I think the best shot for initial adoption of robocars is Singapore. As a country that's primarily a city-state, it has the sheer percentage of urban area to make adoption both easier, in just needing to get the urban area right at first for a significant countrywide impact, and more significant in terms of the country as a whole. It also has the advantage, in this case, of being a semi-benevolent dictatorship. If you can convince the government this is a good idea, it'd make a US Presidential proclamation look like something tossed into a GM suggestion box. It'd also largely avoid problems with unions and established companies. The government there does have a good track record on being tech-friendly and wanting to improve the country, and I believe they have congestion charges for the city core which provides additional incentive to do robocars.