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DIAMOND BAR, Los Angeles County, Calif., Sept. 20, 2026 — A chain-reaction crash blocked lanes on eastbound State Route 60 at South Diamond Bar Boulevard late on Saturday night, September 19. The collision reportedly grew from an initial two-vehicle wreck into a three-vehicle incident within minutes.
According to dispatch logs, the crash was first reported as a two-vehicle collision involving a white pickup truck and a gray Jeep stopped in the middle lanes of the freeway. Los Angeles County Fire Department personnel on scene told authorities the incident became a three-vehicle collision after one vehicle struck others while they were blocking lanes.
A caller reportedly told dispatchers that another vehicle, described as a black SUV with an unknown license plate, may have been involved and possibly left the scene before authorities arrived. That report was unconfirmed as of the log's close. A black Kia Sorento SUV was later reported stopped on the right shoulder in connection with the crash, though its role has not been confirmed by officials.
The crash blocked the middle lane and the number 2 lane on eastbound SR-60, and a report of another unknown vehicle blocking the HOV lane was still being verified. A tow truck was requested to clear the scene. The extent of injuries has not been released, and no further details on those involved have been made public.
The California Highway Patrol has not confirmed a cause. The incident remains under investigation.
We wish those injured a full recovery.
What Makes a Multi-Vehicle Freeway Crash So Damaging
A crash on a freeway like SR-60 does more damage than one at lower speeds, mostly because of closing speed, the gap between how fast vehicles are moving when they meet. At highway speeds, a vehicle that slows or stops in a travel lane becomes an obstacle that trailing traffic may have only a second or two to react to. That short window is usually the difference between a driver braking safely and a driver striking the stopped car.
Weight and vehicle type also matter. A pickup truck striking a smaller passenger vehicle transfers more force than two similarly sized cars colliding, because the heavier vehicle keeps moving with more momentum after impact. Bumpers and crumple zones are built to absorb some of that energy, but they are designed around a certain range of speed and mass. Beyond that range, more force reaches the passenger compartment instead of being absorbed by the frame.
Multi-vehicle pileups add another layer: once a vehicle stalls in a live lane, it can be struck again by following traffic before anyone has a chance to move or get clear. According to the National Highway Traffic Safety Administration, 28,595 large-truck occupants were injured in multi-vehicle crashes involving large trucks in 2023. Safety equipment like seatbelts and airbags reduces the risk of injury in a single, direct impact, but it cannot fully offset the added force of repeated hits from multiple directions.
Frequently Asked Questions
Why does following distance matter so much on freeways?
Following distance is what gives a driver time to react. At highway speeds, even a small gap closes in a fraction of a second, so more space between vehicles gives more time to brake or steer clear if traffic ahead slows suddenly.
Are secondary crashes common after an initial wreck?
Yes. Once a crash blocks a lane, following vehicles that don't see it in time can strike the stopped cars or each other, turning a two-vehicle incident into a larger pileup, similar to what was reported here.
What makes multi-vehicle crashes difficult to investigate?
Investigators have to determine the order of impacts, which vehicle struck which, and whether any vehicle left the scene before help arrived. Conflicting witness accounts and limited camera coverage on freeways can make that timeline harder to reconstruct.
What to Do After a Multi-Vehicle Crash in Diamond Bar, CA
If you're involved in a freeway crash, try to move to the shoulder or a safe area if your vehicle is drivable, and turn on hazard lights to warn oncoming traffic. Call 911 to report the crash and request medical help if anyone feels hurt, even if injuries aren't immediately obvious.
Stay in a safe location away from moving lanes while you wait for CHP or fire personnel to arrive. Exchange information with other drivers if it's safe to do so, and get checked by a medical provider afterward, since some injuries from a collision don't show symptoms right away. Keep a copy of the CHP incident report for your records once it becomes available.
