I personally think autonomous car will be the death nail in the public transit coffin. Once every car is autonomous, then you can picture a very efficient system, along the line of a system in the iRobot movie. If I need to be in SF the next day, I can leave SD the night before, go to sleep in the car and wake up at my destination. Why should I even bother with a train. Also keep in mind that the current speed limit is set because of human. If every car is autonomous, I’m sure it would be safe for every car to be traveling at >100MPH, since they all will know where other cars around them are and where they’re going, so there would never be any surprise.