Whether driving below the posted speed limit is safer than driving with a somewhat faster flow of traffic is a fuzzy, very contingent question.

Think about all the drunk drivers. All the exhausted drivers. Those on their phone. Those in an emotional state that is overwhelming. All the hundreds and hundreds of reasons people do a bad job of driving.

Being better than off of those is not hard, and the data shows Waymo are already there.

Not that the speeding is justified, but I would still bet on the computer continuously processing multiple video feeds reacting and stopping quicker than a human in almost all incidents.