Self Driving Cars

What companies are working on developing self driving cars? 
google is working on self driving cars

What obstacles must be overcome for self driving cars to become a reality?
tech errors where the sensors can't see the whole road

Are self driving cars safe?
no they are not completely safe yet

How would a world with self driving cars be different than the world we live in today?
the world would be different with self driving cars examples:
no more dui's,speeding,and road rage