Underride Crashes: What the Deadly I-5 Sun Valley Big Rig Collision Shows About Truck Safety

A semi-trailer sits high off the road. When a smaller vehicle hits the back of it, the trailer bed can line up with the windshield instead of the bumper, and the smaller vehicle can slide underneath. That is an underride crash, and it is one of the most dangerous collisions on any freeway. The rear impact guard, the steel bar hanging below the back of most trailers, exists to stop it.

In short: federal rules require most large trailers to carry a rear impact guard that meets federal strength and design standards, and those standards were strengthened in 2022. When an underride crash happens, the driver of either vehicle, the trucking company, a maintenance shop, or a trailer or guard manufacturer may be part of the legal picture, depending on the evidence. Families who lose someone generally have two years to file a wrongful death lawsuit in California.

If you or someone you love was hurt in a truck crash anywhere in California, Win Attorneys handles truck accidents and wrongful death and catastrophic injury claims statewide. Seek medical care first, even if you feel fine.

Talk to us at (562) 296-5380 or reach out through our contact page for a free case review. Office: 17291 Irvine Blvd., Suite 210, Tustin, CA 92780.

What Happened on the 5 Freeway in Sun Valley

On Wednesday, October 14, 2026, a fatal crash closed the northbound 5 Freeway in Sun Valley. ABC7 reported, citing the California Highway Patrol, that the crash was reported around 11 a.m. near Sheldon Street, and that a white truck was partially wedged under the back of a big rig. ABC7 later corrected its report to say the crash happened in Sun Valley, not Sylmar.

The Los Angeles Fire Department’s incident alert described a two-vehicle collision reportedly involving one truck and one semi-truck. LAFD reported that one adult male died at the scene and another adult male with minor injuries was taken to a hospital. KTLA reported that firefighters worked to free the driver of the white truck and that all northbound lanes were shut down. KTLA said it appeared the truck had struck the back of the big rig.

The person who died had not been publicly identified in the reports we reviewed, and no official finding of cause had been released as of October 15. LAFD referred questions about the investigation to the CHP. We are not assigning fault to anyone, and nothing in the reports describes the condition of the trailer’s rear guard. Our thoughts are with the family of the man who died and with everyone affected.

What the crash does show is why underride protection matters, and what questions investigators and families usually ask afterward.

What Makes Underride Crashes So Dangerous

Passenger cars and pickups are built to absorb a crash through their bumpers, crumple zones, and frame. Those safety systems only work if they make contact. When a vehicle goes under a trailer, the trailer’s rear edge can bypass the hood and strike the windshield pillars and the cabin itself. Engineers call this passenger compartment intrusion. Airbags and seat belts cannot do their job well when the structure around the occupant is crushed.

A rear impact guard is meant to catch the front of the striking vehicle low enough that its own crash structure engages. A guard that is too high, too weak, too narrow, bent, rusted, or missing can let a vehicle slide under.

The Federal Rules on Rear Impact Guards

49 CFR 393.86: guards on trailers in service

The Federal Motor Carrier Safety Regulations govern trucks operating in interstate commerce, and California applies many of the same rules to intrastate carriers. Under 49 CFR 393.86(a)(1), each trailer and semitrailer with a gross vehicle weight rating of 10,000 pounds or more, manufactured on or after January 26, 1998, must be equipped with a rear impact guard that meets Federal Motor Vehicle Safety Standard No. 223 in effect when the trailer was built. Once installed, the trailer must at a minimum meet FMVSS No. 224.

The same section sets dimensional limits. The bottom of the guard’s horizontal member generally may not be more than 22 inches above the ground, the guard must extend to within 4 inches of each side of the trailer, and the guard must sit within 12 inches of the rear of the trailer. There are listed exceptions, including pole trailers, pulpwood trailers, low chassis vehicles, special purpose vehicles, wheels back vehicles, certain road construction trailers, and trailers towed in driveaway towaway operations.

Because 393.86 applies to vehicles in operation, a damaged or missing guard can be a maintenance and inspection question, not just a manufacturing question.

FMVSS 223 and 224: how guards are built and installed

FMVSS No. 223 sets the strength and energy absorption requirements for the guard itself. FMVSS No. 224 requires covered trailers to have a guard that meets FMVSS No. 223 and governs how the guard is mounted on the trailer. Together they are the manufacturing side of underride protection.

The 2022 upgrade

On July 15, 2022, the National Highway Traffic Safety Administration published a final rule upgrading FMVSS Nos. 223 and 224, responding to a mandate in the 2021 Bipartisan Infrastructure Law. According to the Federal Register notice, the rule:

Requires rear impact guards to prevent passenger compartment intrusion in 35 mph (56 km per hour) crashes by compact and subcompact passenger cars into the rear of a trailer.
Covers both full width center impacts and crashes where 50 percent of the car’s width overlaps the trailer.
Largely harmonizes the U.S. standard with Canada’s rear impact guard standard.

The rule took effect January 11, 2023, with a compliance date of July 15, 2024, and early compliance was optional. It applies to newly manufactured trailers and semitrailers, so older trailers on the road may have been built to the earlier standard. NHTSA also considered a requirement for crashes where only 30 percent of the car overlaps the trailer and decided, based on the data then available, not to adopt it.

Who May Be Responsible in an Underride Crash?

Every crash is different, and a rear underride crash is not proof that anyone in particular was at fault. Depending on what the investigation shows, the parties a claim might involve include:

The driver of the striking vehicle, if speed, distraction, or following too closely played a part. Drivers in a rear crash are often presumed at fault by insurers, but that is not the end of the analysis.
The truck driver, if the big rig was stopped or slowed in an unsafe place, lacked working lights or reflectors, or made an unsafe maneuver.
The motor carrier, through its driver under the rules on employer responsibility, and directly if its inspection, maintenance, hiring, or training practices fell short.
A maintenance or repair provider, if a guard was damaged, improperly repaired, or removed.
The trailer or guard manufacturer, if a design or manufacturing defect made the guard weaker than it should have been.

Under California Civil Code section 1714, everyone is responsible for harm caused by a lack of ordinary care. Product liability claims follow their own rules. Comparative fault can reduce, but does not necessarily bar, recovery when more than one party contributed.

Evidence That Matters After an Underride Crash

Truck crash evidence disappears quickly. Trailers are repaired, returned to service, or sold, and electronic data can be overwritten. Important evidence often includes:

The trailer and its rear guard, including measurements, photographs, and the manufacturer’s certification label.
Maintenance and inspection records for the trailer and guard.
Electronic data from the tractor and from the striking vehicle, such as speed and braking information.
Hours of service and logging records for the truck driver.
Dashcam, traffic camera, and nearby business video, which may be overwritten in days.
The CHP collision report and any reconstruction findings.
Witness names and statements taken while memories are fresh.

A preservation letter to the carrier early on can help keep key evidence from being lost.

Wrongful Death Claims and Deadlines

When an underride crash takes a life, California law allows certain family members to bring a wrongful death claim. Code of Civil Procedure section 377.60 lists who may sue, starting with the surviving spouse or domestic partner, children, and those entitled to the person’s property by intestate succession, and in some cases others who were financially dependent on the person.

The general deadline for a personal injury or wrongful death lawsuit in California is two years under Code of Civil Procedure section 335.1. If a public entity may share responsibility, for example through a road condition or a public vehicle, a written government claim generally must be presented within six months. Our government claims page explains that process.

For more on how big rig crashes unfold on busy Southern California freeways, see our guide to freeway work zone truck crashes and our motor vehicle accidents page.

Talk With Win Attorneys

Win Attorneys helps families and injured people across Los Angeles, Orange County, and the rest of California from our Tustin office. Underride cases often turn on technical evidence about the trailer and its guard, and acting early helps preserve it. Our office is fluent in Spanish and Vietnamese; say so when you call.

Talk to us at (562) 296-5380, write through our contact page, or visit 17291 Irvine Blvd., Suite 210, Tustin, CA 92780. The case review is free.

Underride Crash FAQs

What is an underride crash?

An underride crash happens when a smaller vehicle slides under a larger one, usually the rear or side of a semi-trailer. The trailer can strike the windshield and cabin instead of the bumper, so the smaller vehicle’s safety features may not work as designed.

Are trucks required to have rear underride guards?

Most are. Under 49 CFR 393.86, trailers and semitrailers with a gross vehicle weight rating of 10,000 pounds or more built on or after January 26, 1998 must have a rear impact guard meeting FMVSS No. 223, with listed exceptions such as pole trailers and special purpose vehicles.

What changed in the 2022 underride guard rule?

NHTSA’s July 15, 2022 final rule requires rear guards on newly manufactured trailers to prevent cabin intrusion in 35 mph crashes by compact and subcompact cars, in full width and 50 percent overlap impacts. The compliance date was July 15, 2024.

Who can be held liable for an underride crash in California?

It depends on the evidence. Possible parties include either driver, the trucking company, a maintenance provider, and the trailer or guard manufacturer. No one is liable just because an underride crash happened.

Is the driver who rear-ends a truck always at fault?

No. Insurers often start with that assumption, but a stopped truck in an unsafe spot, missing lights, or a defective or damaged guard can shift or share responsibility under California’s comparative fault rules.

Who can file a wrongful death lawsuit after a fatal truck crash?

Code of Civil Procedure section 377.60 allows the surviving spouse or domestic partner, children, and others entitled by intestate succession to sue, and in some cases certain dependents.

How long do I have to file a lawsuit after an underride crash?

The general deadline in California is two years under Code of Civil Procedure section 335.1. If a public entity may be involved, a government claim generally must be presented within six months.

Disclaimer

This page is general information for educational purposes. It is not legal advice and does not create an attorney-client relationship. Crash details are attributed to ABC7, KTLA, and the Los Angeles Fire Department as of October 14 and 15, 2026, and may change as the CHP investigation continues. No fault is assigned to anyone. Outcomes depend on the facts of each matter. Seek medical care for injuries. Consult a licensed California attorney about your situation.