In 2024, passenger vehicle occupants accounted for 96% of vehicle-occupant deaths in two-vehicle crashes involving a passenger vehicle and a large truck, according to the Insurance Institute for Highway Safety. Large trucks can weigh many times as much as passenger vehicles and sit substantially higher off the road, creating a fundamental mismatch in crash geometry.

What Is an Underride or Override Truck Crash?

Underride occurs when part of a passenger vehicle travels beneath a truck or trailer during a collision. It can happen when a car strikes the rear or side of a trailer. Instead of the passenger vehicle’s bumper, frame rails, crumple zones, airbags, and restraints managing the crash as intended, the higher truck structure can intrude into the windshield, roof, or occupant compartment.

Override describes the opposite interaction: the large truck travels over part of the smaller vehicle. A truck’s front structure may pass above the passenger vehicle’s primary energy-absorbing structure, allowing severe intrusion into the occupant compartment.

Both involve a concept engineers call crash compatibility. The safety structures of the two vehicles need to engage in a way that allows crash energy to be managed. When their height, stiffness, width, or structural geometry is badly mismatched, the passenger vehicle’s safety systems may have far less opportunity to protect its occupants.

That is why an underride or override collision should not automatically be analyzed as an ordinary commercial vehicle collision.

Rear Underride Guards Are Designed to Keep Cars from Going Under Trailers

Rear impact guards are structural devices mounted low on the back of many trailers and semitrailers. Their purpose is straightforward: engage the front of a passenger vehicle and limit how far it can travel underneath the trailer.

Federal Motor Vehicle Safety Standards 223 and 224 regulate rear impact guards and rear impact protection for many trailers and semitrailers weighing more than 10,000 pounds, subject to defined exemptions. NHTSA strengthened those requirements in 2022. The updated standard addresses a passenger vehicle striking the rear of a trailer at 35 mph in full-width and 50% overlap configurations.

But real-world crashes do not always happen squarely in the center of a trailer.

A passenger car may strike only the outside corner. IIHS testing specifically evaluates a more demanding 30% overlap configuration because protection near the outer edges of a trailer presents a different engineering challenge. Current IIHS criteria also recognize trailers that provide protection in that narrow-overlap condition.

That distinction can become critical in litigation. Investigators may need to determine:

• Whether the guard engaged the passenger vehicle at all
• Whether the horizontal member bent or separated
• Whether vertical supports or attachment points failed
• Whether the trailer chassis deformed around the guard
• Whether the guard provided adequate protection near its outer edges
• Whether corrosion, prior damage, modification, or poor repairs weakened the system
• Whether the guard was mounted at the proper height and distance from the rear of the trailer

The fact that a guard was physically present does not answer whether it functioned safely in the actual collision.

Side Underride and Front Override Expose Additional Design Questions

Rear guards address only part of the problem.

As of 2026, there is no federal requirement for front or side underride guards in the United States. NHTSA has studied potential side-underride requirements, and IIHS crash testing has demonstrated that structural side guards can prevent a passenger vehicle from traveling underneath a trailer in certain crash configurations.

A side-underride crash can occur when a tractor-trailer crosses, turns, jackknifes, changes lanes, or blocks part of a roadway and a passenger vehicle enters the open space beneath the trailer.

Front override presents another geometry problem. The front bumper, frame, and other structures on a large commercial truck may sit substantially higher than the crash structures on a smaller passenger vehicle. Investigators may need to examine whether the vehicles interacted as their manufacturers anticipated and whether alternative designs could have reduced intrusion into the occupant compartment.

These questions can move a case beyond ordinary driver negligence and into the realm of product liability and vehicle design.

Conspicuity Can Matter Before the Impact Ever Happens

Some underride crashes also involve a visibility problem.

Federal safety standards require conspicuity systems on many large trailers and truck tractors. Depending on the vehicle, these systems include red-and-white retroreflective material and reflectors positioned along the sides and rear to help approaching motorists recognize the vehicle’s presence, width, and orientation in low-light conditions.

After a nighttime underride crash, investigators should document more than whether reflective tape existed somewhere on the trailer.

Relevant questions include:

• Was required reflective material present?
• Was it positioned where federal requirements called for it?
• Was it damaged, dirty, faded, missing, or obscured?
• Were rear, side-marker, hazard, or clearance lamps operating?
• Did cargo or equipment block required conspicuity treatment?
• Had the carrier identified visibility problems during previous inspections?
• Did a repair, modification, or body installation change the trailer’s visibility profile?

Conspicuity evidence can be especially important when a trailer was stopped, backing up, turning, crossing traffic, or positioned partially across a roadway after dark.

A Guard Failure Can Create Both Product Liability and Trucking Claims

One of the most important questions after a catastrophic underride crash is who controlled the safety system that failed.

Potential defendants may extend well beyond the truck driver.

Trailer manufacturer. A claim may examine the original design of the trailer, rear guard, chassis, attachment points, side structure, and the interaction among those components.

Underride guard or component manufacturer. If another company designed or supplied the guard, supports, fasteners, or related components, its design and manufacturing decisions may require separate investigation.

Truck or tractor manufacturer. Front override cases may require engineering analysis of bumper height, structural geometry, crash compatibility, and other aspects of the truck’s front-end design.

Motor carrier or trailer owner. The company operating or owning the equipment may be responsible for inspection, repair, maintenance, and continued operation of a damaged guard or deficient conspicuity system. Federal periodic inspection standards specifically address missing rear guards, insecure attachments, cracked welds, structural damage, and dimensional problems.

Maintenance or repair company. Improper welding, replacement components, unauthorized modifications, or inadequate repairs may weaken an otherwise functional safety system.

Body builder or equipment upfitter. Companies that modify trailers or commercial vehicles may alter structural components, guard placement, lamps, reflective material, or other safety features.

Driver and motor carrier. Driver negligence and corporate trucking safety failures can still remain central. Unsafe lane changes, backing, parking, lighting failures, inadequate inspections, or knowingly operating damaged equipment may exist alongside a product-defect claim.

In some cases, investigators may also examine the passenger vehicle itself. A separate auto defect or crashworthiness issue involving restraints, airbags, seats, roof structure, or another occupant-protection system could have increased the severity of the injuries.

Responsibility depends on the evidence and applicable state and federal law. Compliance with a federal minimum standard is an important part of that analysis, but it does not necessarily answer every state-law design-defect or negligence question.

The Truck and Trailer Are Critical Evidence

Underride and override cases are heavily dependent on physical evidence. A trailer that is repaired, sold, returned to service, or scrapped can carry crucial evidence with it.

A serious investigation should consider preserving and documenting:

• The tractor, trailer, and passenger vehicle
• Rear guard dimensions, deformation, welds, bolts, supports, and attachment points
• Trailer chassis deformation
• Conspicuity tape, reflectors, lamps, and electrical systems
• Vehicle event data recorder information
• Tractor electronic control module and telematics data
• Dashcam or fleet-camera footage
• Maintenance and periodic inspection records
• Prior guard repairs or collision damage
• Trailer specifications, build records, and component information
• Scene photographs, surveillance video, roadway lighting, and visibility conditions
• Measurements or 3D scans showing the relative geometry of the vehicles

Engineers may then reconstruct how the vehicles interacted and determine whether the guard, trailer, tractor, or passenger vehicle performed as designed.

Underride Cases Require More Than a Driver-Fault Investigation

A truck driver may have caused the initial collision. That does not mean the investigation should stop with the driver.

A catastrophic underride or override case can involve two different questions:

Why did the vehicles collide?

And separately:

Why did that collision produce such severe occupant-compartment intrusion?

The first question may identify driver or motor-carrier negligence. The second may identify defective guarding, inadequate crash compatibility, insufficient conspicuity, poor maintenance, or another product design issue.

Answering both questions is essential when determining whether multiple companies contributed to a catastrophic injury or death.

When a Truck Crash Becomes a Product Liability Investigation

Underride and override crashes sit at the intersection of trucking negligence, engineering, crash reconstruction, and product liability. A complete investigation should evaluate the conduct that caused the collision and the safety systems that were supposed to keep that collision survivable.

If you or a family member suffered catastrophic injuries or lost a loved one in an underride or override truck crash, contact McEldrew Purtell for a free consultation. Our attorneys can investigate the truck and trailer, guard and vehicle design, conspicuity, maintenance history, crash geometry, and the companies responsible for each part of the vehicle and its operation.