What is a signal block and how long is one :?:
signal block
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jmp883
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A very good question. I'll try to answer it as best as I can. I'm a former New Jersey Transit train dispatcher, but still a railfan. Anyone who has more expertise, please update this post, correct it, or let me know I basically got it right.
A block is not a set length. It varies from railroad to railroad and is dependent upon many factors. Very very simply, block length is determined by train frequency and average train length for that territory. On NJT the majority of blocks were rather short, only a mile or two long and all normal train movements were controlled by Automatic Block Signals (ABS) via Centralized Train Control (CTC). By the way, ABS block signals not only indicate track occupancy, they also indicate train speed.
Now I know you only asked about block length but let me enlighten you to how block length and signaling all fit together.
CTC is a form of train control where a dispatcher controls all signals and interlockings from a remote location. On an ABS/CTC system there is a low-current voltage passed through the rails that controls the signal system. When a locomotive, freight, or passenger car completes the circuit by entering a block it will then display an appropriate signal, not only for that block, but usually for the next block ahead as well. An advantage to this system is that you can have numerous trains running in the same direction, or opposing, at the same time (as NJT does) and yet you can keep them safely spaced. ABS/CTC will know that there are trains on the railroad, what blocks they are in, and will post the appropriate signals to following trains that will indicate to the train crews what speed to follow. Interlocking signals are controlled by the dispatcher and indicate speed and routing through an interlocking plant. These specific details are spelled out in employee timetables along with all the different signal aspects. ABS signals are those with a numberplate (actually it's milepost location). Interlocking signals have no numberplates and are controlled by the dispatcher.
ABS signals can be either continously lit or approach-lit. On NJT they were approach-lit, meaning they were dark until the train was usually two blocks away. Approach-lit signals save on bulb life. They can also help the railfan....if you see an automatic light up you know a train is approaching. If you see all reds the train will be coming from behind the signal you're looking at. If you see any combination of red, yellow, or green the train will be approaching that signal. Once the train is one or two blocks past the signal you're at, the ABS signals will go dark until the next movement. Interlocking signals light up only when the dispatcher sets a route through the interlocking. They also go dark after the train passes.
I hope this answered your question...somewhat. As I stated at the start of the post if anyone with signal experience can add to, or correct anything in my post, I'd greatly appreciate it.
A block is not a set length. It varies from railroad to railroad and is dependent upon many factors. Very very simply, block length is determined by train frequency and average train length for that territory. On NJT the majority of blocks were rather short, only a mile or two long and all normal train movements were controlled by Automatic Block Signals (ABS) via Centralized Train Control (CTC). By the way, ABS block signals not only indicate track occupancy, they also indicate train speed.
Now I know you only asked about block length but let me enlighten you to how block length and signaling all fit together.
CTC is a form of train control where a dispatcher controls all signals and interlockings from a remote location. On an ABS/CTC system there is a low-current voltage passed through the rails that controls the signal system. When a locomotive, freight, or passenger car completes the circuit by entering a block it will then display an appropriate signal, not only for that block, but usually for the next block ahead as well. An advantage to this system is that you can have numerous trains running in the same direction, or opposing, at the same time (as NJT does) and yet you can keep them safely spaced. ABS/CTC will know that there are trains on the railroad, what blocks they are in, and will post the appropriate signals to following trains that will indicate to the train crews what speed to follow. Interlocking signals are controlled by the dispatcher and indicate speed and routing through an interlocking plant. These specific details are spelled out in employee timetables along with all the different signal aspects. ABS signals are those with a numberplate (actually it's milepost location). Interlocking signals have no numberplates and are controlled by the dispatcher.
ABS signals can be either continously lit or approach-lit. On NJT they were approach-lit, meaning they were dark until the train was usually two blocks away. Approach-lit signals save on bulb life. They can also help the railfan....if you see an automatic light up you know a train is approaching. If you see all reds the train will be coming from behind the signal you're looking at. If you see any combination of red, yellow, or green the train will be approaching that signal. Once the train is one or two blocks past the signal you're at, the ABS signals will go dark until the next movement. Interlocking signals light up only when the dispatcher sets a route through the interlocking. They also go dark after the train passes.
I hope this answered your question...somewhat. As I stated at the start of the post if anyone with signal experience can add to, or correct anything in my post, I'd greatly appreciate it.
GREAT info. Just moved to a different state, and I have a busy freight trail line out just past my backyard. Great to hear it from a dispatcher. 8)
erikTromatowski
Member
Yea, that is correct. Even though signal system specifics can differ upon railroad, thats pretty much how it all works. For example, on the NEC, signals are continuosly lit. Signals used to all be of amber color, but had various positions, each position meaning something different (PRRs system). Amtrak though, is currently, and possibly completely has, replaced these signals. They are still of the same style, just, display various colors. Also, I belive there is a 1 or 3 block seperation on the NEC, however you want to put it (one block away, signals are stop, 2 blocks away, signals are restricting, and 3 blocks away signals are approch. Or something like that...). As I said though, good job on explaining the signals, even cleared up some things to this life long railfan, and 15 year old whos lived in the shadow of the NEC all his 15 years as well.
Starion
Member
Are we talking about block signals and automated train controls? I think I have a few links about them.
Sometimes I here absolute block and permissive block to "a platform or a signal" on my scanner.
The amount of technology needed in modern railways is amazing. I hear about interlockings, cranking signals, blocking signals and other things I can't remember.
The track circuits about 25 miles from me keep dying though.
One circuit a few miles from my house died too.
Sometimes I here absolute block and permissive block to "a platform or a signal" on my scanner.
The amount of technology needed in modern railways is amazing. I hear about interlockings, cranking signals, blocking signals and other things I can't remember.
The track circuits about 25 miles from me keep dying though.
One circuit a few miles from my house died too.
at least here on the up out of kc the signals are like this stop(red), approch(hard yellow), advance approch(flashing yellow) and clear(green). restricted can be displayed as luner, flashing red. but u normaly dont see restricted running in normal blocks comming up behind another train. hope that helps a little
Is this the reason for the little silver shacks near some if not all train crossings?
I also would add that the lights only work providing the engineer is not a sleep. :shock:
With this said anyone know if they are changing the way this warning system works? So to alert a sleeping engineer.
Is Engineer the correct term?
Forgive my stupidity but can't understand.
I also would add that the lights only work providing the engineer is not a sleep. :shock:
With this said anyone know if they are changing the way this warning system works? So to alert a sleeping engineer.
Is Engineer the correct term?
Do you mean you have heard them say this? Or have you some how taped a circuit?Starion said:The track circuits about 25 miles from me keep dying though.
Forgive my stupidity but can't understand.
the shacks near the crossings are the control boxes for the crossing gates and lights, u should see a white light on the outside of the shacks when a train is comming, that means that the crossing device is working. The silver shacks are also near control points. as for your second point we the train crew are both in charge of following the siginals aka the conductor and engineer. most locomotives have whats called alerters on them, after 30 sec or so of no control movement they start to sound an alarm and then after another 30 sec or so if nothing is moved on the control stand it will stop the train. i hope u all can understand me tonight i just got home from another run and have been up for 30 hours so i am a little tired and hopefully i have explained it well enough
JamesO
Member
The Alerter is also known as a "Dead Man"
Older trains had a pedal that the Engineer needed to use his foot to push, kind of like a gas pedal. Problem was the circuit was very basic and some train Engineers would put a tool box or some other heavy object on the pedal so they could wander about the cab of the train while it was in motion. Not good practice.
Newer trains have a "Dead Man" that cannot be spoofed. The Alerter needs constant feedback when they time out. It typically looks like a 3-5" long spring handle that the Engineer needs to bat every so often when the countdown timer expires. It is typically located near the throttle on the engine control console. I think they have a rather random timer sequence to keep these newer Alerters from being spoofed and the Engineer "Alert".
JamesO
Older trains had a pedal that the Engineer needed to use his foot to push, kind of like a gas pedal. Problem was the circuit was very basic and some train Engineers would put a tool box or some other heavy object on the pedal so they could wander about the cab of the train while it was in motion. Not good practice.
Newer trains have a "Dead Man" that cannot be spoofed. The Alerter needs constant feedback when they time out. It typically looks like a 3-5" long spring handle that the Engineer needs to bat every so often when the countdown timer expires. It is typically located near the throttle on the engine control console. I think they have a rather random timer sequence to keep these newer Alerters from being spoofed and the Engineer "Alert".
JamesO
those springs or what ns and older csx used to have most of what union pacific has is a button to push. most of those springs came form when they retrofited older locos with alerters along with the spings they would install a red light bulb on top of the stand. the ones we have give u 30 sec to push or move somthing before they set the brakes.
wbigcount said:
Sounds like that would get aggravating in a very short time! :x
cohenner5377
Member
Dead Man & Signals
The "dead man" device will, as the previous post suggests, sound a loud whoop or beeping if there has been no activity on the throttles or brakes in over 30 seconds. It then gives 15 seconds (I think) for the cengineer to acknowledge the signal (but ptessing a button), before it activates the air brakes and brings the train to an emergency stop.
Additionally, it has been suggested to me by a MARC conductor (Penn Line running on the NEC) that if the engineer should fall off his seat (as having suffered a heart attack or other malady), the train will stop immediately as well.
This all fits in with the signal system, because the signal system also has the capability to stop the train. If the engineer goes through the block, and he has a stop signal, the train will additionally stop.
It should also be pointed out that the signal system on the NEC and on CSX's system are totally different. A number of commuter lines run on both CSX & Amtrak controlled tracks (for instance, the MARC Camden line starts on CSX trackage in Baltimore and ends up on Amtrak trackage in Washington).
The "dead man" device will, as the previous post suggests, sound a loud whoop or beeping if there has been no activity on the throttles or brakes in over 30 seconds. It then gives 15 seconds (I think) for the cengineer to acknowledge the signal (but ptessing a button), before it activates the air brakes and brings the train to an emergency stop.
Additionally, it has been suggested to me by a MARC conductor (Penn Line running on the NEC) that if the engineer should fall off his seat (as having suffered a heart attack or other malady), the train will stop immediately as well.
This all fits in with the signal system, because the signal system also has the capability to stop the train. If the engineer goes through the block, and he has a stop signal, the train will additionally stop.
It should also be pointed out that the signal system on the NEC and on CSX's system are totally different. A number of commuter lines run on both CSX & Amtrak controlled tracks (for instance, the MARC Camden line starts on CSX trackage in Baltimore and ends up on Amtrak trackage in Washington).
Yes some nights it gets real old real quick, at least here on the bn and up (i work for up) u can get out of your seat as much as u want it wont stop the train or do anything as long as i hit the alerter when the Engineer gets up to pee or somthing were fine but it has nothing to do with the seat. now there used to be a dead mans pedal on the floor many years ago but most of them are not around anymore, thats where most people get the dead mans name from but there called alerters. as for going by a signal and it stoping a train that is called postive train control, we do not have it on the up nor does the bn or ns have it here. and yes it is 30 sec before the alerter will stop the train with a full service braking not an emergency stop. also we use cab siginals in some parts and they too will stop a train in full service if you dont acknowledge them with in 30 sec but not emergency only full service. as for both it is called a penalty brake application.
Starion
Member
From what I can tell by listening, a signal block is in between signals or train platforms. So, the length of a block can vary.
jmp883 explained the signal block very well. My hats are off to him.
jmp883 explained the signal block very well. My hats are off to him.
Hi guys,
Just to add to what the dispatcher said, here's how it works on an electrified system using the NEC and NJT as an example. FYI, NEC being ex-PRR and it's antique power system, otherwise NJT and it's modern one. The PRR used 25Hz 11KV catenary and the other lines in NJ used 60Hz 25KV, NJT's Coast Line being newly electrified uses the same. The new locomotives employ power inverters and aren't picky of what they eat unlike the old transformers that would burn out at the wrong voltage and frequency.
At the signal bridge you can see a big, low metal box between the rails connected to them by heavy cables each side of an insulating spacer and another connected to a grounding stake you probably can't see. This is the impedance bond, a frequency selective network. It separates the signal current usually 400Hz from the traction current which it sends to ground completing the circuit the locomotive draws power from. Somewhere in all this there are wires connected to the signal equipment box, but much of the wiring is buried under the RoW in a conduit out of sight.
In any case, you'll always find those insulating spacers at signal points, welded rail really isn't a continuous ribbon after all.
FYI, in Northern Ireland the IRA took advantage at one time of the characteristics of the system and used the rails as a telephone circuit. Yup, they'd connect modified Army field phones to the rails, pass the secret messages and fade into the woodwork once again.
Just to add to what the dispatcher said, here's how it works on an electrified system using the NEC and NJT as an example. FYI, NEC being ex-PRR and it's antique power system, otherwise NJT and it's modern one. The PRR used 25Hz 11KV catenary and the other lines in NJ used 60Hz 25KV, NJT's Coast Line being newly electrified uses the same. The new locomotives employ power inverters and aren't picky of what they eat unlike the old transformers that would burn out at the wrong voltage and frequency.
At the signal bridge you can see a big, low metal box between the rails connected to them by heavy cables each side of an insulating spacer and another connected to a grounding stake you probably can't see. This is the impedance bond, a frequency selective network. It separates the signal current usually 400Hz from the traction current which it sends to ground completing the circuit the locomotive draws power from. Somewhere in all this there are wires connected to the signal equipment box, but much of the wiring is buried under the RoW in a conduit out of sight.
In any case, you'll always find those insulating spacers at signal points, welded rail really isn't a continuous ribbon after all.
FYI, in Northern Ireland the IRA took advantage at one time of the characteristics of the system and used the rails as a telephone circuit. Yup, they'd connect modified Army field phones to the rails, pass the secret messages and fade into the woodwork once again.
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