A subway's signal systems is like its nervous system. It provides instructions to trains so they know when they can and cannot move, how fast they should move, and where our track switches are set to route trains. These systems are designed to keep trains spaced at safe distances and ensure they cannot move in ways that could put anyone in danger. You may think of signals as the devices that look like traffic lights on our tracks. In reality, they’re a complex system with multiple components that help keep our trains moving safely.
Here's how we're modernizing them.
Our legacy signaling system relies on technology that dates back to the opening of the subway over 117 years ago. While we’ve made improvements to modernize our signals over the decades, the fundamentals remain unchanged. Newer, modern signals provide our riders with faster, more frequent, smoother, and more reliable service.
To make this a reality, we’ve been replacing our existing signaling system with the international gold standard of signaling systems. Known as Communications-Based Train Control (or CBTC), our new signal systems use wireless connectivity to keep trains in constant contact with a centralized system that controls their movement.
The elements of a CBTC system
Right now, we know where a train is only because of its physical connection with the track. When the train’s steel wheels make contact with the steel rails, it breaks an electrical circuit that tells the signaling system a section of track is occupied. The system then prevents the following train from entering the occupied section of track.
With CBTC, we have equipment on both trains and along the tracks (we call this “wayside”). Trains communicate with wayside equipment that connects back via a private network to servers at our Rail Control Center.
CBTC is a complex system that combines hardware, software, and the communication links between them to deliver better train service.
These are the components of a CBTC system:
- Wayside equipment (zone controllers, radios, and transponders): These are installed on/near tracks to communicate with trains to determine their precise location and provide them with instructions about how to operate
- Car-borne equipment: Computers on trains communicate wirelessly with the wayside equipment and control train movement based on instructions from the system
- Data communications links: Our own private fiber network connects wayside equipment to servers at our central Rail Control Center
- ATS (automated train supervision) system: A computer system gives trains directions about how fast they can run, where they can run, and moves track switches to direct train traffic
- Legacy signal system: We leave the existing signal system in place so trains not equipped with CBTC (such as work equipment) can use these tracks, if needed. The legacy system is connected to the CBTC system so we can monitor these non-CBTC trains' movement.
How CBTC moves us forward
Today's signals: Fixed-block signaling
With our legacy signal system, all we know is that some part of a train is in some part of a section of track. These sections can be over 1,000 feet long! By contrast, with CBTC, we know a train’s precise location within inches.
Because we know more precisely where trains are, we can run them more closely together, safely. If trains run more closely, they can run more frequently. If trains run more frequently, our system can move more people on less crowded trains.
Drawbacks of fixed-block signaling
- We don’t know the exact position or speed of a train, so we have to run them farther apart to create a safety buffer.
- Our current system relies on a lot of infrastructure that’s expensive to install and maintain. In some cases, we are one of the only transit agencies still using the components in our signaling system. This means we either need to pay a lot of money to acquire replacements or fabricate them ourselves.
- The circuitry and electro-mechanical relays that underpin our signal block system are delicate and require more maintenance.
CBTC's advantage: Moving-block signaling
Communication-based train control, or CBTC, relies on a moving-block system. Equipment on trains and tracks tells us exactly where a train is, so we can operate trains more closely together.
Benefits of CBTC
- More efficient service. Because we know exactly where trains are on the track, we can run them closer together. The line and the lines, which both use CBTC, are our best-performing lines. On-time performance on our existing CBTC lines is consistently near or above 90%.
- Lower operating costs. Accelerating trains is expensive, so intelligently controlling the speed of trains saves us money. Maintenance is also cheaper with CBTC because it isn't as hardware intensive and software can be upgraded as technology improves.
What it takes to build a CBTC system
We’re converting existing lines to CBTC, which is more complicated than building a new train line with CBTC from the start. Before we can build the system, we need to fully plan and design all of its components.
This can be a years-long effort that involves:
- Surveying an entire line to understand its existing assets and converting that into a database
- Determining locations for wayside CBTC equipment
- Retrofitting our existing trains with onboard CBTC equipment that connects them to the larger system and provides trains with operating instructions
- Installing wayside equipment on/near tracks and connecting it back to the centralized CBTC system
- Customizing the software used to run trains to determine operating rules and service specifications (How often do trains run? How fast do they go?)
- Creating a plan to transition from a traditional signaling system to CBTC
- Testing the system exhaustively under various scenarios to find failure points and make adjustments so service runs safely/efficiently
How CBTC improves your experience
Faster service. Running trains closer together helps us increase capacity on a line. Trains can also travel at higher speeds without compromising safety.
More reliable service. Signal problems are among the leading causes of delays in subway service. Upgrading our technology means fewer issues, and when delays happen, we’ll be able to get service back on track more quickly.
A smoother ride. The computerized automatic train operation (ATO) system means there are fewer variations between how train operators run trains. Acceleration and braking is controlled by the system so customers can expect more consistency and improved performance.
More accurate arrival information. CBTC gives us much more precise information about where a train is in the system. This improves the accuracy of the real-time arrival information you see in stations and apps.
When we install CBTC, performance improves
CBTC came to the Flushing line in November 2018 and since implementation, customers have experienced vast improvements in their train service. Weekday on-time performance rose from 68.1% in 2018 to 94.9% in October 2020. Compared to before CBTC, trains run 7.8% faster on the local track and 13.5% faster on the express track, on average.
What is CBTC?
Where we’re installing CBTC
The Culver Line, on the
CBTC is coming to the in Brooklyn between Church Av and West 8 St in Coney Island.
The Queens Blvd Line, on the
We're in the final stages of testing CBTC so it can be put in service in early 2021.
The line on Eighth Avenue
We’re in the early stages of designing a CBTC system between 59th Street in Manhattan and High Street in Brooklyn.