An underride accident occurs when a passenger vehicle slides beneath a semi-trailer, so that the trailer’s steel frame intrudes directly into the car’s passenger compartment. The car’s crumple zones, airbags, and roof structure never get the chance to do their job, because the collision happens above them. On Illinois interstates like I-80 and I-88, and on the Dan Ryan, these are among the deadliest crashes that occur — and liability often extends well beyond the truck driver to the motor carrier, the trailer’s owner, and even its manufacturer.
This article explains how underride crashes happen, what federal law requires, and who can be held accountable.
Underride crashes come in two main forms. A rear underride crash happens when a car strikes the back of a trailer and slides beneath it, often because the truck was stopped, moving slowly, or parked on the shoulder at night without proper warnings. A side underride crash happens when a trailer crosses or blocks a roadway, frequently while turning or making a U-turn, and an oncoming car passes under the trailer between its axles.
In both scenarios, the geometry is the problem. The floor of a typical semi-trailer sits roughly at the height of a car’s windshield. When the vehicles meet, the trailer bed overrides the car’s hood and enters the cabin at head level.
Modern cars are engineered to sacrifice themselves to save their occupants. The front end crumples to absorb energy, sensors trigger airbags, and a reinforced safety cage protects the people inside. Every one of those systems assumes the car will hit something at bumper height.
An underride collision defeats all of it. The trailer passes over the bumper and the engine block, so the crash forces are absorbed by the windshield pillars and the roof instead. Airbags may never deploy because the bumper sensors are never struck. The result is that occupants suffer devastating head, neck, and chest injuries even in collisions at moderate speeds that would otherwise have been survivable. Survivors of these crashes often live with traumatic brain injuries, facial trauma, and spinal damage that alter every part of their lives, and many underride collisions are fatal. For those who survive, recovery typically begins at a Level I trauma center such as Northwestern Memorial Hospital in Chicago or Advocate Christ Medical Center in Oak Lawn, followed by long-term rehabilitation at a facility like the Shirley Ryan AbilityLab in Chicago — and a Life Care Plan projecting those decades of future needs becomes central to the damages case.
Federal regulators have required rear guards, sometimes called underride guards or Mansfield bars, for decades. Under 49 CFR 393.86, most trailers and semitrailers with a gross vehicle weight rating of 10,000 pounds or more that were manufactured on or after January 26, 1998 must be equipped with a rear impact guard that meets Federal Motor Vehicle Safety Standard No. 223, and the vehicle itself must meet Standard No. 224. The regulation sets specific geometry: the bottom edge of the guard generally may not sit more than 22 inches above the ground, the guard must extend to within 4 inches of each side of the trailer, and it must sit within 12 inches of the trailer’s rear extremity. Older vehicles are covered by a separate requirement when the rear of the body sits more than 30 inches off the ground.
The standards have also been strengthened. On June 30, 2022, NHTSA announced a final rule upgrading FMVSS 223 and 224 so that rear impact guards on new trailers provide improved strength and energy absorption, part of a mandate from Congress in the Bipartisan Infrastructure Law.
A guard that is missing, corroded, bent from a previous impact, or improperly repaired may not comply with these rules, and that noncompliance can become central evidence in an injury case.
Side underride protection is a different story. Federal law requires rear guards, but there is currently no federal requirement that trailers carry side underride guards. In its 2022 announcement, NHTSA said it would establish an advisory committee on underride protection, publish an advance notice of proposed rulemaking on side underride guards, and research their effectiveness, feasibility, and cost.
That means the debate is live but unresolved. For crash victims, the absence of a side guard mandate does not end the inquiry. A trucker who blocked a dark highway while making an illegal or careless turn, or a carrier that routed a driver into a maneuver requiring the trailer to occupy oncoming lanes, can still be fully liable for a side underride crash under ordinary negligence principles.
One of the defining features of underride litigation is the number of potentially responsible parties. Depending on the facts, a claim may involve:
Untangling these relationships takes real investigation, because ownership, leasing, and maintenance duties in trucking are deliberately layered. Our overview of who is liable in a truck accident explains how each of these parties gets identified and pursued.
The list of defendants also shapes where the case is filed. Under Illinois’ venue statute, 735 ILCS 5/2-101, suit generally may be brought in the county where any defendant joined in good faith resides or in the county where the crash — or some part of the transaction — occurred. An underride collision on I-80 or I-88 may belong in Will County or DuPage County, while a crash on the Dan Ryan typically means the Circuit Court of Cook County Law Division at the Daley Center. Venue affects the jury pool and the case’s timeline, and it is one of the first strategic decisions experienced local counsel makes.
Underride cases are built on physical and electronic proof, and the most important evidence is the trailer itself. The guard’s condition, its mounting hardware, prior repair welds, and measurements of its height and width against the federal specifications can establish a violation of 49 CFR 393.86. Photographs must be taken before the trailer is repaired or scrapped, which is why preservation letters need to go out immediately.
Beyond the guard, a strong case typically draws on the truck’s electronic control module, dash camera footage, the carrier’s inspection and maintenance records, the driver’s logs, lighting and reflective tape condition, and accident reconstruction analysis of speeds and sight lines. Our guide to truck accident evidence covers how this material is located and preserved before it disappears.
Time is the enemy. Carriers know what a bent guard proves, and trailers get repaired fast. Getting counsel involved in the first days after a crash can make the difference between a documented violation and a repainted trailer.
An underride accident is a crash in which a passenger vehicle slides beneath a semi-trailer, either from the rear or the side, so the trailer intrudes into the passenger compartment. These crashes bypass the car’s bumper, crumple zones, and airbag sensors, which is why they cause such severe head and neck injuries.
Federal regulation 49 CFR 393.86 requires rear impact guards meeting FMVSS 223 and 224 on most trailers manufactured since January 26, 1998, and NHTSA strengthened the rear guard standard in 2022. Side underride guards are not currently required by federal law, though NHTSA has studied them and sought public input on a potential requirement.
Depending on the facts, claims may be brought against the truck driver, the trucking company, the trailer’s owner, the trailer or guard manufacturer, and maintenance contractors. An investigation into the guard’s condition and the companies responsible for it usually determines the full list of defendants.
An underride accident leaves families facing the worst injuries the law recognizes, and the evidence that proves responsibility can vanish within weeks. The Illinois truck accident lawyers at Collins Law Group, P.C. move immediately to preserve the trailer, the guard, and the carrier’s records, and we work with reconstruction and engineering experts to hold every responsible company accountable. Consultations are always free, and we are paid only if we recover for you. Contact us today to protect your family’s claim.
John D. Risvold is an equity partner at Collins Law Group, P.C. in Naperville, Illinois. He represents individuals and families in catastrophic personal injury and wrongful death cases, focusing on commercial trucking crashes, rideshare and autonomous vehicle litigation, medical malpractice and birth injury, and product defect claims. He has tried cases to verdict in Illinois courts, recovered more than $50 million for clients over thirteen years of practice, and has been named to Best Lawyers in America for Personal Injury Litigation and Illinois Super Lawyers.
This article is for general information only and is not legal advice. Reading it does not create an attorney-client relationship. Every case is different; if you have been injured, speak with a lawyer about your specific situation.
