Upgrading it is slow and expensive work,but the new systems will eventually allow more trains to race on the same track.
The New York subway is stale. You see the signs every time you ride it. The paint on the cast iron pillars is layered like the rings of a tree trunk, and whether you removed the ads from the walls, and the stations would fool any time-traveler from the 1950s into thinking they were still in their own time.
Read Full tale
Source: fastcompany.com