If automatic driving lowers the floor of risk due to even lower risk than even the lowest risk human driver, insurance premiums will adjust to compensate and accomodate the now higher risk human driver compared to the now lower risk computer driver.

And here's the kicker: Insurance premiums don't even have to increase for the human drivers. Once owners of automatic driving cars pay even cheaper premiums, that becomes the new baseline for "cheap" car insurance and the rest should be plainly obvious. "Want lower rates? Get an automatic driving car."