Rear underride guard mandate may extend to more trucks under NHTSA proposal

November 10, 2015

The federal government has outlined a possible plan to close a deadly loophole in truck safety rules by requiring rear underride guards on single-unit trucks.

Until now, the guards — steel bars that hang from the back of trucks to prevent a passenger vehicle from moving underneath in a crash — have been mandated only on semitrailers and certain single-unit trucks involved in interstate commerce. Most single-unit trucks aren't subject to the requirement.

Single-unit trucks make up nearly three-quarters of the registered heavy vehicle fleet. They include many types of trucks designed for specific tasks, including dump trucks, garbage haulers, local delivery trucks and concrete mixers.

Single-unit truck
Single-unit trucks like the ones shown here are exempt from National Highway Traffic Safety Administration requirements for rear underride guards. The agency is considering closing that loophole. Underride guards prevent smaller vehicles from going underneath a truck in a crash.

The National Highway Traffic Safety Administration (NHTSA) estimates that underride guards on single-unit trucks would save five lives per year and prevent 30 injuries. Institute researchers say that estimate is low.

"Requiring rear underride guards is an important step that would reduce fatalities in large truck crashes," says Matthew Brumbelow, an IIHS senior research engineer. "We hope NHTSA will reconsider some of the assumptions it used to calculate how many lives could be saved before deciding whether or not to proceed with this regulation."

Specifically, NHTSA uses an estimate of the proportion of fatal crashes that involve severe underride that was derived from interviews taken long after the crash and thus may not be accurate, Brumbelow says. Also, in looking at how many of those fatalities could have been prevented by guards, the agency doesn't take into account crashes with impact speeds over 35 mph. IIHS crash tests at 35 mph suggest the guards would likely hold up at higher speeds.

In an official comment to NHTSA, IIHS took issue with the agency's estimate that a requirement for single-unit trucks would cost up to nearly $2,000 per truck. This calculation is based on weight estimates of underride guards that are much higher than actual measurements the Institute has taken.

The plan, which would require underride guards on single-unit trucks with a gross vehicle weight rating of 10,000 pounds or more, was laid out in an advance notice of proposed rulemaking issued in July. NHTSA also is proposing to require the same reflective tape currently required on semitrailers, an idea IIHS supports. NHTSA estimates that requirement could save as many as 14 lives per year by making trucks easier to see and thereby preventing crashes.

This notice is the first of two steps the agency said it would take when it granted a petition to consider more stringent underride rules last year.

Next, NHTSA is expected to propose an upgrade to the existing requirements for all truck underride guards, including those on semitrailers. IIHS research has shown that meeting the current standard isn't enough to prevent underride in many cases, particularly in offset crashes.

In the advance notice on single-unit trucks, NHTSA estimated the effect of guards that meet Canada's standard, which is stronger than the current U.S. standard for the guards required on semitrailers. While the Canadian standard is an improvement over the U.S. standard, IIHS research has shown that it is possible to build guards that do a better job than those meeting either standard when it comes to preventing underride in certain offset crash scenarios (see "Underride guards can be lifesavers, but most could be improved," March 14, 2013).

"We hope that NHTSA will consider a more comprehensive solution for both single-unit trucks and semitrailers than simply adopting the Canadian standard," Brumbelow says.

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