I've posted variants of this same comment several times and I'm starting to feel like a broken record.
Look at studies of efforts to make planes safer by removing the human element. While efforts like autopilot have made things safer it reaches the point where more automation can reduce safety as pilots are no longer alert and/or don't trust the instruments and/or can't fully manually override the automation.
Call it the uncanny valley of automation safety.
Bridging that last few percent for true automation (ie where vehicles aren't designed to have drivers or pilots at all) is going to be _incredibly_ difficult, to the point where I'm not convinced it won't require something resembling a general AI.
All of this is why I think driverless cars are going to take much longer than many expect.