This is a listing of some of the more common signals found in the New York City subway system. If you find any not listed that you've seen while riding the front of a train, drop me an E Mail to Joseph D. Korman and I'll add it to this Web Page.


----------How Signals Work
----------How Grade Time Signals Work
----------How Station Time Signals Work
--------------------DeKalb Ave
--------------------Original IRT
PATH Grade Time and Interlocking Signals


There are two major types of signals used in the subway -


These signals are normally green and turn red after the FIRST CAR of the train the train passes it. Most of them have Green on top, Yellow in the middle and Red on the bottom. On some IRT lines the red and yellow are reversed.

Diagram showing how signals work with the red signals behind the train and the position of the stop arms.

Every signal has a number plate that contains identfying information. See the Chaining Page for information about these ID codes.


These signals can be generally identified as having two sets of colored signal lights.

These signals control the movement of trains through track switches and are normally red. After the tower operator sets the track switches for the train, he/she clears the signal so the train may proceed.

All interlocking signals have a number plate like - The X denotes that this is an interlocking signal This signal is cleared by moving lever 14 to the LEFT.

Union Turnpike Interlocking machine (now out of service)

Train Operator Route Selection
Probably beginning with the reconfiguration the DeKalb Ave station and interlocking in the late 1950s, the TA began a very long term consolidation of local signal towers with a limited group of master towers. With this, junctions were taken out of direct view of the towers so another means for the train operators to let the tower know the route of the train. To do this, train operator route selection "punch boxes" were placed at the station prior to the junction and at the home signal controlling the interlocking. The system installed at DeKalb can keep track of trains from six locations: Canal, Grand, Lawrence, Atlanitc, and local and express at Pacific and notify the tower so they can set the routes properly.

The next logical step in the consolidation plan was to allow the train operator punching in the route, to automatically set the switches and clearing the signals. One of the earliest was at 47-50th St/6th Ave where trains to uptown and Queens had the switches to 57th St added in 1968.

Train Operator Punch Box on track D-1 at Queens Plaza (southbound local) from before 2010 when the V train was operating between Continental and Second Ave.


IDENTRA was a switch control system that was used on the IRT Flushing line through at least the 1970's. Each cab at the ends of the train had a flat doughnut shaped antenna attached outside the car at the in front of the train operator cab. Inside the cab was a switch that allowed the operator to identify the train by express/local and destination. This is an article from the April 1954 issue of Railway Signals and Communitcations and a map/diagram .

The wayside was equipped with readers at the height of the antenna that read the code and set the switches and signals for the train.

The towers could take control when needed in emergencies.
Automatic Train Supervision (ATS) is the 21st Century version of IDENTRA.

Other systems that used it included
the Broad St. Subway in Philadelphia,
the Chicago Transit Authoritry
and the Toronto Transit Commission.


In addition both of these signals may further be GRADE TIME CONTROL, in that they will not turn yellow or green until the train has slowed to a pre-determined speed. there are two types.

Two Shot Timer:
The first (Y/S) is generally used on down grades where the train must be under a set speed for long length of track. As each signal clears to green, the next changes from red to Y/S.

One Shot Timer:
The second type is usually found at sharp curves, where once the train has slowed to the authorized speed, it may resume normal speed after leaving the curve.

Diagram showing how grade time signals work with the GT 20 sign in advance of the yellow over "S" signal. As the train slows to the designated speed, each signal clears and the next displays yellow over "S".

Station Time Signals:
Station Time signals allow a following train, under the designated speed limit, to enter a station as the leading train leaves. All ST sections are preceeded by a ST speed limit sign. Some station time signals display the speed at which the train may move. Without ST signals, the following train would have to wait outside the station until the leading train has left the station.

Diagram showing How Station Time Signals Work with a ST 10 sign in advance of a red over "10" signal.


All signals have a "TRIP STOP" which is in the raised or "TRIPPING" position when the signal is RED. If the train operator tries to pass the signal the TRIP STOP will open a air valve called the "TRIP COCK" on the subway car's TRUCK (the TRUCK is the part of the car which holds the motors and wheels). The top of the tripper and the trip cock are painted yellow so that if they are engaged, there will be telltale strikemarks.

The open valve causes the train brakes to apply in EMERGENCY. The train brakes cannot be released again for about 20 seconds giving the train operator time to think about what he/she did wrong.


Signals are said to have two atributes -


This is the color or combination of colors actually being displayed to the train operator.


This is the meaning of the signal to which the train operator must react.

To protect against malfunctioning signals displaying invalid or no aspects the RULE BOOK states that such signals are to be taken as its MOST restictive indication. That is, an automatic signal would be trated as a stop. An interlocking signal would be treated as a stop and stay.




Green Signal


Proceed with caution next signal is RED

The original IRT signals had the yellow aspect at the bottom and the red in the center

STOP radio for permission to pass

Grade time signal (Two Shot) - signal will turn green if train slows down next signal is RED. Usually used on a down grade for an extended length of track. These are sometimes called two shot timers, because there is alway a caution signal after the time signal that will clear to a timer if the train is under the speed limit.

Diagram showing how grade time signals work with the GT 20 sign in advance of the yellow over "S" signal. As the train slows to the designated speed, each signal clears and the next displays yellow over "S".

Grade time signal - signal will turn green if train slows down next signal is RED and the track switch is set for DIVERGING ROUTE.

Grade time signal (One Shot) - usually used for a sharp curve where the train may get back to normal speed after passing the curve. This is sometimes called a one shot timer because there is only one chance to get the train down to speed.


The top head usually denotes the condition of the track ahead and the bottom head tells what for which route the track switches are set. The switch routes are classed as MAIN or DIVERGING, however there is no consistancy as to which is which. The train operator must know what signal aspects to accept at each interlocking signal. Although I show the X L14 plate in red, the actual signs in use today are black on white. The white on red, used on the old IRT signals are more colorful though.
The original IRT interlocking signals were different in that each route controlled by a signal had its own head with G/R/Y (yes the IRT had the red in the middle) as needed. It was up to the train operator to kow which route was set up. A typical IRT signal might show R/R/Y meaning proceed with caution on the second diverging route. The PATH (former H&M) signals are similar. They are alway right hand route over the left hand route.



Proceed on MAIN ROUTE

Proceed with CAUTION on MAIN ROUTE

Time signal MAIN ROUTE

If a 'D' appears in place of the 'S', it is a time signal MAIN ROUTE and the next interlocking is set for DIVERGING ROUTE


Determining the MAIN or DIVERGING routes. It's not just which is straight and which turns off.


DeKalb Ave on the BMT was unique before the interlocking and station were rebuilt in the late 1950s as the first part of the Chrystie St connection. Track B-1 from the Montague St tunnel had the following aspects on the lower head:

Track Layout
Green - straight to the Brighton line
Yellow - right hand switch to the 4th Ave line
Blue - left hand switch to the by-pass track

From the 1944 rule book:
Proceed with caution, the next signal may be stop.


STOP AND STAY - call (radio or phone) for insructions if the signal does not clear after a few minutes.

STOP, push "CALL ON" button, look at track switch for proper route and proceed prepared to stop in half of your range of vision. Pushing the CALL ON button causes the TRIP STOP to move to the clear position allowing the train to move past it. Since the CALL ON signal is displayed by the tower operator and accepted by the train operator both are responsible for moving the train.


The original IRT used interlocking signals similar to mainline railroads. In places like Bowling Green, where there were two or more routes from the signal, each route had its own signal head that could display red yellow and sometimes green. The other heads displayed red aspects. It was up to the motorman to know which aspect was for each route.

Whichever head was NOT red would indicate which route was set up and whether the next signal was clear or stop.

Original H&M or PATH interlocking signals are similar to the original IRT, usually right had route over the left hand route. The H&M had provision for a second left had route.

Proceed - on the route indicated

The 1944 rule book does not include any example where the third route had a green aspect.

There were also signals that controlled four routes with an additional head with only red or yellow aspects. One might have been on the southbound Lexington local track north of Grand Central. There is a ladder track that crossed the two express tracks and had slip switches to enter GC on any of the four tracks.
Proceed with caution on the route indicated, the next signal may be stop.

At Bowling Green the signals were:
Top - Brooklyn
Middle - Inner loop
Bottom - Outer loop
Stop and Stay


TO Signal Clear WW

This is a Train Order Signal that is used to tell a train operator any special instructions, such as re-route, local to express switch, or wrong-rail through tunnel. The White lights mean there are no orders.

TO Signal Clear WW

This train order signal is telling the train operator to call 3111 for instructions. The telephone number is lighted as well as the red lights.


Added at the suggestion of John H.
Gap fillers are used 14th St - Union Sq and South Ferry . The Gap Fillers extend out from the platforms to bridge the space between the platform and the car body and door at the curved stations. When the train stops on the detector circuit, the Gap Fillers extend and signal aspect turns red and is a Stop and Stay indication. After the train begins to move, the operator may not pass the GF signal until the red light is extinguished and the GF light is lit. The number or letter under the GF represent the track designation. In the samples below it is the for Track A of the two track South Ferry Loop.
The South Ferry loop closed to regular passenger service on March 16, 2009, when the new station opened. See the Original station photos here.
Stop and Stay. The Gap Filler is extended.
Proceed, Gap Filler has retracted.


Wheel Detector signals were installed at interlockings in 1996. They are designed to further enforce the speed at which a train travels through an interlocking. Most are only active if the switch is set to the diverging route. The train must remain under the speed limit until the WD END sign is reached.
Sign at the start of the wheel detector section
Wheel detector off for your route. The switch is set for the main route.
Wheel detector on for your route and the train speed is within the speed limit
Wheel detector is active and the train is moving too fast. If the train doesn't slow down, the automatic stop arm will trip the train.
End of the wheel detection area

PATH Grade Time and Interlocking Signals

The PATH system operates subway style trains between 33rd St/6th Ave and the World Trade Center in Manhattan to Hoboken and Newark, NJ. The signals are similar to those on the subway with a few differences.

Grade time signals are yellow/yellow, with the second yellow in a single lens head.

On the original H&M and PATH interlocking signals the non RED aspect indicated right hand route over left hand route. Where there were three routes controlled by the same signal, it would have been for the R/M/L route.

Proceed on route indicated next signal is clear.

Proceed on route indicated next signal is caution or stop.

In addition, the non RED head might also display Y/Y signifying grade time control on that route.

Some locations have illuminated track or route indicators used in conjunction with the lower head clear or caution.
1,2,3 are track numbers at places like Hoboken and 33rd St
The letters are specific to each junction and have unique aspects for each.




At some interlockings, the route established is indicated by an illuminated Left or Right.


Hudson and Manhattan - PATH


COMMUNICATIONS BASED TRAIN CONTROL (CBTC) has been placed into service on the Canarsie L line in 2006 and is due on the Flushing line by 2016. This technology uses laser diode signals to 'tell' each train how far ahead the leading train is. This allows for more trains per hour to be operated on the line. It is the signal system of the next generation. Both the trackways and the cars need special equipment to make CBTC fully workable. However, non-CBTC cars may operate in CBTC territory since the original signal system has been integrated into the system.

When the wayside hardware detects a CBTC train, it compares the train speed to those in front and back and signals to each the locations and allowable speed to all trains. Wayside signals flash the green light while a CBTC train is operating and the system recognizes the trains.

When leaving CBTC areas, the interlocking signal will display the appropriate non-CBTC aspect for the exiting route. The train operator will then depend on wayside signals.

If the CBTC system on the train fails or the wayside equipment fails to detect the train the wayside signals revert to normal operation and control the railroad. If a non-CBTC train is on the line, the wayside signals control it and keep CBTC trains far enough behind it as if it were following the old signals.

Entering and leaving Communication Based Train Contol (CBTC) area.
Enter CBTC

When entering, the train operator must insure tha the wayside and in cab aspects agree. If they do not agree, the train is to be stopped and the control centerr must be contacted.

Enter CBTC

When leaving, the operator must insure that the cab aspects return to non-CBTC opeation.


This sign is a reminder that are trains are running automatically, track and signal employees must get permission to enter the tracks.

In trackway CBTC detector - Photo by Austin T. Edwards.

Here are some articles about CBTC

Status Report June 2004
Other projects from Transportation Systems Design, Inc.
Wikkipedia Article

Use this link to view the MTA Video Full Screen


A new technology for the 21st Century is Automatic Train Supervision (ATS) and is installed on the mainline parts of the IRT (lines 1-6). This is a system that uses a transponder that signals to interlockings the route for a train setting the swtiches and clearing the signals. This appears to be related to the IDENTRA system used in many systems (including the IRT Flushing line) in the 1950's. Readers embedded between the rails read the transponder and set the switches and signals as the trains approach interlocking junctions. Information about each train's progress is also transmitted to the central control office database.
In August 2008, this system failed causing chaos on the IRT. Before the subway was restored to normal, each train operator had to call control to report their train ID and location.


Starting lights - three green lights along the ceilings at terminals controled by the dispatcher to indicate to the conductor to close the doors for the train to depart the terminal. Some terminals have a bell sounding in addition to the lights.

In some terminals, the switch controlling the conductor starting lights in the dispatcher's, off also throws the track switch and sets the signal for that track.

Holding lights - three yellow lights along the ceilings at intermediate stations controlled by the dispatcher to indicate to the conductor to hold the doors open. Used to make trains wait for connections or scheduled departure time from stations.

Gap filler indicator - tells the conductor how many cars the gap filler system has detected. The doors must not be opened until the correct number of cars is displayed. Move mouse over the photograph to enlarge it. Click for full size photo in a new window.

Conductor indciation board - tells the conductor that the train is properly positioned in the station to safely open the doors.
There may be multiple boards for different length trains and types of equipment (R-40 vs R-143).

Depending the on the type of cars, the conductor may be located in various cars. All cars up until the R-38, the conductor could be located in any cab. In the R-40 and R-42, the conductor could only be located in the married or #2 end of each car. In the subsequent cars the conductor could only be located in the end units of the ABBA and ABBB'A sets.

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- Joseph D. Korman - The JoeKorNer