New Delhi, July 13 -- SAN FRANCISCO - Rose Peterson was inside a Waymo when it drove over a lit firework.

autonomous vehicles designed to navigate controlled conditions with remarkable consistency do not always know what to do when the real world stops cooperating.

Peterson was not alone that night. At least a dozen Waymo vehicles stalled across the Presidio neighborhood, their batteries depleted by hours of gridlock the cars could not exit independently. Some required towing. Unplanned road closures near the Golden Gate Bridge fireworks show compounded the congestion, cutting off routes that Waymo's remote assistance team would have used to recover vehicles one at a time. When hundreds of passengers are stranded simultaneously and cell...