[Retric]

Self-driving cars seem to be ~1:1 with driver licenses. A licenced driver drives at most one car at a time.

[jeffdavis]

There's obviously a connection between driver's licenses and miles traveled, but if you have the latter number, why use the former? It makes the benefit more obscure and reduces the accuracy (for instance, if passengers of self-driving cars drive more or less than passengers of human-driven cars).

Also, it doesn't offer a good way to compare against things like air travel.

[maxerickson]

There is a sense in which the part of a self-driving car that is licensed will be driving many cars at once.

(There will of course be something like 1 instance of it per vehicle, I'm commenting on the semantic awkwardness, not trying to be pedantic)