Mass transit only works when there are masses of people, and most of the US doesn't have that. But places like the Great Plains and the rural Northeast already have comprehensive roads systems, and electric robot cars turn those roads into transit for people who, currently, must have cars.

In rural places, not only are there no buses or trains, there's hardly any taxis. Maybe during the day if you wait an hour or two, but you're not getting home at night without your own car.

A couple robot taxis roaming around every rural country in the US comprehensively solves this problem.

This is true for intersection throughput, but I bet full travel throughput (walking to the bus, waiting for the bus/train, walking to your destination) is the same or better with Waymo.