Waymo updates software after robotaxis stalled in San Francisco

Waymo is shipping a software update to help its robotaxis navigate disabled traffic lights during power outages more decisively. The update follows a power outage in San Francisco on Saturday, where Waymo’s robotaxis got stuck during the power outage. The company explained in a blog post published on Tuesday that its self-driving system treats dead stop lights as four-way stops, which is intended to allow the vehicles to navigate intersections normally during blackouts.

However, during the Saturday outage, many vehicles requested a confirmation check from Waymo’s fleet response team to verify their path forward. While all Waymo robotaxis are equipped to perform these confirmation checks, the widespread nature of the blackout triggered a concentrated spike in confirmation requests. This sudden surge in human verification requests overwhelmed the system and led to congestion caught on video. Waymo acknowledged that navigating an event of this magnitude presented a unique challenge for autonomous technology.

Waymo noted that it originally built this confirmation request system out of caution during its early deployment phase, but is now refining the protocol to match its current operational scale. Despite the localized bottlenecks, the company asserted that its vehicles successfully traversed more than 7,000 dark signals on Saturday. To prevent similar issues, the new software update will provide the fleet with specific power outage context and regional outage data, allowing the vehicles to operate more independently. Waymo also stated that it will improve its emergency response protocols by incorporating lessons from the event. According to the company, “While this strategy was effective during smaller outages, we are now implementing fleet-wide updates that provide the [self-driving software] with specific power outage context, allowing it to navigate more decisively,”.

This software adjustment is the latest modification Waymo has had to make to its autonomous driving system. The company previously had to deploy software updates to address how its vehicles interact with school buses. Those earlier issues prompted a National Highway Traffic Safety Administration (the US auto safety regulator) investigation and led to a recall.

Why it matters

This incident highlights the ongoing challenge of scaling autonomous fleets in complex, unpredictable urban environments where edge cases like power outages can trigger system-wide bottlenecks.