I haven't found US figures, but for the UK, motorway driving has a far lower fatality rate than non-motorway driving. "Although motorways carry around 21 per cent of traffic, they only account for 6 per cent of fatalities and 5 per cent of injured casualties. In 2015, the number of fatalities on motorways rose from 96 deaths to 110."[1] Since Tesla's "autopilot" is only rated for motorway (freeway) driving, it should be compared against motorway fatality rates, which are about a third of general driving rates. So a realistic estimate of the fatal accident rate for human freeway driving is maybe 0.3 per 100 million miles driven. Tesla is doing much worse than that.
To rate an automatic driving system, you want to look at accident rates, not fatality rates. Accident rates reflect how well the control system works. Fatality rates reflect crash survivability. Tesla needs to publish their crash data. That's going to be disclosed, because the NHTSA ordered Tesla to submit that information.