photo: IIHS)

“This new rule will improve protection for passengers and drivers of passenger vehicles,” National Highway Traffic Safety Administration (NHTSA) administrator Steven Cliff said in a press release.

Manufacturers must comply with the rules two years after they’re published in the federal register.

But with nine major trailer manufacturers already choosing to adopt the Insurance Institute of Highway Safety (IIHS) stricter ToughGuard standards, safety advocate Marianne Karth describes the mandatory changes as “too little, too late”.

Petitioned change

The new rules are largely the same as those first published in December 2015, added Karth, whose daughters AnnaLeah and Mary were killed in a May 2013 underride crash. “They’re still not doing something I could count on to save my daughters.”

The U.S. Department of Transportation says the rulemaking process was triggered by petitions from Karth and the Truck Safety Coalition, and it responds to a mandate imposed by the 2021 Bipartisan Infrastructure Law.

The Canadian rules have been in place since 2007, and their tougher approach was established to better protect the occupants of sub-compact cars like a 1998 Chevy Cavalier or Honda Civic. Sub-compact cars represented 2.4% of U.S. sales in 1993, but 11% of the Canadian fleet and 22% of the fatalities in crashes involving trucks.

U.S. Federal Motor Vehicle Safety Standards 223 and 224, like their Canadian counterpart, will mean such guards can’t deflect more than 125 mm in crash tests and can’t lift more than 560 mm from the ground.

An estimated 94% of new trailers sold in the U.S. already comply with Canadian Motor Vehicle Safety Standard 223, NHTSA adds. Upgrading the guards to the new U.S. standards will add 48.9 pounds per vehicle.

No rules for 30% offset

But NHTSA decided against a standard that would apply to crashes where just 30% of the car’s width overlaps the rear of the trailer, concluding that available data didn’t show such a standard would be reasonable, practicable, or appropriate for all equipment affected by the rule.

Manac’s rear underride guard passed tests for such crashes because vertical supports are mounted outside the trailer frame rails and attached to a reinforced section of the trailer floor.

“Trailers that have the main vertical supports for the guard more outboard may not perform as well in full overlap crashes as the trailers that have the vertical supports more inboard,” the regulators concluded. “This finding was of key concern because full and 50% overlap crashes are more frequent than low overlap [30% or less] crashes.”

The Insurance Institute of Highway Safety says the final rule “falls well short” of addressing its concerns.

“While the new standard is an improvement over the old one, nearly all newly manufactured guards on trailers already meet this new standard,” IIHS president David Harkey said in a statement, noting its crash tests show further improvements are feasible.

The institute petitioned the federal government in 2011 to improve underride protection, and its research in the early 2000s confirmed more could be done, he added.

“To truly reduce the number of lives lost in underride crashes, NHTSA needs to incorporate changes that would require crash testing of guards when mounted on trailers, allow fewer exemptions for other kinds of trucks, and improve protection in offset crashes.” 

Side guards and reporting

Moving forward, NHTSA will also establish a federal advisory committee to study side impact guards, and it’s calling on states to better track underride crashes with support from educational materials that help police identify and record such situations.

“This is just washing their hands of it and kicking it down the road,” Karth said of the promise for more research, noting that regulators have been committing to that for decades.

But there are clear gaps in the data, she said, noting that her daughter Mary was identified as a “non-fatal injury” following their crash.

She died in hospital four days later.

  • This article has been updated to include comments from IIHS
Avatar photo

John G. Smith is Newcom Media's vice-president - editorial, and the editorial director of its trucking publications -- including Today's Trucking,, and Transport Routier. The award-winning journalist has covered the trucking industry since 1995.

Have your say

This is a moderated forum. Comments will no longer be published unless they are accompanied by a first and last name and a verifiable email address. (Today's Trucking will not publish or share the email address.) Profane language and content deemed to be libelous, racist, or threatening in nature will not be published under any circumstances.


  • Not sure I understand the second paragraph under the “No rules for…” subheading — the reference to Manac and the explanation of those particular design issues. After googling Manac I realize it’s a trailer manufacturer, but there is no earlier mention in this article of what this refers to. Was it the trailer make in Ms. Karth’s daughters’ accident? Also unsure why the headline makes it sound it is “too little, too late” when in fact it brings the US norm to par with Canada’s. The issue seems to be of the partial vs. full-width impact which apparently is dealt with similarly under both sets of rules. Structurally the focus on full-impact accident prevention makes sense, and it is easy to see why the line is drawn at what types of accidents are more common. Unfortunately, it sounds as if the accident in Ms. Karth’s daughters’ case was one of those with less-than-full impact. It is hard, and I feel for her.

    • Manac is a major trailer manufacturer, and its underride guards performed well in tests where just 30% of a car’s front end overlapped the rear of a trailer. But NHTSA expressed concern that regulating similar designs could ultimately affect the way bumpers perform when hit in the middle of a guard. Mrs. Karth suggests that the standards could be even tougher than those that were finalized. The Canadian standards were also in place years before the collision in which her daughters were killed.