As of last year, Waymo were saying it will take up to 30 years, and they're widely considered to be in the lead:
http://spectrum.ieee.org/cars-that-think/transportation/self...
http://spectrum.ieee.org/cars-that-think/transportation/self...
But even an area that was unsuitable for self-driving cars half the time would see huge demand for self driving cars: half the time the car would drive itself, the other half it would be a regular taxi driven by a human being.
https://www.theatlantic.com/technology/archive/2017/08/insid...