one obstacle is driverless cars can mistake harmless puddles of water as pot holes and slow down for no reason.
there's also going to be skeptical people. considering that driverless tech has the greatest chance of reducing accidents when it’s on the road with other driverless tech, perhaps the biggest obstacle to the goal of accident prevention will be the stubborn relative or neighbor who “just doesn’t trust those things.”
also, there might be someone not paying attention in their driverless car, and the technology might not be all there. what i mean by this is they detect little animals and swerve really fast and hit another car. even though people are working on this to try and stop car accidents from happening, it could lead the the exact opposite.