But think about what can happen if you have a system designed to not require a driver at each subway car. You can have smaller cars, called on demand. You don't need to wait for the next car to come. This is especially a benefit during late night hours, when you might have a subway come only every 20 or 30 minutes. This is made worse if you need to transfer.
Once you get cars running along existing lines with small cars, you can eliminate subway lines entirely. Just hop in a subway car, tell it where to go, and it gets you there. No transfers, no thinking of the best lines to take, just get in a car and it'll drop you off at your end location. It would eliminate taxis for many people, which would be one of the reasons this plan would create controversy. Also controversial is elimination of conducting jobs.
I see a few reasons replacing subways will work better than trying to replace cars:
* One organization already owns all the infrastructure for a subway: they can just choose to replace it, and get the laws written for themselves.
* Rails mean you don't have to worry as much about steering, or cars next to you turning into you.