On an individual basis, AVs should present an improvement in safety - but if you were to broaden that critique to how a platoon of AVs operate in mixed traffic (i.e. AV and non-AV), I think there's more reason for caution. We all have different driving habits, and the question becomes to what extent AVs are reactive and predictable to individual circumstances and how that relates to the flow of a larger network. So to give an example of what I mean - I'm from Mass and there are a number of merge intersections that I drive through occasionally that people who know they're going will act outside the prescribed traffic pattern, but they do as a means of optimization. If I know there's a chokepoint coming up ahead, I'll take a longer arc to get a place in the turn lane, whereas many people will take a shorter turn and barrel head-on into a chokepoint - how will an AV handle that intersection, how will the AV handle people who optimize their movements outside the bounds of the road design, how will AVs handle people that are protective of their lane and not willing to let a car merge - those are all important questions, particularly in places where road designs are more a function of pre-auto historical development than auto-centric development.

I have a lot of worries about the way AVs are talked about in the public sphere - but I won't get in to that (tl;dr it's not revolutionary, they don't offer structural change - it's mere technological optimization that's could easily exacerbate our transportation issues, not solve them) - but I think it's an important point to note that AVs do not offer a seamless interaction with other drivers, and that no computer model is going to be able account for abilities of human driver to react to unconventional circumstances. If the only way AVs can succeed is when private operators are eliminated from the road network, then that should give us pause about what the actual potential for implementation is.