I think self driving cars will increase safety, and decrease accidents. I've read that accidents contribute for 25% of traffic congestion that exists today, so self driving cars could have a noticeable impact on decreasing drive times.
Self-driving cars must follow the speed limit at all times.
How can a company program a car to break the law?
I think following the laws and driving calmly is a great benefit. Never once I have thought, "I'm so happy that Uber driver drove like a maniac weaving between lanes, and got me to my destination all of 4 minutes earlier. Yay".