Here’s what we know about autonomous vehicles: They’ll be safer and smarter than the cars parked in our driveways today. Anyone who speculates beyond that is just, well, speculating.

It wasn’t long ago that a top automotive supplier was talking about providing fully driverless systems for production vehicles by 2019. Uber thought it would have 75,000 autonomous vehicles operating by this year. Elon Musk pointed in to a similar horizon in 2014 when a group of Journal editors and reporters asked him when he thought an entirely...