From what I've seen in ai-class.com and cs373 on udacity: The cars are completely autonomous. The only reason there's a human in the driver's seat is legislation because it's mandatory that there is a person in the driver's seat.
But, the cars are already at the stage where you can feel safe just reading a book while sitting in there. They work in normal San Francisco traffic without any intervention at any time by the human.
They even plan their own routes and can change them when something strange happens on the road so they're forced to take a detour. They even wait for pedestrians crossing streets, follow all traffic rules and so on.
It's really quite amazing when you think that just 8 years ago the DARPA challenge wasn't finished by a single car that entered the race. (and that was without traffic, just a desert with roads)
A little side note, riding in the desert might seem like a no-brainer, but it's really really really hard for a computer to make sense of the terrain or what's ahead, which is why it took some time for the first cars to even finish the race. A lot of the technology that has been developed just to make sense of the terrain is now used to keep track of pedestrians, other cars and obstacles.
But, the cars are already at the stage where you can feel safe just reading a book while sitting in there. They work in normal San Francisco traffic without any intervention at any time by the human.
They even plan their own routes and can change them when something strange happens on the road so they're forced to take a detour. They even wait for pedestrians crossing streets, follow all traffic rules and so on.
It's really quite amazing when you think that just 8 years ago the DARPA challenge wasn't finished by a single car that entered the race. (and that was without traffic, just a desert with roads)