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DIAMOND BAR, Los Angeles County, Calif., Sept. 23, 2026 — A three-vehicle crash involving a car reportedly traveling the wrong way injured multiple people on Tuesday afternoon, September 22, on southbound State Route 57 at Grand Avenue, according to the California Highway Patrol.
The crash was reported around 3:26 p.m. and initially involved two vehicles blocking lanes of southbound SR-57, the CHP said. Within minutes, callers reported a vehicle facing the wrong way in the middle lanes and a third vehicle involved, expanding the collision to three cars: a white Mercedes-Benz E300, a white Jeep Grand Cherokee, and a gray Toyota SUV.
Callers described damage to at least one vehicle's right side and a car left facing traffic in the middle lane, the CHP reported. All involved vehicles were later moved to the road shoulder as officers worked to clear the scene.
The extent of injuries has not been released. The CHP listed the incident as a collision with unknown injuries before updating it to reflect that at least one party required medical attention, though specific injury counts were not made public. The agency closed its response to the incident by late afternoon.
It remains unclear which vehicle was traveling the wrong way or what led to the collision. The CHP has not released the cause of the crash, and the investigation is ongoing.
We hope everyone who was hurt makes a full and speedy recovery.
How Investigators Piece Together a Wrong-Way Crash
A wrong-way collision often starts as a confusing scene, with callers giving conflicting descriptions of how many cars are involved and where a vehicle entered traffic against the flow. Officers arriving on scene first work to secure the roadway, treat anyone hurt, and move damaged vehicles before they can begin reconstructing what happened.
Reconstruction relies on physical evidence: skid marks, points of impact, vehicle data recorders, and witness statements gathered separately so accounts can be compared. Investigators also look at nearby ramps and interchanges to determine where a driver may have entered against traffic. This work can take days or weeks, especially when multiple vehicles and lanes are involved.
Agencies typically withhold names until relatives have been formally notified, a step that can take time if contact information is limited or a phone number on file doesn't work. Toxicology results, when relevant, often take several weeks to come back from a lab, and a final, complete report may not be issued until that testing is finished and all evidence has been reviewed.
According to the AAA Foundation for Traffic Safety, older drivers had a higher risk of fatal wrong-way crashes on divided highways from 2014 through 2023.
Frequently Asked Questions
Does alcohol play a role in wrong-way crashes?
Impaired driving is a common factor in wrong-way crashes nationally, though it is not confirmed in every case, and investigators typically wait for toxicology results before drawing conclusions.
Are wrong-way crashes more common on certain roads?
They tend to cluster near highway interchanges, off-ramps, and divided roads where a driver can mistakenly enter an exit ramp or the wrong side of a freeway.
What causes wrong-way crashes?
Common factors include impairment, driver confusion at interchanges, poor visibility at night, and medical or age-related issues affecting a driver's judgment.
Why are wrong-way crashes so often fatal or severe?
Because vehicles are colliding head-on rather than in the same direction, combined speeds are far higher than in a rear-end or sideswipe crash, increasing the impact force.
What to Do After a Wrong-Way Crash in Diamond Bar, CA
If you're involved in or witness a wrong-way crash, call 911 immediately and, if it's safe, move to the shoulder or a protected area away from moving traffic. Freeway shoulders and middle lanes remain dangerous even after a collision, so stay alert for other vehicles.
Seek medical evaluation even if injuries seem minor at first. Adrenaline can mask pain from whiplash, head impact, or internal injury, and some symptoms don't appear until hours later.
Cooperate with CHP officers at the scene and get a copy of the incident or case number for your records. If you're a passenger, witness, or nearby driver, write down what you saw as soon as possible, since detailed memories fade quickly and can help investigators reconstruct the sequence of events.
