Can Conflicting Conclusions in Side Underride Guard CBAs BOTH Be Correct?

What will Congress and NHTSA do with conflicting conclusions from two side underride guard cost benefit analyses? After all, they can’t both be correct, can they? The answer matters for thousands of road users who may otherwise lose their lives in future collisions with the sides of tractor-trailers.

In 2023, NHTSA issued an Advanced Notice of Proposed Rulemaking (ANPRM) for side impact (underride) guards. The cost benefit analysis, which was not externally peer-reviewed, concluded that 17.2 lives would be saved per year, that the annual discounted cost would be between $970 million and $1.2 billion, with a resulting cost per equivalent life saved ranging between $73.5 million to $103.7 million. They therefore determined that a side impact guard regulation would not be cost-effective.

In contrast, Eric Hein, a retired federal scientist, published a double-blind, peer-reviewed cost benefit analysis study in the Journal of Progress in Safety & Security on May 15, 2026, titled, Cost-benefit analysis of side underride guards for new semitrailers in the United States. Hein concludes,

In every modeled scenario, preventing 50 to 150 fatalities and comparable numbers of serious injuries produces positive present value net economic benefits. Estimated net benefits range from $0.137 billion to $2.8 billion and consistently exceed the combined costs of side underride guard installation and the fuel penalty attributable to added weight.

These two one-pagers, created by Hein, summarize the results of his study:

Side Underrride CBA Policy Brief

Side Underride Hidden Legal Costs

Hein’s study was referenced in his recent opinion piece published on June 4 in The Hill, Federal regulators know exactly how to prevent side underride deaths.

NHTSA requested comments on their 2023 Side Impact Guard ANPRM Regulatory Analysis:

The agency requests comments that would help NHTSA assess and make judgments on the benefits, costs, and other impacts of side underride guards to increase protection for occupants of passenger vehicles in crashes into the sides of trailers and semitrailers. This ANPRM summarizes NHTSA’s research and requests comment on the accuracy of the estimated benefits, costs, and other impacts of requiring side underride guards on heavy trailers and semitrailers.

In response to NHTSA’s request for Public Comments, numerous individuals and organizations questioned the accuracy of NHTSA’s conclusions. That included this excerpt from a comment submitted by the Insurance Institute for Highway Safety:

The Insurance Institute for Highway Safety (IIHS) believes NHTSA’s analysis suffers from several fundamental flaws that reduce its benefit estimates for side underride guards. 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. . .

The LTCCS-derived estimates for relevant fatalities are roughly 9-13 times the 17.2 lives NHTSA
estimated could be saved by a standard. Interestingly, the agency estimated the costs of a rule to be “6-9 times as large as the corresponding estimated safety benefits.” Establishing how many of these crashes may overwhelm side guard designs and still allow fatal underride would require higher speed crash testing of different potential designs and a better estimate of real-world crash severity in side underride crashes, including a reasonable distribution of impact angles. Even after applying a realistic upper severity limit for guard effectiveness, the available EDR data suggest a side underride guard regulation would be close to the cost effectiveness threshold established by NHTSA using passenger vehicle occupants alone. The true benefits will only be larger once the agency accounts for the number of pedestrians, bicyclists, and motorcyclists whose lives could be saved by side underride guards.

In conclusion, IIHS believes side underride guards have the potential to save many more lives than NHTSA has estimated in its cost-benefit analysis. We urge the agency to perform a more thorough analysis that does not depend on multiple assumptions that guards will provide no benefit outside a narrow range of conditions. Large truck side underride crashes result in hundreds of lost lives and debilitating injuries each year. Equipping trailers with side underride guards would immediately and significantly reduce this unacceptable toll.

Now that NHTSA has received multiple public comments questioning the accuracy of their cost benefit analysis, what are they going to do? Especially relevant is the Truck Trailer Manufacturers Association (TTMA) 2016 Public Comment related to a 2014 petition for underride rulemaking: