First they have to make new rolling stock, as the new system only works on post-2000s trains.

Second, MTA estimate about 16 miles of track could be upgraded per year. They have 665 miles of revenue track (850 including non-revenue), so it would take 41.56 years just to convert the revenue track. The Regional Plan Association wants MTA to convert 21 miles of track per year, leading to 31.66 years to cover all the revenue track.

Add the time to create new rolling stock, any additional time for any additional track in the next 30+ years, and extra time in case they go over the original estimation. Easily between 35 and 50 years just to convert the revenue-generating track.

https://en.wikipedia.org/wiki/Signaling_of_the_New_York_City...