What kind of efficiency are you discussing? What are you comparing? Roaming driverless taxis are not more energy efficient and they are not more space efficient than transit. Being an improvement on human-driven cars is not a particularly difficult achievement.

I have no idea where the car accidents or pollution sentence came from. I'm "rooting" for less cars, not the least because it will reduce pollution, and live my life accordingly. I try to minimize the disease in my life by minimizing my car use - automated or otherwise - rather than addressing the symptoms using a new wundertechnology. I don't control the number of car accidents because I can't control the choices others make.