Maybe you should try reading the article?

from the article:

"Many stations like this one are not prepared to accommodate a larger volume of passengers, even if a new traffic control system allowed trains to come more frequently."

"Much of the subway’s signal system uses antiquated parts like the electromechanical relays shown above from the West Fourth Street-Washington Square station in Manhattan.

Train traffic for about two-thirds of the subway system is monitored in rooms like the one shown below at West Fourth Street. Little has changed in a century.

The old signal system uses a network of switches and cables along the track to keep trains a safe distance apart. The technology is outdated and expensive to maintain."