I find it odd the way people talk about moving through the levels sequentially without really acknowledging there's a massive phase change that happens somewhere between level two and four, where a self-driving car could easily be way more dangerous than the average human driver.

That comes as soon as you have a situation where the automation has to be able to handle all foreseeable scenarios without failing because the human is no longer paying attention.

It's a fixture of complex adaptive systems analysis that one encounters scenarios where having anything short of perfection is just as good as useless. The implicit assumption in this post is that there are linear returns to incremental progress. That's not necessarily true at all.

It's quite possible -- I would argue likely -- that we'll be very tantalizingly close-but-not-good-enough to full automation for a decade or three before we actually change the fundamental nature of transportation.