I've personally logged 2,096 miles on Waymo in the Phoenix market.
One day, Waymo was accelerating out of a driveway and onto a 7-lane stroad with 35mph limit. Suddenly, it pulled over and stopped completely on the shoulder. As other cars sped by us obliviously, I looked around to figure out why Waymo had acted out.
There was a school bus on the opposite side of the street, with its red flashers on and children nearby. The Waymo was the only one to obey or even acknowledge it.