Underride Truck Accidents in Illinois

Last Updated: October 27, 2026

Underride accidents occur when cars slide under truck trailers, often causing fatal injuries. 49 CFR 571.224 requires a rear impact guard on the trailers and semitrailers it covers. Its purpose is to reduce deaths and serious injuries when a light-duty vehicle hits the rear of a covered trailer. That standard does not require a side guard, and a missing guard does not by itself decide liability.

A sedan approaches a tractor-trailer that has slowed or stopped on the highway ahead. The car slides beneath the rear or side of the trailer, and the trailer’s edge strikes at windshield height, shearing off the roof of the passenger compartment. This is an underride crash, and it is among the most lethal types of collisions on American roads. Many of these deaths are preventable with equipment that has existed for decades.

How Underride Accidents Happen

Underride crashes occur when a smaller vehicle passes beneath the body of a large truck or trailer. There are two primary types. A rear underride happens when a vehicle strikes the back of a trailer, typically because the truck stopped or slowed suddenly, was poorly lit, or was parked without adequate warning. A side underride occurs when a vehicle collides with the side of a trailer during a turn or at an intersection, passing beneath the gap between the trailer floor and the road surface.

The physics are devastating. Standard passenger vehicle safety systems, including crumple zones, airbags, and seatbelts, are designed to absorb frontal or angular impacts. They are not designed for a scenario where the vehicle’s occupant compartment passes under a rigid steel structure. The result is often decapitation, catastrophic head trauma, or fatal crush injuries to the upper body.

Federal Rear Guard Requirements and Their Limits

49 CFR 571.224 sets requirements for installing a rear impact guard. It applies to the trailers and semitrailers covered by the standard. The application subsection excludes pole trailers, pulpwood trailers, low chassis vehicles, road construction controlled horizontal discharge trailers, special purpose vehicles, wheels back vehicles, and temporary living quarters. 49 CFR 571.223 tests the guard’s strength and energy absorption, including a 50,000 newton point load and a distributed load of at least 350,000 newtons. Those two sections address a rear impact guard.

The problem is that many real-world crashes happen at speeds well above 30 mph, and the guards often fail. The Insurance Institute for Highway Safety (IIHS) has tested rear guards and found that many do not withstand moderate-speed offset impacts. Stronger guards, such as those meeting the IIHS TOUGHGUARD standard, perform far better but are not federally mandated. There is currently no federal requirement for side underride guards at all, despite years of advocacy and proposed legislation.

Liability in an Underride Crash

An underride case can involve several theories of liability. Under 49 CFR 392.22, a driver who stops on the traveled portion or the shoulder for a reason other than a necessary traffic stop must immediately activate the hazard flashers. As soon as possible, and within 10 minutes, the driver must place the required warning devices: one about 10 feet toward approaching traffic on the traffic side, and one about 100 feet in each direction in the occupied lane or shoulder. The section states different placements for a hill, a curve, or a divided highway. Paragraph (a) is the immediate flasher duty, and that duty remains. Paragraph (b)(2)(iii) is limited to placement of the warning devices. Placement is not required within the business or residential district of a municipality, except when lighted lamps are required and the street or highway lighting is insufficient to make the vehicle clearly discernable at 500 feet. A turn that fails to yield is a separate negligence question. The motor carrier may be liable for failing to equip trailers with adequate guards, for using trailers with damaged or non-compliant guards, or for inadequate lighting and reflective markings.

In some cases, a product liability claim against the trailer manufacturer or guard manufacturer is appropriate, particularly if the rear guard failed at a speed within its design parameters. Illinois product liability law allows claims based on strict liability, negligence, or breach of warranty. As discussed in our overview of Peoria truck accident claims, building a strong case means identifying every party whose negligence contributed to the crash.

Damages in Underride Cases

Because underride crashes so often result in death or catastrophic injury, the damages tend to be substantial. In a wrongful death case, 740 ILCS 180/2 lets the personal representative bring the action for the exclusive benefit of the surviving spouse and next of kin. The jury may award fair and just compensation for the pecuniary injuries resulting from the death, including grief, sorrow, and mental suffering, and punitive damages when applicable. Punitive damages are not available in a healing-art or legal-malpractice action, or against the State, a unit of local government, or their employees in an official capacity. 755 ILCS 5/27-6 provides that an action to recover damages for an injury to the person survives, except an action for slander or libel. In cases involving survivors, damages may include lifelong medical care, permanent disability, traumatic brain injury treatment, and the profound loss of quality of life that follows a catastrophic head or spinal injury.

Investigating an Underride Crash

Evidence in these cases is highly technical. An accident reconstruction expert can analyze the point of impact, the speed of both vehicles, and the performance of the rear or side guard. The truck’s ECM data will show speed, braking, and whether the driver was decelerating before the collision. Photographs of the trailer guard, the vehicle’s roof line, and the overall crash scene are essential. Maintenance records should show whether the guard was properly attached and in compliance with federal standards. If the trailer had damaged or missing reflective tape or inoperative marker lights, those failures may have contributed to the crash by making the trailer invisible to approaching drivers.

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Frequently Asked Questions

Are side underride guards required by law?

49 CFR 571.223 and 571.224 require a rear impact guard on the trailers they cover. They do not require a side underride guard. Several bills have been introduced in Congress to mandate side underride guards, but none have been enacted as of early 2026. Some carriers voluntarily install side guards, and several other countries require them. The absence of a legal mandate does not prevent you from arguing that a reasonable carrier should have installed them, particularly when the technology is proven and available.

Can I file a lawsuit if a family member died in an underride crash?

Yes. Under the Illinois Wrongful Death Act, a personal representative of the deceased person’s estate can file a lawsuit on behalf of the surviving spouse and next of kin. The claim may be brought against the truck driver, the motor carrier, and potentially the trailer or guard manufacturer. Section 2(d) generally requires the action to be commenced within 2 years after the death. Subsection (e) allows 5 years after the death, or one year after the criminal case ends, when the death results from violent intentional conduct and the claim is against the person charged with one of the listed crimes. That longer period does not extend the time against any other person. A person under 18 who is entitled to recover may bring the action within 2 years after turning 18.

What if the truck was parked on the side of the road?

49 CFR 392.22(a) requires the hazard flashers immediately when a commercial vehicle stops on the traveled portion or the shoulder for a reason other than a necessary traffic stop. Paragraph (b) requires the warning devices as soon as possible, and within 10 minutes: one about 10 feet toward approaching traffic on the traffic side, and one about 100 feet in each direction. A hill, a curve, or a divided highway has a different placement. Paragraph (b)(2)(iii) applies only to placement of those warning devices. Placement is not required within the business or residential district of a municipality, except when lighted lamps are required and the lighting is insufficient to make the vehicle clearly discernable at 500 feet. The immediate flasher duty remains. A failure to follow that rule is evidence of negligence. It does not by itself decide the case. Parking in a travel lane or on the shoulder without proper warning is a well-recognized basis for negligence claims.

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Underride Truck Accidents in Illinois: A Deadly and Preventable Crash