A chassis designed for container transport by manufacturer Stoughton is the first of its kind to qualify for the Insurance Institute for Highway Safety (IIHS) Toughguard award for superior underride protection.

A rear underride guard is a metal frame attached to the back of a semitrailer to prevent lower-riding vehicles from sliding underneath the trailer in a rear-end crash. All rear underride guards must meet federal safety standards. However, IIHS says its research and crash tests have shown that many guards can buckle or break off in a crash.

Stoughton’s 53-foot intermodal chassis also meets IIHS’ Toughguard criteria, applicable to models built after April 2025. An intermodal chassis is a special type of trailer that can carry shipping containers directly transferred from ships or railcars.

“We’re excited about the commitment that Stoughton has shown to preventing underride crashes,” said IIHS President David Harkey, in a press release. “Improving the safety of commercial vehicles is a key part of our 30×30 strategy, which targets a 30% reduction in road fatalities by 2030.”

The 30×30 strategy is the IIHS’ goal to reduce traffic fatalities 30% by 2030, which it asks everyone who cares about reducing the “tragic toll” of motor vehicle crashes to unite around.

IIHS testing on semitrailer rear underride guards began in 2012.

During a presentation at the April 2023 Collision Industry Conference (CIC) meeting, IIHS Senior Test Coordinator Sean O’Malley highlighted how far crash testing has come and what challenges lay ahead.

The first eight semitrailer manufacturers were tested with 2010 Malibus at 30%, 50%, and 100% width, or overlap. All manufacturers’ trailers stopped the Malibus at 100%, and all but one, Vanguard, stopped them at 50%. Only one manufacturer, which O’Malley didn’t name, stopped the Malibus at 30%. A year later, Vanguard contacted IIHS and asked that the test be redone. Both passed the 30% and 50% tests.

Within two years, the other seven manufacturers wanted their new designs, either standard or optional, tested. By 2019, they all passed IIHS’ rear underride guard tests. O’Malley estimated that well over 90% of semi-trucks on U.S. roads are equipped with underride guards that have passed all three of IIHS’ tests.

Underride guards that meet the Toughguard criteria are substantially more likely to withstand an impact, reducing the severity of the crash, according to IIHS.

IIHS crashes a midsize car into the back of a parked trailer at 35 mph in three configurations, hitting the trailer with its full width, a 50% overlap, and a 30% overlap. To earn the IIHS award, the guard must prevent underride in all three configurations. The 30% overlap configuration, which IIHS notes was left out of the new federal requirements, is the most challenging because only the corner of the underride guard must absorb all the force of the impact.

Initially, the tests were conducted in-house. Now, IIHS allows trailer manufacturers to submit data and footage from tests conducted at their facilities or by contractors for IIHS experts to review. The tests of Stoughton’s intermodal chassis were conducted by Calspan.

“Until now, only dry van, refrigerated, and flatbed trailers have qualified,” the release states. “But with the growing importance of shipping containers in global trade, more and more freight is being transported using intermodal chassis.

“Chassis-type trailers present a unique challenge when it comes to underride protection. The frame of a dry van, refrigerated, or flatbed trailer extends across its entire wheelbase, supporting the underride guard for its full width. In contrast, an intermodal chassis is a ladderlike structure that lies between the trailer’s wheels to support the removable container. For that reason, the underride guard required a completely new design. Instead of a vertical support attached to the trailer deck, the chassis guard features long, diagonal supports running from the guard’s outboard ends to the chassis rails.”

The National Highway Traffic Safety Administration (NHTSA) updated federal regulations governing rear underride protection on large trucks in June 2022. However, IIHS claims the new rule remains far less stringent than the Toughguard requirements and isn’t expected to push manufacturers to improve.

“A major weakness of the federal regulation is that in the required test, the underride guard is bolted to a universal testing rig instead of an actual trailer,” O’Malley said in the release. “When we were developing the Toughguard program, we found that many underride guards that survived testing attached to NHTSA’s rig broke off when attached to the trailer they were built to be used on, either because the attachment points on the trailer failed or the bolts did.”

In contrast, IIHS said it evaluates underride guards on the trailers they’re designed for.

Stoughton was also among the earliest trailer manufacturers to earn a Toughguard award for its dry vans and refrigerated trailers in 2017. To date, nine North American trailer manufacturers, including the eight largest, have earned Toughguard awards.

Images

Featured image: Calspan crash test photo provided by IIHS