1.0001x is definitely not acceptable because dangerous drivers bring the total-human-safety metrics down. The "average" (median, or even maybe 25%ile) driver is

1.0001x is definitely not acceptable because dangerous drivers bring the total-human-safety metrics down. The "average" (median, or even maybe 25%ile) driver is probably much less likely to be in an accident (or fatal accident)than the drivers who drive most dangerously, e.g. frequently texting while driving or driving while intoxicated. So for most drivers, 1.0001x the average human rate would actually be worse than driving themselves, although they may find the risk acceptable.