Except that the MTA is doing it on sections of lines at a time. It is actually not hard, because the equipment does not have to be aware of things beyond whate

Except that the MTA is doing it on sections of lines at a time. It is actually not hard, because the equipment does not have to be aware of things beyond whatever sections of track it controls (otherwise, any upgrade would require national coordination, since most rail systems, including the NYC subway, are connected to the national rail network).