They will be "drivers assistant" for a decade or so at least.
Trully autonomous driving from your home to park at work is never going to be properly possible until we get smart roads which have sensors that tell the car computer what is going on. Japan just started implementing those, but it is very slow roll out.
But in the meantime, you will have cheap pre-crash in every vehicle that will make everything much safer.
This tech is not expensive - Toyota managed to bring cost of pre-crash down to $300 to customer for affordable yet good system (most right now are not good, for instance German companies have very poor performing pre-crash systems in real life). Toyota's best system costs $600 and has radar cruise control and bunch of other things.
So if that can be sold at $600 for profit, then in 6-7 years we will have same system doing "assistance" driving on its own for $1k or less.
However, fully autonomous cars as people imagine it today are vaporware right now. Hardware for 360 monitoring that can fit a car without huge sensor on top does not exist today. They are hoping it will in 3-4 years, but it doesnt today.
Google is advertising their tech through blogs but if you believed them until few weeks ago, they were saying that they never had a problem with their system. Now with state legislature making them reveal number of times driver had to take over, it is suddenly a lot more. Even then, they are making vague statements.
Here is TIME's article:
http://time.com/4179166/google-cars-self-driving-autonomous/
So one "problem" per 5318 miles. With majority of those coming from city driving, which likely means a lot more problems than that in city driving.
Now imagine that with New York traffic or any European city traffic vs freaking Mountain View.