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Dan05979

Subway signals

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I was curiose to know how does a subway signal know a train has passed it, for example how does it know the entire set of cars has passed a green signal to let it turn red and then the brake trip arm lifts up? is it done by the weight of the train or magneticly? Any of you "buffs" know?

 

Same thing with a speed sensitive signal, how does it know if your going to fast? I think its the gt signal with the white light?

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I believe it's done by sensors, I could be wrong about that. You must be talking about the Grade Time Signal.

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Grade time signals work just like reagular signals, using electromechanical relays. A grade time signals or GT works by knowing how long it takes for a train traveling at a certian speed to go from known point A to known point B, When a train enters the signal block, the timer starts to count down. If a train is traveling at or lower then the posted speed, the signals will clear. If the train is traveling at or faster then the posted speed, the signal will not clear. Yes I did just say a signal may not clear when a train approches at the posted speed since some signals are not calibrated correctly. Now depending on the type of GT signal, the train may be tripped or it may not be.

A "One Shot" GT:

appr03.jpg

These signals usually clear at very low speeds like 5 or 10 MPH and are usually found around very sharp curves.

A "Two Shot GT":

appr07.jpg

The red signal AFTER a yellow signal with an ILLUMINATED "S" is the timed signal. "Two Shot" means that you have a second chance to adgust your speed should you pass the yellow signal with the illuminated "S" before it changes. These signals are usually used near slight curves or on straight sections of track where excess speed is not needed.

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So that one shot signal is almost like playing a game you get one chance if you fail you die.

 

What about my other question?

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So that one shot signal is almost like playing a game you get one chance if you fail you die.

 

What about my other question?

 

Kinda, you fail a one shot and you get tripped, hitting a timer is a big deal. As for the first part, I'm working one that and I should have something up by tonight if no one else gets to it first.

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The signal tracking system for the subway and most rail networks operates by sending a current through the rails, the axle/wheel sets close the circuit, telling the system where the train is, how long it is etc. Signal cables are festered all over switch areas, and at regular intervals along the track otherwise. The speedo signals i'm not sure bout, but i believe some kinda signal may be sent from the speed control system on the train thru the wheels.

 

 

Tripcocks at the signal control points (the end of the relevant block in the direction of travel) activate the onboard emergency brake i they go past a red signal. The trip cocks raising to "protect" position is the noise you hear after a train has left a station. If a train is lost track of, the line immediately goes red, how much of the line is specific to that stretch of track.

 

On a proper railroad you have cab signaling that trips the brakes if the engineer doesn't respond to a red after 6 seconds.

 

- A

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The signal tracking system for the subway and most rail networks operates by sending a current through the rails, the axle/wheel sets close the circuit, telling the system where the train is, how long it is etc. Signal cables are festered all over switch areas, and at regular intervals along the track otherwise. The speed signals i'm not sure bout, but i believe some kinda signal may be sent from the speed control system on the train thru the wheels.

There are no signals sent from the train to the rails on any NYCT trains even the (L) line CBTC trains. What your talking about is "cab signaling" which is not in use on any line.

 

Tripcocks at the signal control points (the end of the relevant block in the direction of travel) activate the on board emergency brake i they go past a red signal. The trip cocks raising to "protect" position is the noise you hear after a train has left a station. If a train is lost track of, the line immediately goes red, how much of the line is specific to that stretch of track.

The "trip cock" (Car Born Tripping Device) is the part that is on the car. The device on the ground is the "Trip Arm". Now what is this "lost or track" you talk about?

On a proper railroad you have cab signaling that trips the brakes if the engineer doesn't respond to a red after 6 seconds.

Proper railroad? NYCT is not a railroad, it is a rapid transit system.

 

- A

Replied in red.

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by the stop arm is a insulated joint...once the last set of wheels come off of that insulated joint the stop arm comes up.......keep in mind though in some instances, you can do what as known as "key by" a red signal(in some terminals, on storage tracks,etc).........

 

pretty much ind awnsered the other question; the only bad thing about the 2 shot timer; if you dont let it clear in front of you, the next signal you pretty much have to stop the train in order for the next signal to clear............

Edited by rtype3995
left out a word in my sentence

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by the stop arm is a insulated joint...once the last set of wheels come off of that insulated joint the stop arm comes up.......keep in mind though in some instances, you can do what as known as "key by" a red signal(in some terminals, on storage tracks,etc).........

 

 

All signals can be "keyed by" except Homeballs and signals that have had the key by feature removed, but those signals are marked with a "No Key By" sign. If a Home Ball displays red over red, but a train needs to pass that signal. A "Call On" will be given which is an amber light at the very bottom. When that happens, the T/O must come up close to the signal and activate the stop arm release then proceed at restricted speed and extrema caution expecting to find a train ahead or a broken rail. To pass a "No Key By" signal at danger, the stop arm must be stepped on and the T/O must ensure theat the arm is retained. Many signals have a 10 second timer before the arm goes down and stays down. If the T/O is not careful, the trip arm could pop up and trip the train. Of course all of this is done with permission from RCC or the local tower.

Edited by INDman
  • Upvote 1

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Doesn't have to be hooked down unless it is malfunctioning. It only needs to be stepped on, and then it should retain.

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Doesn't have to be hooked down unless it is malfunctioning. It only needs to be stepped on, and then it should retain.

 

Upon looking at my books, that's right. Just about every time I have heard RCC tell a train to key by a "no key by" signal I have heard them tell the T/O to hook the arm down since I have only heard them do this when there are major signal problems.

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Upon looking at my books, that's right. Just about every time I have heard RCC tell a train to key by a "no key by" signal I have heard them tell the T/O to hook the arm down since I have only heard them do this when there are major signal problems.

 

Does this happen often? I remember when they started putting those wheel detector signals right after the 14th street disaster on the (4) line.

 

 

Also, why on the IRT line the brake trips are on the right and on the left on every other line.

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Does this happen often? I remember when they started putting those wheel detector signals right after the 14th street disaster on the (4) line.

 

 

Also, why on the IRT line the brake trips are on the right and on the left on every other line.

 

When ever it snows, it really messes with the signals and they won't clear. As for WDs, I have not seen any new ones go in and it seems like the TA likes GT signals better.

As for the location of the trips, I have no idea but I'll ask around. That's a question I had never thought of.

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Each signal governs a "bloc" behind it (a section of track) and as the trains enters the signal goes red. The stop arm doesnt come up until the train leaves the bloc and it knows that because the tracks contain electrical circuits so essentially each bloc is a track circuit. the stop motor is de energized after the train leaves and the stop arm comes up. the signal doesnt clear until the train has left the second bloc ahead of it.

 

 

A Grade time is when u have a descending area where the train could pick up too much speed so the relay has a timer on it which was determined as a safe velocity for the train so if the train is moving too quickly the TO has 2 chances to bring the speed down if he moves too quickly he will get to the signal before the timer runs out and the signal wont clear essentially tripping the train.

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Each block is a separate track circuit. When a train crosses from one signal block to the next, the train wheels bridge an IJ (insulated joint) which creates a clever short circuit that identifies the train as occupying the next block.

 

Track circuits use alternating current so 600V DC or any other DC for that matter won't affect their ability to work properly.

 

Any time a train is present on a block the signals that protect the blocks behind it will turn red. The stop arms retain until the train has left the previous block. This prevents a train from getting trip by a red signal which is there to protect it (aka its own red).

 

Timers (aka grade time signals) begin counting down from the moment a train enters a block. Timers are not calibrated to detect speed, only time.

 

One shot timers protect the NEXT block. The timer is set by mathematically figuring out how long a train takes to get from point A to point B. Naturally, the timer is at point B and displays red. As soon as the train reaches the signal at Point A (by bridging an IJ), the timer at point B begins counting down. When the counter runs out, the Point B signal clears to yellow or green. If the train is going too fast, it will arrive at Point B before the timer has run off and the signal will still be red, putting the train in emergency. If it is going the proper speed, the signal will clear before the train arrives, and the stop arm will go down and retain, allowing the train to pass.

 

Two shot timers protect TWO blocks ahead. The timer is set by mathematically figuring out how long a train takes to get from point A to point B. However, the timer is at point C (beyond point :(. As soon as the train reaches the signal at Point A (by bridging an IJ), the timer at point C begins counting down. The signal at point B functions as an automatic that precedes signal C. When signal C is red, Signal B is yellow. The timer at Signal C is set to clear in the time it should take the train to go from Point A to Point B. When the counter runs out, the Point C signal clears to yellow or green, and the point B signal clears to green. If the train is going too fast, it will arrive at Signal B before the Signal C timer has run off and the signal will still be yellow, warning the train operator that he is going too fast, and that Signal C is still at danger (but not putting the train in emergency). If it is going the proper speed, Signal B will clear to green and Signal C to yellow or green before the train arrives, allowing the train to continue and letting the operator know his speed is OK. With a string of two shot timers, if the operator continues excessive speed, he will eventually hit a red signal and his train will be tripped because he will get progressively closer to the signal which is functioning as "Signal C" in that particular instance.

 

Therefore one shot timers are much more restrictive than two shot timers. Some timers are conditional. For instance, some timers only apply when a diverging route is set for a switch at a home signal (ie train is taking the turnout at the switch so it must go slower than if it's going straight). Then there are...

 

Station time signals are conditional grade time signals that apply more restrictive "speed limits" (aka their countdown timers are longer) to a following train, but only are active if there is a train nearby in front. They exist to allow trains to close in on their leaders provided the following train demonstrates that it is doing a safe speed. Doing so is desirable as it allows trains to keep moving and keeps delays from happening further back down the line.

 

Wheel detectors measure speed instead of time. They detect the rate at which individual axles bridge the IJ (calculated based on allowable speed), and if the rate is excessive, a stop arm is raised at the wheel detector, tripping the train. If the train is doing the proper speed, stop arms stay down. The train will receive an idea that it has passed the wheel detector when a yellow sign in the tunnel displaying "WD END" is passed.

 

Every signal will turn red if a train passes it, but only some signals have Grade Time, Station Time, or Wheel Detector components to them. Some timers are conditional and only turn on in certain cases. Same is true of wheel detectors. Also - very important - Signals will always display the MOST RESTRICTIVE aspect. For instance, if a timer is active and has run out, but there is a train in front of it, even though the timer has run out, the signal will stay red. This is a safety feature that makes signalling as safe as possible. It's also why one shot timers are so restrictive. A T/O can't just fly up to them assuming they'll clear the way they usually do. Always leave space to stop because the signal may not only be red because of a timer, there may also be a train in front in which case it won't clear and he'll hit the signal.

 

Likewise, when signals malfunction, they default to red. Prevents collisions (because a false green with a train in front is worse than a false red with no train in front). If a signal is red for no apparent reason, that's when procedures like what IND described will happen ("key by") and you'll hear about a "signal problem" - usually means one of the signal relays has gone bad

Edited by SubwayGuy
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To further things, the one-shot timers are actually red with a lunar white below it. That is actually a clear signal (albeit on time). when there's no white below it, its basically a regular automatic. the two shots have a yellow with a 'S' below it (a red behind it), and a yellow with a 'D' signals a diverge is ahead at the next home signal.

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Each block is a separate track circuit. When a train crosses from one signal block to the next, the train wheels bridge an IJ (insulated joint) which creates a clever short circuit that identifies the train as occupying the next block.Track circuits use alternating current so 600V DC or any other DC for that matter won't affect their ability to work properly.Any time a train is present on a block the signals that protect the blocks behind it will turn red. The stop arms retain until the train has left the previous block. This prevents a train from getting trip by a red signal which is there to protect it (aka its own red).Timers (aka grade time signals) begin counting down from the moment a train enters a block. Timers are not calibrated to detect speed, only time.One shot timers protect the NEXT block. The timer is set by mathematically figuring out how long a train takes to get from point A to point B. Naturally, the timer is at point B and displays red. As soon as the train reaches the signal at Point A (by bridging an IJ), the timer at point B begins counting down. When the counter runs out, the Point B signal clears to yellow or green. If the train is going too fast, it will arrive at Point B before the timer has run off and the signal will still be red, putting the train in emergency. If it is going the proper speed, the signal will clear before the train arrives, and the stop arm will go down and retain, allowing the train to pass.Two shot timers protect TWO blocks ahead. The timer is set by mathematically figuring out how long a train takes to get from point A to point B. However, the timer is at point C (beyond point cool.png. As soon as the train reaches the signal at Point A (by bridging an IJ), the timer at point C begins counting down. The signal at point B functions as an automatic that precedes signal C. When signal C is red, Signal B is yellow. The timer at Signal C is set to clear in the time it should take the train to go from Point A to Point B. When the counter runs out, the Point C signal clears to yellow or green, and the point B signal clears to green. If the train is going too fast, it will arrive at Signal B before the Signal C timer has run off and the signal will still be yellow, warning the train operator that he is going too fast, and that Signal C is still at danger (but not putting the train in emergency). If it is going the proper speed, Signal B will clear to green and Signal C to yellow or green before the train arrives, allowing the train to continue and letting the operator know his speed is OK. With a string of two shot timers, if the operator continues excessive speed, he will eventually hit a red signal and his train will be tripped because he will get progressively closer to the signal which is functioning as "Signal C" in that particular instance.Therefore one shot timers are much more restrictive than two shot timers. Some timers are conditional. For instance, some timers only apply when a diverging route is set for a switch at a home signal (ie train is taking the turnout at the switch so it must go slower than if it's going straight). Then there are...Station time signals are conditional grade time signals that apply more restrictive "speed limits" (aka their countdown timers are longer) to a following train, but only are active if there is a train nearby in front. They exist to allow trains to close in on their leaders provided the following train demonstrates that it is doing a safe speed. Doing so is desirable as it allows trains to keep moving and keeps delays from happening further back down the line.Wheel detectors measure speed instead of time. They detect the rate at which individual axles bridge the IJ (calculated based on allowable speed), and if the rate is excessive, a stop arm is raised at the wheel detector, tripping the train. If the train is doing the proper speed, stop arms stay down. The train will receive an idea that it has passed the wheel detector when a yellow sign in the tunnel displaying "WD END" is passed.Every signal will turn red if a train passes it, but only some signals have Grade Time, Station Time, or Wheel Detector components to them. Some timers are conditional and only turn on in certain cases. Same is true of wheel detectors. Also - very important - Signals will always display the MOST RESTRICTIVE aspect. For instance, if a timer is active and has run out, but there is a train in front of it, even though the timer has run out, the signal will stay red. This is a safety feature that makes signalling as safe as possible. It's also why one shot timers are so restrictive. A T/O can't just fly up to them assuming they'll clear the way they usually do. Always leave space to stop because the signal may not only be red because of a timer, there may also be a train in front in which case it won't clear and he'll hit the signal.Likewise, when signals malfunction, they default to red. Prevents collisions (because a false green with a train in front is worse than a false red with no train in front). If a signal is red for no apparent reason, that's when procedures like what IND described will happen ("key by") and you'll hear about a "signal problem" - usually means one of the signal relays has gone bad

This cleared up so much confusion I had!! Thank you for this!!

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I mean it is a nice explanation of the signal system, but this thread is still 6 years old...

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I mean it is a nice explanation of the signal system, but this thread is still 6 years old...

You're right. As informative as this is, it's still necroposting, especially with no need information posted in it.

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