I was thinking about the accident some more, and the control interface with the cruise control and autopilot seems like something interesting that hasn’t been mentioned. I have no idea how they got the car moving, or kept it moving, with no driver. Perhaps starting driving, then engaging autospeed or autosteer, and then leaving the driver’s seat. As said, if no butt in the seat doesn’t disable everything as soon as possible, then it’s a serious oversight. No butt in the seat of stopped car will put it in park.
Anyway, some background. In the Model S cruise control and autosteer are managed with a stalk on the left side of the steering wheel below the turn signal lever. Pulling the stalk towards the driver once engages cruise control, and a double pull engages autosteer/autopilot/FSD (whatever is available on that particular car and at that particular location). Pushing the stalk away from the driver disables all automatic control.
Pushing up on the stalk a small amount adds 1 MPH to the cruise control set speed. Pushing up all the way adds 5 MPH to the set speed. The set speed is decreased for pushing down.
In Autopilot on a freeway the speed can be increased up to 90 MPH or something. In autosteer or FSD on a surface street the speed can only be increased 5 MPH more than what the car thinks the speed limit is. If only cruise control is enabled (not autosteer or FSD) then the cruise control speed can be increased to 90 MPH or whatever. This, to my scenario is the key point.
So, the guy gets the car moving, puts it in autosomething mode, and jumps into the backseat. Then, perhaps because the car doesn’t have FSD, it doesn’t bother to follow the road, so somebody reaches over to turn things off with the stalk. From the awkward position in the back seat or the passenger seat, they manage to instead increase the set speed. Multiple times. So with each additional grab, the car is going 5 MPH faster, and is out of control. Perhaps the speed was increased on purpose.
Normally autoeverything can be disengaged by pressing the brake, but that’s not possible in this case.
What makes me suspect the car was never in autosteer is the 5 MPH over the speed limit restriction in that mode. It is absolutely possible that the car thought they were on a 65 MPH road, but I’ve never seen that error. I have seen the car think the speed limit is lower than posted.