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DIAMOND BAR, Los Angeles County, Calif., Oct. 9, 2026 — A crash involving a semi-truck and at least one passenger car shut down lanes on westbound SR-60 at Grand Avenue in Diamond Bar, Calif., Thursday afternoon, October 8, according to the California Highway Patrol.
Authorities said the collision was first reported just after 2:15 p.m. near the Grand Avenue overcrossing and involved a silver Scion, a semi-truck, and at least one other vehicle. Initial radio traffic described all vehicles as stopped on the right shoulder of the roadway.
The agency's incident log shows the call was upgraded roughly five minutes later from a no-injury collision to one with injuries and a unit en route. Los Angeles County Fire Department personnel also responded.
By mid-afternoon, officers had closed the right lane to traffic as crews worked the scene, and a tow truck arrived to remove a damaged vehicle. The CHP reported the vehicle was in tow by about 2:54 p.m.
The cause of the crash remains under investigation. We hope everyone who was hurt makes a full and speedy recovery.
Why Crashes Between Trucks and Passenger Cars Often Cause More Damage
A loaded semi-truck can weigh twenty times as much as a passenger car, and that weight difference shapes everything about what happens on impact. When a much heavier vehicle meets a much lighter one, the smaller vehicle absorbs most of the change in speed, even when both are traveling at similar rates before the crash.
Closing speed matters too. A truck merging, braking, or shifting lanes on a freeway creates a narrow window for other drivers to react, and the distance needed for a loaded truck to stop is far longer than for a car. Bumper height adds another factor: a truck's frame often sits above the structural crash zones built into a car's front end, so the car's safety cage, the part designed to protect the space around the occupants, may not engage the way engineers intended.
Fatigue plays a recurring role in these crashes. Commercial drivers often work long shifts against tight delivery schedules, and hours behind the wheel without adequate rest slow reaction time in the same way distraction or impairment can. According to the National Highway Traffic Safety Administration, 70 percent of people killed in large-truck crashes were occupants of other vehicles in 2023, a figure that reflects the weight and height mismatch more than any single driver's error.
Frequently Asked Questions
What are a truck's blind spots, and why do they matter?
Semi-trucks have large no-zones along both sides, directly behind the trailer, and just in front of the cab. A car lingering in one of these areas may be invisible to the truck driver, which is why safety experts advise passing quickly and avoiding driving alongside a trailer for long stretches.
What is an underride crash?
An underride crash happens when a smaller vehicle slides partly or fully beneath a truck's trailer during impact. These collisions can be especially severe because the car's upper safety structures may not make contact with the truck at all.
What typically causes large-truck collisions?
Common factors include driver fatigue, following too closely, mechanical failure such as brake or tire problems, and difficulty maneuvering in tight traffic. Weather and road conditions can also play a part.
How can drivers share the road safely with trucks?
Give trucks extra following distance, pass on the left when possible, and avoid cutting in front of a truck right after passing it, since trucks need more room to slow down.
What to Do After a Truck Crash in Diamond Bar, CA
If you're involved in a crash with a commercial truck, move to a safe area if you're able and call 911 to report injuries. Even if you feel fine, a medical check is worth getting, since some injuries from a vehicle impact don't show symptoms right away.
Exchange information with other drivers and take photos of the scene if it's safe to do so. Ask responding officers how to obtain the official collision report, since it can take time for details to be finalized. If the California Highway Patrol or county fire crews responded, their incident number can help you track the report once it's released.
