Re: Tesla never said it's driverless
...and it's also why (paradoxically) reducing speed limits on roads without also making those roads deliberately more challenging (narrower, etc.) can increase risk of fatal collision with bystanders. You can observe this yourself if you like -- find a nice clear stretch of road designed for high speeds, and try to maintain 10KPH for half an hour while staying completely attentive on your slowly changing environment.
Or just come to Norway for a driving holiday. Super slow speed limits, and super slow (and quite bad) drivers.
When I'm stuck behind another driver I often catch myself wondering how I got to where I am (after a few minutes of my mind wandering from abject boredom). When the road is clear and I'm driving at full fart (as the Norwegian expression goes) I'm much more attentive and aware of my surroundings.