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NHTSA side underride analysis slammed by safety, insurance advocates

NTSB, IIHS say feds significantly underestimate lives that can be saved

IIHS test of an "AngelWing" guard preventing underrides. (Photo: IIHS)

WASHINGTON — The Biden administration is severely underestimating the number of lives that would be saved by truck side underride guards, according to safety and insurance groups, which could block the rollout of a proposed rule mandating such equipment.

In an Advanced Notice of Proposed Rulemaking published in April, the National Highway Traffic Safety Administration estimated that 17 lives would be saved and 69 serious injuries would be prevented each year if underride guards were installed on all trailers under a new standard.

NHTSA also stated that, on a per-trailer basis, the lifetime costs of equipping new trailers and semi-trailers with side underride guards is “six to eight times” the estimated safety benefits. A proposed rule that cannot show benefits outweighing costs would have little if any chance of passing a federal review.

That benefit shortfall alarms the National Transportation Safety Board (NTSB), which contends NHTSA’s analysis focused only on crashes in which the front of a passenger vehicle slides under the side of a trailer. NHTSA did not fully consider other crash types that would likely benefit from side guards installed on a truck that could prevent such an “underride,” according to NTSB, such as high-speed sideswipe crashes, impacts with vulnerable road users such as motorcyclists, cyclists and pedestrians, or side underride collisions with single-unit trucks.


“Further, NHTSA only calculated potential safety benefits for about 20% of fatal crashes in which NHTSA estimated that the passenger vehicle was traveling under 40 mph,” wrote NTSB Chair Jennifer Homendy in comments filed in response to the proposal. “For crashes where the estimated speed was over 40 mph, NHTSA’s analysis assumed that a side underride guard would have no effectiveness.”

The Insurance Institute for Highway Safety (IIHS), an independent nonprofit whose members include major auto insurers, was just as explicit.

“[IIHS] believes NHTSA’s analysis suffers from several fundamental flaws that reduce its benefit estimates for side underride guards,” wrote IIHS Senior Research Engineer Matthew Brumbelow. “Specifically, we estimate the number of lives that could be saved by a side underride guard standard is up to ten times the number reported by NHTSA.”

Asked to comment further, Brumbelow said NHTSA’s decision to move forward with a rulemaking “will largely depend on their cost-benefit analysis, so if they’re underestimating it by a factor of ten, it greatly reduces the chance they would pursue” such a rulemaking, he told FreightWaves.


IIHS’s concerns with NHTSA’s analysis centered on overly restrictive criteria used to identify fatal crashes, problems establishing whether or not an underride occurred in specific crashes that NHTSA analyzed, and “a misunderstanding of the relationship between crash severity and pre-crash travel speed,” according to Brumbelow.

Homendy and Brumbelow called on NHTSA to provide a more thorough cost-benefit analysis that does not depend on multiple assumptions of costs and benefits.

“Large truck side underride crashes result in hundreds of lost lives and debilitating injuries each year,” Brumbelow stated. “Equipping trailers with side underride guards would immediately and significantly reduce this unacceptable toll.”

Trailer makers: Benefits overstated, not understated

Trailer manufacturers, which would have to raise the price of new trailers by $3,740 to $4,630, according to NHTSA’s estimates, to comply with a side-guard mandate, agreed that the agency’s analysis is flawed — but because safety benefits are overstated, not understated.

The Truck Trailer Manufacturers Association (TTMA), whose members manufacture most of the heavy-truck trailers used in the U.S., argued that because more trucks would likely be needed to adjust for the weight displaced by the equipment (to stay in compliance with highway weight restrictions), more lives would be lost from other accidents caused by having more trucks on the road unrelated to side underride accidents. A side underride guard mandate would put more lives, not fewer, at risk, the group asserted.

“TTMA would support the implementation of [side underride guards] if they ever become both justified and technologically feasible,” wrote TTMA Engineering Manager John Freiler. “At this time, it would seem that other regulatory action and research into advanced driver assistance technologies promise a much greater chance to reduce side collisions into trailers as well as other types of crashes.”

NHTSA extending comment period

NHTSA received petitions from the American Trucking Associations and underride guard safety advocates requesting that the comment period on the notice, originally scheduled to end June 20, be extended to provide more relevant and updated crash data. On Thursday NHTSA said it would extend the comment period by 30 days.

“NHTSA agrees that allowing additional time for the public and its stakeholders to provide robust and substantive comments on this complex issue will better inform NHTSA,” the agency stated.


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John Gallagher

Based in Washington, D.C., John specializes in regulation and legislation affecting all sectors of freight transportation. He has covered rail, trucking and maritime issues since 1993 for a variety of publications based in the U.S. and the U.K. John began business reporting in 1993 at Broadcasting & Cable Magazine. He graduated from Florida State University majoring in English and business.