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The Government Admits It Cannot Count These Deaths

Truck Trailer
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There's a kind of highway death the federal government has conceded it doesn't know how to tally. An underride crash is what happens when a car goes under a tractor-trailer instead of hitting it. The bumper, the crumple zones, the airbags, the safety cage — every system engineered to absorb a collision — gets bypassed, because nothing strikes the part of the car built to take a hit. The trailer arrives at windshield height. These are the wrecks where the roof of a car comes off. People die in them at speeds most drivers assume they'd walk away from them.

Nobody knows the number

In March 2019 the Government Accountability Office published GAO-19-264, Truck Underride Guards: Improved Data Collection, Inspections, and Research Needed.

GAO reported that "from 2008 through 2017, an average of about 219 fatalities from underride crashes involving large trucks were reported annually." Less than 1 percent of all traffic deaths.

Then it explained why you shouldn't trust that figure:

"These fatalities are likely underreported due to variability in state and local data collection. For example, police officers responding to a crash do not use a standard definition of an underride crash and states' crash report forms vary, with some not including a field for collecting underride data."

GAO also found responding officers "receive limited information on how to identify and record underride crashes." Sit with what that describes. There's no standard definition of an underride crash for reporting purposes. Some states don't have a box on the form. Officers aren't trained to spot one. So the 219-a-year number is a count of what got written down by people nobody asked, in any consistent way, to write it down.

GAO didn't offer a corrected figure. It didn't claim to know one. What it recommended was that NHTSA fix the Model Minimum Uniform Crash Criteria to include a standard definition and a data field, train police to identify these crashes, and research whether side guards work — and that FMCSA start requiring rear guard inspection during the annual commercial vehicle inspection.

The back of the trailer: a rule that finally got better

The rear has been regulated for a long time. Federal Motor Vehicle Safety Standards 223 and 224 require the rear impact guard — the horizontal steel bar hanging under the back of a trailer. For years the American standard lagged Canada's and only tested guards in full-width impacts, which meant a car striking the corner of a trailer could defeat a perfectly compliant guard.

NHTSA fixed part of that on July 15, 2022, aligning with the Canadian standard. Guards now have to hold up at 56 km/h — about 35 miles an hour — in both full-overlap and 50 percent overlap configurations. FMVSS 223 traded point-load testing for a uniform distributed load test. Effective January 11, 2023; compliance required by July 15, 2024.

That's a genuine improvement, and it has two limits worth naming.

NHTSA declined to require protection in 30 percent overlap crashes — the outer corners — on cost-benefit grounds, estimating the rule as written would prevent roughly 0.56 lives and 3.5 serious injuries a year while acknowledging 5.8 to 11.5 annual fatalities in low-overlap crashes. On July 15, 2024, the agency denied a petition asking for more. And it's a 35 mile-per-hour standard. Mississippi posts 70.

The side of the trailer: nothing at all

Here's the fact that stops people. There is no federal requirement for side underride guards. NHTSA says so itself in its 2023 advance notice: "There are currently no Federal requirements for side underride guards on trailers." The agency adds that side guards "are not currently required by any country."

The side of a fifty-three-foot trailer is roughly forty feet of open air at about windshield height. It sits across traffic lanes every time a truck turns or backs.

How many people that kills, depending on who you ask

NHTSA and IIHS are miles apart on this, and the gap is instructive.

NHTSA's position. In a June 2024 Report to Congress the agency put it at 89 fatalities annually among light passenger vehicle occupants in tractor-trailer side underride crashes, within the scope Congress told it to examine. In its 2023 notice it estimated universal side guards would save 17.2 lives and prevent 69 serious injuries a year. Its cost-benefit math came out negative - between negative $1.038 billion and negative $844 million - with annual benefits of $128.5 to $165.9 million against costs of $972.7 million to $1.2 billion.

IIHS's position. In June 2023 IIHS answered that a side guard mandate "could prevent 159-217 passenger vehicle occupant fatalities per year." Roughly ten times NHTSA's number. IIHS faulted the agency for leaving out multi-vehicle crashes and crashes above 40 miles an hour, and for using "speed limits and police-estimated pre-crash speeds rather than actual velocity changes gathered from event data recorders."

IIHS supplied context numbers too. In 2021 there were 488 passenger vehicle occupant fatalities in crashes involving the side of a tractor-trailer. And going back to 2015 data: of 1,542 passenger vehicle occupant deaths in tractor-trailer crashes, 301 involved the side against 292 involving the rear. Read that last one again. The completely unregulated surface killed slightly more people than the regulated one.

And notice how GAO's counting problem feeds this whole dispute. When police reports don't reliably record underride, every estimate built on those reports inherits the hole.

They tested it. It worked.

IIHS ran a side guard called the AngelWing, made by Airflow Deflector Inc. into a trailer and published what happened. At 35 miles an hour with no side protection: "the Malibu ended up lodged under the trailer with part of its roof torn off." IIHS said there "would likely be no survivors in the car." At 40 miles an hour with the guard on: "the side guard bent but didn't allow the car to go underneath the trailer, and the car's airbags and safety belt properly restrained the dummy in the driver seat." IIHS assessed "a low likelihood of injuries in a similar real-world crash."

Faster crash. Survivable. The only variable was a piece of steel bolted to the side of a trailer.

Fifty-five years of asking

The National Transportation Safety Board first recommended side underride protection in 1971, in Safety Recommendation H-71-42. It asked again in 2013 with H-13-13 and H-13-14 on single-unit trucks, and again with H-14-2 and H-14-3 for trailers and truck-tractors. It has separately pushed for better conspicuity treatments on truck sides and rears. Commenting on NHTSA's 2023 notice, NTSB called for "a more comprehensive and systemic approach to address the broader problem of heavy vehicle underride."

Fifty-five years of recommendations and no requirement.

Congress has taken runs at it. The Stop Underrides Act has been introduced in successive sessions, most recently reintroduced in February 2026, which would mandate side guards on new trailers, semitrailers and single-unit trucks. It hasn't passed.

What to do with all that

Two things, if you drive in Mississippi.

  1. Following distance is underride protection. The guard on the back of the trailer ahead of you was engineered to a 35 mile-per-hour standard. At 70 on I-55 you are well outside what it was built for. Space is the only thing keeping you from finding out.
  2. Watch for turning and backing trailers, especially after dark. The side is the unregulated surface. A trailer crossing a rural highway at an unlit intersection is a dark wall at windshield height, and a strip of reflective tape is all that's marking it.

And if it already happened

Underride cases need documentation that routine crash investigation doesn't produce. Whether the rear guard was there, what shape it was in, whether it met the standard that applied, whether it ever got inspected as part of the annual inspection required by 49 C.F.R. § 396.17 — those are answerable questions, but only by somebody who looks at the trailer before it's repaired, sold, or cut up for scrap.

And given that GAO found police reports often don't even record that underride happened, nobody should assume the crash report caught what actually took place.

Sources

This article is provided for general informational purposes only and does not constitute legal advice, nor does it create an attorney-client relationship. Every case turns on its own facts. Statistics cited are drawn from the public sources listed and reflect the data years indicated; figures are updated periodically by the issuing agencies. If you have questions about a specific situation, consult a licensed attorney. Coxwell & Associates, PLLC, 500 North State Street, Jackson, Mississippi 39201. Free background information available upon request.