Self-driving cars have no test record in conventional commuter traffic (AFAIK). Assuming for the moment, that the cars are built so that a human driver can instantly take control of the car, I can easily see a situation where a drunk enters the car and decides that he knows better than the automated system. Or perhaps someone else who decides to change the destination when they either remember something or see a sign along the rode for free strawberries. I've read many comments by Americans who drive while on holiday in Europe because they like the idea of stopping when they see something interesting. How does a driverless car help in that situation?
And you are the idiot if you think that taking a train to a grocery store is how public transport works. Fortunately, where I live, most stores are in the same area where people live. Because the US is so obsessed with cars, many shopping centres are built in the countryside where walking to a store is no longer possible. In that situation, there should be buses, not trains.
Driverless cars, it seems to me, is the US answer to climate change. A "have your cake and eat it too" solution.
While we are here because we like technology, let's be realistic: VW, GM, etc. - would you trust them to make a flawless device that would keep you and your family safe? I wouldn't.