The US is spread out to an extent that people in Europe have a difficult time imagining. This tends to make people car dependent, which in turn impedes public transit even where it'd work well.

The US has good train infrastructure for freight (far better than Europe), but rail service is not great. There's no good train route from the SF Bay Area to Southern California. But even if there were, getting around in the LA area practically requires a car, so you'll be renting one at the end of a train journey anyways.

So, the options to get my family down there look like:

* $100 roundtrip flight * 5 of us = $500 plus the cost of renting a car. Annoying airport logistics and luggage, and a few hours of time saved

* ~$300 of wear on vehicle and gas round trip, plus having to drive for 6 hours.

A good train would be something inbetween-- perhaps $30-40/person, but still needing to rent a car. Somewhat easier logistics, but still annoying luggage, etc. Time between that of a flight, etc.

But a self-driving car would take the worst suck out of the driving trip.