What It Means
In an underride crash, a car hits a trailer and slides beneath it, so the trailer’s body can strike the car’s passenger compartment. Federal safety standards define a rear impact guard as a device that “limits the distance that the striking vehicle’s front end slides under the rear end” of the trailer (49 CFR 571.223).
Under 49 CFR 393.86, each trailer and semitrailer with a gross vehicle weight rating of 10,000 pounds or more that was manufactured on or after January 26, 1998, must have a rear impact guard that meets Federal Motor Vehicle Safety Standard (FMVSS) No. 223, which covers the guard itself, and FMVSS No. 224, which covers how it is installed. Among other requirements, the bottom of the guard may not be more than 22 inches above the ground. Some vehicles are excepted, including pole trailers, pulpwood trailers, low chassis vehicles, special purpose vehicles, and wheels back vehicles. Older vehicles follow a separate rule with a 30-inch limit.
Side underride guards are a different matter. When we reviewed the current federal regulations in October 2026, we did not find a federal rule requiring side underride guards on trailers.
Why It Matters in a Truck Accident Case
A missing, damaged, or poorly maintained rear guard can turn a rear-end collision into a far more serious crash. Federal rules require motor carriers to “systematically inspect, repair, and maintain” the vehicles they control (49 CFR 396.3). Photos of the trailer, the condition of the guard, and the company’s inspection and maintenance records can help show whether the trailer met these rules, so it is important to act quickly to preserve that evidence.
