If self driving cars exist courts will be more likely to take away drivers licenses from those who drive while drunk. Thus I'd expect 10% of the cars being self driving to result in something like 20% less drunk drivers because such drivers are more likely to get the self driving cars - not that they want them more than anyone else but because they are not given any choice.

> If 10% of the cars are self-driving, to a first approximation there will be 10% less drunk drivers.

It seems unlikely that people who buy/use early self-driving cars have the same percentage of drunk driving as the general population. Surely employment rates would be a factor, for example.

I'm not sure whether or not there is a correlation here. Anecdotally, it seems to me there are plenty of wealthy, employed people who buy new cars and crash them after drinking.

But even if it is true that those who drive cheaper, older cars are more likely to drive drunk? Today's new cars with high-tech self driving features are tomorrow's affordable used cars. You have to start somewhere.