Most of New York’s subway system still relies on antiquated technology, known as block signaling, to coordinate the movement of trains. A modern system, known as communications-based train control, or C.B.T.C., is more dependable and exact, making it possible to reduce the amount of space between trains.
A computerized signal system like C.B.T.C. is also safer because trains can be stopped automatically. New York’s quest to install the new system began in 1991, after a
subway derailment at Union Square in Manhattan killed five people. The train operator was speeding after he had been drinking.
More than 25 years later, the authority has little to show for its effort to install modern signals. The L line began using computerized signals in 2009 after
about a decade of work. A second line, the No. 7, should have received new signals last year, but the project was delayed until the end of this year.
The process is complicated. It requires installing transponders every 500 feet on the tracks, along with radios and zone controllers, and buying new trains or upgrading them with onboard computers, radios and speed sensors. The authority also had to develop a design and software that was tailored to New York’s subway.
Over the years, the authority has kept pushing back the timeline for replacing signals. In 1997, officials said that every line would be computerized by this year. By 2005, they had pushed the deadline to 2045, and now even that target seems unrealistic.
Upgrading the signals is expensive, but an even bigger challenge is scheduling work on such a vast system where ridership is always high, even on weekends, Mr. Prendergast said.
“The money issue, as difficult as it is, is an easier issue to sort than how much work can the system sustain at one given period of time,” he said.
As ridership exploded on the L line, which runs between Brooklyn and downtown Manhattan, the agency did not have enough train cars built to communicate with the new signals.
“It took way too long, but it was a confluence of things that made it take a while,” said Richard Barone, a vice president at the Regional Plan Association, an urban policy group that has
studied New York’s signals.
The authority awarded a contract for the No. 7 line work in 2010, but Hurricane Sandy struck two years later, damaging subway tracks and delaying the project. And officials have been reluctant to frustrate riders by halting train service for long stretches, leaving workers with few windows to finish the work, Mr. Barone said.
