[cmsmith]

>Creating them, however, is a monumental task. There are more than four million miles of roads in the United States.

I assume that most passenger-miles are driven on <0.5MM miles of roads, moreso if they are marketing mainly to normal suburb-city commuters. And the advantage of self driving cars isn't really in the last mile. In my commuting days, I would have said

driving myself for 40 minutes <<< self driving car drives for 35 minutes and I drive for 5 < self driving car drives for 40 minutes