Waymo has outlined how its autonomous vehicle service operated during a widespread power outage in San Francisco in December 2025, and the operational changes it is making as a result.
The outage, which occurred on 23 December, was caused by a failure on the network operated by Pacific Gas and Electric Company (PG&E) and affected power supply across large parts of the city.
According to Waymo, the loss of electricity disabled a significant number of traffic signals, contributing to congestion across major routes. The situation required police officers to manually manage intersections, and the San Francisco Department of Emergency Management advised residents to remain at home due to the scale of disruption.
A Waymo autonomous vehicle
© Waymo
Waymo stated that its autonomous driving system is designed to treat dark traffic signals as four-way stops. In some circumstances, the system may request an additional confirmation check to ensure a safe manoeuvre. During the outage, Waymo vehicles successfully navigated more than 7,000 unpowered traffic signals. However, the unusually high concentration of such situations led to an increase in confirmation requests, which in some cases resulted in delays and added to congestion on already busy roads.
The company explained that these confirmation protocols were introduced during earlier stages of deployment as a precautionary measure. While effective during smaller-scale incidents, Waymo acknowledged that the outage highlighted the need to adapt these processes for larger, city-wide events. As a result, the company is introducing fleet-wide updates that provide its autonomous system with broader context about regional power outages, allowing vehicles to make decisions with greater independence.
As the outage continued and city authorities prioritised access for emergency services, Waymo temporarily suspended operations in affected areas. Vehicles were instructed to pull over and park safely, before being returned to depots in stages. The company said this approach was intended to avoid adding to congestion or impeding emergency response efforts.
Following the incident, Waymo is reviewing its emergency preparedness arrangements. Planned actions include updates to how outage information is integrated into vehicle decision-making, revisions to emergency response protocols, and continued coordination with city authorities, including the office of Mayor Daniel Lurie. The company also confirmed that it will continue to update its training for first responders, building on existing programmes that have involved more than 25,000 personnel globally.
Waymo is analysing data from the event and incorporating the lessons learned into the ongoing development of its autonomous driving systems, with the aim of improving performance during large-scale infrastructure disruptions.
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