Waymo explains why its robotaxis clogged San Francisco streets during a power outage

• Waymo said on Tuesday that Saturday's power outage in San Francisco overwhelmed its robotaxis.
• The outage triggered a backlog in its robotaxi system, leading to response delays.
• The company is rolling out fleet-wide updates to improve the robotaxi's response to power outages.

Waymo has laid out what went wrong when its robotaxis stalled in San Francisco during a power outage on Saturday.

The Alphabet-owned self-driving car company said in a statement on Tuesday that its autonomous vehicles behaved as designed when intersections went dark, treating them as four-way stops. The problem was scale.

The Waymo "may occasionally request a confirmation check" when it encounters dark traffic signals to "ensure it makes the safest choice," the statement said.

"While we successfully traversed more than 7,000 dark signals on Saturday, the outage created a concentrated spike in these requests."

"This created a backlog that, in some cases, led to response delays contributing to congestion on already-overwhelmed streets," the company added.

On Saturday, some Waymo robotaxis stalled in intersections and along busy streets in San Francisco during a power outage, according to footage shared on social media. One clip on X showed at least five driverless vehicles bunched together at a junction, causing traffic congestion.

The power outage, which affected about 130,000 Pacific Gas & Electric customers, prompted Waymo to halt its ride-hailing services.

Waymo told Business Insider on Sunday that it had restarted its robotaxi service in the area.

On Monday, the California Public Utilities Commission told Business Insider it is "looking into specifics" of the incident.

Waymo said on Tuesday it had established the confirmation checks during early deployment "out of an abundance of caution," and the company is "now refining them to match our current scale."

"While this strategy was effective during smaller outages, we are now implementing fleet-wide updates that provide the driver with specific power outage context, allowing it to navigate more decisively," Waymo added.

The company also said on Tuesday that it had suspended its service in San Francisco because city officials asked for clear streets for first responders.

"This ensured we did not further add to the congestion or obstruct emergency vehicles during the peak of the recovery effort," Waymo added.

In addition to the updates that would provide vehicles with more context about power outages, Waymo said it would improve its emergency response protocols and expand engagement with first responders.

Waymo launched its driverless ride-hailing service in Phoenix in 2018 and now operates in other cities, including Austin and Atlanta, through a partnership with Uber.

In 2022, it rolled out driverless vehicles in San Francisco and made rides available to the public via its app last year.

Waymo's expansion has not been entirely smooth-sailing. In May, Waymo recalled the software affecting more than 1,200 vehicles after some crashed into chains or gates. A bodega cat in San Francisco was run over by a Waymo car, prompting outcry from residents, Business Insider reported last month.