Once automation gets good enough it'll probably be better at it then human drivers (imagine weaving through traffic, that sort of thing. It would also be able to do things like reroute in real time to avoid congestion.
You'll still need warm bodies in the back for life support, but I see no reason that the human in the front seat can't be replaced by sufficiently advanced technology.
Hell, in this ideal future where most or all of the rest of traffic is also autonomous, you don't even need to avoid congestion -- you just "phone ahead" along the route to tell any cars in the way to, well, get out of the way. As long as you don't have standstill traffic (which might actually be something you can eliminate as a general rule with a fully-autonomous, networked fleet), you're fine.
You'll still need warm bodies in the back for life support, but I see no reason that the human in the front seat can't be replaced by sufficiently advanced technology.