Signaling of the New York City Subway

Most trains on the New York City Subway are manually operated. As of 2022^[update], the system currently uses automatic block signaling, with fixed wayside signals and automatic train stops. Many portions of the signaling system were installed between the 1930s and 1960s. Because of the age of the subway system, many replacement parts are unavailable from signaling suppliers and must be custom-built for the New York City Transit Authority, which operates the subway. Additionally, some subway lines have reached their train capacity limits and cannot operate extra trains in the current system.

There have been two different schemes of signaling in the system. The current scheme is used on all A Division and B Division lines, originally built to the Brooklyn–Manhattan Transit Corporation (BMT) and Independent Subway System (IND)'s specifications. An older system was previously used on all of the A Division, but with the conversion of the IRT Dyre Avenue Line signals to the B Division scheme in September 2017, this system is no longer in use.^[1]: iv

As part of the modernization of the New York City Subway, the Metropolitan Transportation Authority (MTA) plans to upgrade and automate much of the system with communications-based train control (CBTC) technology, which will automatically start and stop trains. The CBTC system is mostly automated and uses a moving block system—which reduces headways between trains, increases train frequencies and capacities, and relays the trains' positions to a control room—rather than a fixed block system. The implementation of CBTC requires new rolling stock to be built for the subway routes using the technology, as only newer trains use CBTC.