The answer to this question comes from denying the assumptions.
If you are driving on a one-way road next to a cliff. Then visibility is X feet.
If you cannot stop in X feet, you are going to fast, slow down.
This continues until you are safe, or you have stopped.
And the answer, if you include "all of a sudden" into the scenario is to brake as hard as you can. It is the least damaging thing you can do. The other option is to turn the car into a known deathtrap. In case of emergency, the passengers will be terminated.
Turning the car into a known deathtrap for it's owners on emergency seems like a good way to turn people away who would want to buy these cars. I think the car should kill the other people, and not it's master :) How else will the loan ever be paid off then for the car? lol. Breaking as fast as it can sounds like the best option, but I think this would be a rare edge case to program for.
This is the best answer!!! Do autonomous cars travel at the posted speed limit or do they take into account for visibility?