Has Waymo expanded the list of routes significantly? Last I read about it, the number of disengagements was very low, but the cars were traveling a pretty low of number of fixed routes in areas with good weather and visibility.
They are not fixed routes at all as far as I know. It takes people where they ask to go on the app according to what I've heard. It is a geofenced area. Phoenix pretty much always has good weather and visibility that's why they are starting there.