Driving assistants would improve safety certainly, but removing the driver and letting the assistant drive will need real world like tests, for now maybe you could have an independent group monitoring a number of Teslas and checking each time a human intervened and give a score on how bad the AI was.
Level 4 for example could be a blood bath, where cars drive all the easy situations, and hand over emergency control to out of practice drivers barely paying attention at a moments notice.
I believe our driving skills were better when we had manual transmission, and were more involved in overall operation. Hard to determine if safer, b/c of advances in crumple zones, airbags, etc as manual declined.
Level 4 requires that the vehicle safely stop in situations it can't handle.
The extremely sad part is that we could reduce the number of deaths until true AI arrives using simple tech that could detect if the driver is drunk or tired, and controversially forcing the speed limits(the car knows that this road is max 90Km/h and that the driver has less then 1 year experience so it will not let you get over 70 (local laws apply) unless you activate emergency mode - this would trigger some bad consequences if it was no emergency)
However I do pay attention and keep my hands on the wheel, I think autopilot + human is much safer than either one, but since the latest updates I rarely have to take control if not going in roundabouts or junctions.
I also had one instance a few weeks ago where I tried to enter another lane manually and the car took control from me and put me back in my lane as there was someone in my blind spot without their headlights on so I didn't see it.
I had two crashes in my lifetime. Both occurred when driving backwards out of a parking lot. No fatalities, limited damage. Good luck finding such situations while driving on a highway...
(that's data from the highest crash rate country where you were able see so many crashes that you develop a feel)
With AutoPilot, Without AutoPilot but With Active Safety Measures, Without AutoPilot or Active Safety Measures, and NHTSA Average Vehicle