One huge missing piece is software reliability. Don’t get me wrong, it has improved a lot. But the blunt fact of life is that most software writing systems are bloated beyond any single human’s ability to review.
Even NASA’s methods of software review have had glitches. Multiply space craft software hundreds of thousands of units run by the randomness of at least that many owners and mechanics who may not understand all the various sensors. Don’t forget all the older cars driven by people who may not be at their best behind the wheel.
This is a recipe for software failure at some level. And once that software fails, you have a case for innumerable class action lawsuits from legions of bored attorneys looking to make a name for themselves.
Also don’t overlook the possibility that someone may hack the coordination or radar channels used by these vehicles to stay in a convoy.
We will need careful legislation and standards before cars becomes completely driverless. I’m not suggesting that it can’t work. It will certainly be an improvement over human beings. However, we will need careful legislation and consideration of how much liability should be assigned to a car manufacturer in the event that someone gets hurt or the car damages expensive property.