A power outage struck San Francisco on Saturday that blacked out about 130,000 customers at its peak, according to Pacific Gas and Electric Company, but also caused another problem: stranded Waymo vehicles. Posts all over social media showed the company’s autonomous SUVs sitting still in the streets and causing traffic jams.

Some people posted videos of Teslas using their FSD feature to navigate the same streets, and Elon Musk tweeted that “Tesla Robotaxis were unaffected by the SF power outage.”

In response to an inquiry from The Verge, Waymo spokesperson Suzanne Philion sent a statement saying, “We have temporarily suspended our ride-hailing services given the broad power outage in San Francisco. We are focused on keeping our riders safe and ensuring emergency personnel have the clear access they need to do their work.” PG&E reported as of 7AM PT that “Crews have restored about 110,000 customers and PG&E continues to work on restoring the remaining 21,000 customers, primarily in the Presidio, Richmond District, Golden Gate Park and small areas of downtown San Francisco,” as it continued repairs after a fire at a five-story power substation.

Exactly why the cars weren’t moving remains unclear, with no public updates we could find on the company’s social media channels, but speculation centered on spotty wireless data connections, with cell towers either down or overloaded by people who no longer had access to Wi-Fi, and/or the street lights that weren’t operating without power.

These problems have occurred before, though, as seen in TikTok videos from earlier this year showing Waymos frozen by a malfunctioning street light and during a power outage in Austin, Texas. In a reply to a Reddit post showing another similar situation last year, someone saying they were a former employee commented explaining that the vehicle would send a request to a remote assistant and wait for their response before proceeding.

According to a company blog post, it reaches out to a human response agent when the car encounters “unique interactions,” providing them with live and recorded views from its cameras in addition to a 3D map of what the sensors are picking up. However, those may require bandwidth that’s hard to find during a significant power outage. I couldn’t find any statistics on how many remote assistance operators Waymo has available at a given time, but in November, the company announced it passed a third-party audit by Tüv Süd, a German tech inspection company that evaluated its remote assistance program against industry best practices.