SAN MATEO, San Mateo County, Calif., Sept. 29, 2026 — A multi-vehicle crash involving several Tesla models blocked lanes on southbound US-101 near Poplar Avenue Monday afternoon, September 28, according to the California Highway Patrol. Multiple people were reportedly injured, and the freeway was closed under a SigAlert for more than two hours.
The California Highway Patrol said the collision was first reported as a five-vehicle crash just before 5 p.m., with reports of injuries and at least one vehicle blocking lanes. Callers described a chain of vehicles involved, including a white Tesla Model Y, a white Tesla Model 3, a blue Tesla Model X and a black Chevrolet pickup.
Multiple patients were treated at the scene, the agency's log indicates, with at least two people reported hurt and one airbag deployment noted in a white Tesla. San Mateo County fire crews responded along with CHP units. One vehicle was reported with major front-end damage, and at least one car had to be moved off the roadway by a Freeway Service Patrol unit.
The California Highway Patrol issued a SigAlert shortly after 5 p.m. for the southbound lanes just north of Poplar Avenue, warning of extended delays as crews worked to clear multiple damaged vehicles. Several tow companies were called to the scene to remove the vehicles, and all lanes reopened by 7 p.m.
The cause of the crash has not been released and remains under investigation. We wish those injured a speedy recovery.
When Chain-Reaction Highway Pileups Are Most Likely
Multi-vehicle crashes on freeways tend to cluster around the hours when traffic volume and driver fatigue overlap, particularly the evening commute between 4 p.m. and 7 p.m. Dense, fast-moving traffic during this window leaves little space for one driver's sudden stop to avoid becoming several drivers' sudden stop, especially when following distances are already short.
Weather and light also play a role. Crashes involving multiple vehicles rise during the darker months and in conditions where glare, rain or fog cut down how far ahead a driver can see. Even without rain, low sun angles during evening commute hours can blind drivers heading west, a factor on stretches of highway that curve toward the coast.
According to the Insurance Institute for Highway Safety, 17,008 motor-vehicle crash deaths occurred outside passenger vehicles in crashes involving passenger vehicles in 2023. That figure reflects how often people outside the vehicles directly involved, including those on foot or on motorcycles nearby, can be caught up in these events.
Frequently Asked Questions
Are secondary crashes common after an initial wreck?
Yes. Once a crash blocks lanes, following traffic often has little warning, and secondary collisions happen as drivers brake late or swerve around debris and stopped cars.
What makes multi-vehicle crashes hard to investigate?
Investigators have to reconstruct impact order and timing among several vehicles, often relying on damage patterns, vehicle data recorders and witness accounts that may conflict.
What typically causes highway pileups?
Common factors include sudden braking in heavy traffic, tailgating, reduced visibility, and one vehicle's collision triggering a rapid chain of following impacts.
Why do chain-reaction crashes happen?
They occur when following vehicles can't stop or steer clear in time after the vehicle ahead suddenly slows or stops, often because of short following distances or delayed reaction time.
What to Do After a Multi-Vehicle Crash in San Mateo, CA
If you're involved in a multi-car crash, try to move to a safe area away from moving traffic if your vehicle is drivable and it's safe to do so. Turn on hazard lights and check on passengers and nearby drivers before exiting a vehicle on a live freeway.
Seek medical evaluation even if injuries seem minor. Adrenaline can mask pain from whiplash or internal injury in the hours after a crash. Get contact information for other drivers and witnesses, and request a copy of the official collision report once it's available.
Photograph vehicle positions and damage if it's safe to do so, since these details often help investigators and insurers piece together how a multi-vehicle crash unfolded.
