SAN FRANCISCO — When the dense, iconic fog rolled in over the residential neighborhood of Balboa Terrace on a recent Tuesday, five matching white SUVs covered in cameras ground to a halt.

Confused by the drop in visibility, the Google-owned electric Jaguar I-PACEs tried to pull over and wait out the weather — creating a brief traffic jam. But there was no one inside to yell at. The cars were empty autonomous cars run by software.