That depends how many dumb drivers it takes off the road compared to normal drivers, and the relative percentages of accidents caused by each.
Let's say we have 9 normal drivers and 1 dumb driver. The 9 normal drivers cause 0 accidents per year each, and the 1 dumb driver causes 15 accidents per year. Let's say autonomous cars cause 1 accident per year. If autonomous cars replace all the drivers, there's 10 accidents per year instead of 15.
Obviously these are hypothetical numbers. All I'm saying is that if you only have one of these numbers, you don't know which kind of driver is safer.
I guess I'm just working on anecdotes and guesswork here, but I always assumed the vast majority of drivers are pretty reasonable most of the time. I imagine if this were not the case the clusterfuck on the roads would be considerably worse than what I see in practice. It is certainly true that the dumb drivers heavily outweigh the sane ones in my memories of traffic, but I also know the details of more plane crashes than successful flights.
Let's say we have 9 normal drivers and 1 dumb driver. The 9 normal drivers cause 0 accidents per year each, and the 1 dumb driver causes 15 accidents per year. Let's say autonomous cars cause 1 accident per year. If autonomous cars replace all the drivers, there's 10 accidents per year instead of 15.
Obviously these are hypothetical numbers. All I'm saying is that if you only have one of these numbers, you don't know which kind of driver is safer.