New trailer type gets strong underride guard

Stoughton extends IIHS-award-winning underride protection to container shipping

/EIN News/ -- ARLINGTON, Va., June 12, 2025 (GLOBE NEWSWIRE) -- A Stoughton chassis designed for container transport is the first of its kind to qualify for the Insurance Institute for Highway Safety’s TOUGHGUARD award for superior underride protection. 

Wisconsin-based Stoughton, a leading manufacturer of semitrailers, previously earned the award for its dry vans and refrigerated vans. Now the company’s 53-foot intermodal chassis also meets the TOUGHGUARD criteria. The award applies 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,” IIHS President David Harkey said. “Improving the safety of commercial vehicles is a key part of our 30x30 strategy, which targets a 30% reduction in road fatalities by 2030.” 

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

Underride guards that meet the TOUGHGUARD criteria are substantially more likely to withstand an impact, reducing the severity of the crash. Until now, only dry van, refrigerated and flatbed trailers have qualified. 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 ladder-like 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, the new rule remains far less stringent than the TOUGHGUARD requirements and is not 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,” IIHS Senior Test Coordinator Sean O’Malley said.  

“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 evaluates underride guards on the trailers they are designed for.  

In the IIHS test, a midsize car crashes into the back of the 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 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, these tests were conducted in-house. Now IIHS allows trailer manufacturers to submit data and footage from tests conducted at their own facilities or by contractors for IIHS experts to review. The tests of Stoughton’s intermodal chassis were conducted by Calspan. 

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. 

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For more information, go to iihs.org 

The Insurance Institute for Highway Safety (IIHS) is an independent, nonprofit scientific and educational organization dedicated to reducing deaths, injuries and property damage from motor vehicle crashes through research and evaluation and through education of consumers, policymakers and safety professionals. IIHS is wholly supported by auto insurers. 

Joe Young
                    Insurance Institute for Highway Safety
                    504-641-0491
                    jyoung@iihs.org