I'm not sure why you would say there's no significant inclement weather in Atlanta. The flooding this week was not super common, but also not unheard of. It rains here a LOT in the summer

Agreed, this happens here every year, it's why we built O4W park the way it is, and built many other drainage structures similarly. We have a real runoff problem. Waymo picked a great city to train the cars on weird weather and weirder roads. :D