[snogglethorpe]

> If and when the line is fully automated someday... Until then, human operators can't reliably get the train cars to stop in the same place.

Note that it certainly is possible to consistently do very accurate stops with only unassisted human operators; Japanese rail operators have done this as a matter of course, AFAIK using simple visual alignment aids, for as long as I can remember. [Traditionally it's done because people are lined up at the door locations (marked on the platforms), not for platform barriers.]

It's more a matter of operating culture and training than technology.

[Of course changing the latter may be easier in NYC!]