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SUN VALLEY, Los Angeles County, Calif., Sept. 18, 2026 — A sedan and a semi-truck collided Thursday morning, September 17, on I-5 northbound near Sheldon Street in Sun Valley, according to authorities. The crash sent at least one vehicle to the roadside shoulder and prompted a response from fire crews and the California Highway Patrol.
Authorities said a black Mercedes-Benz sedan reportedly rear-ended the semi-truck after an unsafe lane change. A person who reported the crash told dispatchers both vehicles had pulled to the shoulder.
The driver who called in the crash requested medical response for injuries, according to dispatch logs. Los Angeles Fire Department units, an ambulance and CHP officers responded to the scene, along with a Freeway Service Patrol unit that assisted before closing out its portion of the response around 8:01 a.m.
The California Highway Patrol is investigating the cause of the crash. We wish the injured a speedy recovery.
Why Rear-End Crashes With Trucks Turn Severe So Fast
A rear-end crash involving a semi-truck plays out differently than one between two passenger cars. When a sedan strikes the back of a trailer, the car's hood and windshield can slide underneath the trailer's frame instead of crumpling against a similar-height bumper. That underride motion lets the trailer's structure reach into the passenger compartment, because the two vehicles don't meet at matching heights.
Unsafe lane changes near a truck's blind spot are a common trigger. A car that cuts in front of or beside a truck and then brakes, or misjudges following distance, can end up in a rear-end situation before the truck driver has room to react. Trucks also take longer to slow because of their weight, so the closing speed at the moment of impact is often higher than drivers expect.
Rear guards and reflective markings on trailers are designed to reduce underride, but they don't eliminate it in every impact angle or speed. According to the National Highway Traffic Safety Administration, an estimated 153,452 people were injured in traffic crashes involving large trucks in 2023.
Frequently Asked Questions
What is an underride crash?
An underride crash happens when a smaller vehicle collides with a truck or trailer and slides partly or fully beneath it, because the vehicle's frame sits lower than the trailer bed.
What typically causes large-truck crashes?
Common factors include unsafe lane changes near trucks, following too closely, driver fatigue, and misjudging a truck's stopping distance or blind spots.
Does driver fatigue play a role in truck crashes?
Yes. Long hours behind the wheel can slow reaction time for both truck and passenger-vehicle drivers, and fatigue is a recurring factor cited in crash investigations nationwide.
How can drivers share the road safely with semi-trucks?
Leave extra following distance, avoid lingering beside a trailer's blind spots, and signal early before changing lanes near a truck so the driver has time to react.
What to Do After a Truck Collision in Sun Valley, CA
If you're involved in a crash with a semi-truck, move to a safe area if possible and call 911 to report injuries and get police on scene. Even if you feel fine, ask for a medical evaluation, since some injuries from a rear-end or underride impact don't show symptoms right away.
Get contact information from the truck driver and any witnesses, and photograph the vehicles and the scene if you're able to safely. A CHP or local police report will document the incident, which matters for insurance and any follow-up investigation. Keep any paperwork from the responding agency and follow up with your own doctor in the days after the crash.
