The Deadly Flaw in Commercial Trailers: Why Underride Guards Fail in Crashes
When a passenger car rear-ends another passenger car, the bumpers align, crumple zones activate, and airbags deploy, usually allowing the occupants to walk away with minor injuries. But when a passenger car rear-ends a commercial semi-truck trailer, the physics change dramatically. Because the trailer bed is significantly higher than the hood of a car, the car can slide completely underneath the trailer. This is known as an "underride crash."
To prevent this gruesome outcome, federal law requires commercial trailers to be equipped with a rear impact guard—a steel bar hanging below the trailer bed, commonly called a "Mansfield bar" or an underride guard. Its sole purpose is to stop a passenger car from going underneath. Yet, every year, hundreds of these steel guards shear off or crumple on impact, resulting in catastrophic decapitations and fatal crush injuries. Investigating the deadly flaw in commercial trailers and why underride guards fail in crashes is critical for holding negligent trailer manufacturers and trucking companies accountable.
A properly functioning underride guard is designed to absorb the kinetic energy of a passenger car traveling at 35 mph, engaging the car's front crumple zones and allowing the vehicle's safety systems (airbags and seatbelts) to protect the occupants. If the guard fails, the car's windshield and A-pillars take the full force of the steel trailer bed, completely bypassing the car's built-in safety features.
Why Do These Guards Keep Failing?
When an underride crash occurs, trucking defense attorneys immediately blame the driver of the passenger car for "following too closely." However, a plaintiff's attorney will investigate why the safety equipment failed to protect the public. The failures usually fall into three categories of negligence:
Underride guards take a beating. They frequently scrape against loading docks, speed bumps, and steep driveways. This constant stress cracks the welds. Furthermore, exposure to road salt causes severe rust and corrosion at the mounting points. If a trucking company fails to inspect and repair a rusted, cracked guard, the weak steel will instantly snap under the force of a collision.
Many older trailers have underride guards that are only strong in the dead center. If a passenger car strikes the outer 30% of the guard (an "offset crash"), the vertical support beams buckle immediately, allowing the car to slide under the corner of the trailer. This known design flaw has sparked massive lawsuits against trailer manufacturers for failing to reinforce the outer edges of their guards.
For decades, the FMCSA standards for underride guard strength were notoriously weak. While regulations have improved recently, thousands of "grandfathered" trailers from the 1990s and early 2000s are still on the road with completely inadequate, flimsy rear impact guards that offer virtually zero protection at highway speeds.
Holding Multiple Parties Liable
In an underride crash, liability is highly complex. Even if the passenger car driver caused the initial rear-end collision, a specialized attorney can file a "crashworthiness" claim. This argues that the victim's catastrophic injuries were not caused by the initial impact, but by the failure of the trailer's safety equipment. This allows victims to seek massive compensation from both the trucking company (for poor maintenance) and the trailer manufacturer (for defective product design).