Urban Autonomy Lab
Chapter 4 · EV67

Waymo SF Power Outage — Fleet Coherence Stress Test

Date collected: 13 April 2026
Summary

Power outage disables traffic signals; Waymo suspends service; confirmation request spike overwhelms fleet response

Headline Finding

On approximately 11 April 2026, a PG&E substation fire caused a power outage affecting 130,000+ homes and businesses in San Francisco, disabling traffic signals across wide areas. Waymo proactively suspended its robotaxi service on Saturday evening, completing active trips before returning vehicles to depots. The incident revealed a fleet-level operational vulnerability: a “concentrated spike” in vehicle confirmation requests overwhelmed Waymo’s fleet response team, as many vehicles simultaneously needed human guidance.

Detail

  • Date: Weekend of 11 April 2026 (Saturday evening)
  • Cause: Fire at PG&E electrical substation; 130,000+ homes/businesses without power; widespread traffic signal failure
  • Waymo response: Proactively paused service Saturday evening; completed active trips safely; returned vehicles to depots or pulled over
  • Fleet-level issue: Waymo vehicles are designed to treat non-functioning traffic signals as four-way stops. However, the scale of the outage created a “concentrated spike” in confirmation check requests — many vehicles simultaneously contacted the fleet response team to verify their behaviour was correct
  • Capacity constraint: The fleet response team was overwhelmed by simultaneous requests, revealing that the remote assistance model has capacity limits under fleet-wide stress conditions
  • Software update: Waymo announced it will ship a software update to help robotaxis navigate disabled traffic lights “more decisively” and will update confirmation protocols and emergency response systems for large-scale disruptions
  • Mayor’s response: San Francisco Mayor Daniel Lurie praised Waymo’s response alongside police, transit workers, and emergency crews
  • Parallel to Wuhan: Unlike the Baidu Wuhan incident (EV49) where vehicles froze uncontrollably, Waymo’s fleet was proactively halted. But the underlying pattern is similar: fleet-wide infrastructure dependency (in this case, traffic signal infrastructure + remote assistance capacity) creates correlated operational risk across all vehicles simultaneously

Governance Implication

This incident is a controlled version of the Fleet Coherence failure mode. Waymo’s proactive decision to suspend service prevented a Wuhan-style cascading failure — but it also revealed that the remote assistance model has finite capacity that can be overwhelmed by correlated events. If 130,000-household power outage is enough to stress the system, what happens during an earthquake, a major weather event, or a deliberate infrastructure attack? Cities permitting large-scale AV fleets need to require operators to demonstrate remote assistance capacity under correlated stress scenarios, not just normal operating conditions. The paper should cite this as a “near-miss” Fleet Coherence event that validates the requirement for fleet-level resilience testing as a licensing condition.

Sources

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