First, some baselines: humans suck at driving too. Next, coverage isn't an all or nothing thing, it'd be quite easy for an autonomous uber like service to restrict itself to areas that permit remote control when cars need assistance. Last I'd encourage reading some of the literature behind what folks are doing: it's a very different sort of system, one that blends a lot of complex probability estimates. It's not like everyday coding where a human developer needs to anticipate every combination of corner cases.