How Do Amtrak's Cab Signals and ACSES Work?

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MattW

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Railworks just [finally] released the Northeast Corridor for Railworks2(3) which so far only includes an AEM-7 and Amfleets, but there's been some consternation within the various communities over just how exactly the in-cab signaling is supposed to work vs. how it really works in real life. The Railworks NEC includes a signal aspect PDF, and the AEM-7 manual indicates that the upper part displays the color-position-light signal aspect (no question there) while the lower part has two speeds: upper displaying signal speed, lower displaying track speed. The big question floating about this part is what defines track speed? The best example is the curve at Frankford Junction. On my first trip through, track speed was indicated as being 110mph, but track speed is only 55mph. I only discovered this after my Northeast Regional tipped over. What speeds does ACSES provide to the cab signals? Are things such as temporary speed restrictions supposed to be included? Also, how is an engineer supposed to know upcoming track speed such as the Elizabeth S-curve (ok, everyone should know this one by heart, but work with me here)? In-game, speed limit changes happen instantly, and there are no line-side speed limit signs warning of an upcoming reduction. Is this how it works in real life?

The next question is about signal speed. In normal railroad signals, I understand that if you get some sort of restricting aspect, you're supposed to pass the next signal at say 30mph and you have the entire block to slow down, so in theory, you could run maximum allowed speed right to the last second, then cut in full service braking and pass the signal at exactly 30mph. In-game however, any signaling speed changes require you to apply full service braking within a few seconds or it will apply the brakes (though not emergency brakes) if you've activated speed control. On the real NEC, are signal-speed changes regarded as immediate reductions, or is the speed reduction only required to be in force once the train has passed the signal?
 
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Acela150

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110MPH on the Frankford Junction curve!!! :unsure: :blink: GET OUT OF HERE!!! :lol: :unsure: I railfan there frequently.. I know how slow those trains go. :giggle: Great spot for sunlight BTW. I've heard a decent amount about this game.

As for the speeds most engineers I would imagine have each curve interlocking and what not memorized. I believe the S curve is 65. Not sure. Just a guess. The curve following Frankford Junction I believe is somewhere around 60 or 65. But I do agree that it should be posted if it's not.
 

jis

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110MPH on the Frankford Junction curve!!!
GET OUT OF HERE!!!
I railfan there frequently.. I know how slow those trains go.
Great spot for sunlight BTW. I've heard a decent amount about this game.

As for the speeds most engineers I would imagine have each curve interlocking and what not memorized. I believe the S curve is 65. Not sure. Just a guess. The curve following Frankford Junction I believe is somewhere around 60 or 65. But I do agree that it should be posted if it's not.
The story goes that the only reason any speed limit is posted on trackside signs on the NEC is a result of a strike by Operating staff many moons ago. Management decided to try to run the railroad by inducting people who had scant experience - clearly before the days of strict FRA regulations. In order to help them out the speed limits were posted to remind them. Operating crew, Engineers and Conductors, have route qualification and that together with employee TT carries all the info they need. In addition cab signal enforces most of the really critical speed limits anyway, even in the absence of ACSES(1). For example, that is why you get an approach medium approaching the Elizabeth S curve on the real railroad. I have no clue what they do in games. So normally those few posted signs are not really used and are also invalid for Acelas in many cases.

To answer to the original question regarding track speed (known technically as Civil Speed), in ACSES, the Civil speed is defined as the lowest of the PSR(2)s picked up from transponders and TSR(3) fed to the train by radio link or transponders, and the MAS(4) for the train class. The last bit is incidentally also received as part of the PSR and TSR message anyway. The message contains speed info for 5 different train classes. This computed (Civil) speed is the speed at which the train is allowed to operate on the segment of track irrespective of the possibly more liberal or conservative Cab Signal speed, and is displayed in the Civil Speed display on the ADU(5). Note that PSR delivered from Transponder does not necessarily apply to the entire section. The transponder message contains information about what sub section the PSR applies to and the train ATC computer displays the right speed for each point of the track as the train proceeds down the track. The actual speed at which the train is allowed to operate is the lesser of the Cab speed and the Civil speed at any point.

With the addition of ACSES, PSRs can be enforced more stringently using ACSES transponders, since Civil speeds can be specified with greater precision than via signal codes. In addition even TSRs can be transmitted using the ACSES radio link to feed those into the train ATC(6) computer. All that information is used to display the two speeds on the display. If ACSES is inoperative but CCTC(7) Cab Signal is operative, only the signal speed is displayed and the track speed should remain blank, and max speed is restricted to 125mph. If CCTC cab signal is also inoperative then speed is restricted to 79mph, and additional dispatcher clearance is required if cab signal equipment has failed just on the train.

1. ACSES - Advanced Civil Speed Enforcement System
2. PSR - Permanent Speed Restriction
3. TSR - Temporary Speed Restriction
4. MAS - Maximum Allowed Speed
5. ADU - Advanced Display Unit
6. ATC - Automatic Train Control
7. CCTC - Continuous Coded Track Circuit

BTW, on the real railroad ACSES is not yet turned on between Fair and Philly AFAIK. It will be turned on within the next several years. They have been installing the transponders for the last month or so.


The next question is about signal speed. In normal railroad signals, I understand that if you get some sort of restricting aspect, you're supposed to pass the next signal at say 30mph and you have the entire block to slow down, so in theory, you could run maximum allowed speed right to the last second, then cut in full service braking and pass the signal at exactly 30mph. In-game however, any signaling speed changes require you to apply full service braking within a few seconds or it will apply the brakes (though not emergency brakes) if you've activated speed control. On the real NEC, are signal-speed changes regarded as immediate reductions, or is the speed reduction only required to be in force once the train has passed the signal?
That is because the cab signal does not show the state of the signal that you are facing ahead of you (i.e. the next signal), but it shows what the state of the signal that you passed last would be if you were not occupying the block (i.e. what is the state of the signal that is ruling the current block). So any change in cab signal has to be acted on immediately. A cab signal is not a track side signal. This is so because the NEC cab signal system does not provide distance to next signal, so from the perspective of automatic train control it is useless to know what the state of the next signal is, since the computer does not know how far away it is. The exception to this is if the next signal is red in which case the cab signal transitions to restricting (no code) at some point ahead of the next signal.

Another difference BTW between just classic CCTC Cab Signal and that with ACSES overlay is, absent ACSES, Cab Signal will allow you to pass a stop signal at restricted speed, but ACSES will enforce a stop at a home signal that is indicating stop. Again, this is on the real railroad. I have no idea what the game does.
 
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amtrakwolverine

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110MPH on the Frankford Junction curve!!! :unsure: :blink: GET OUT OF HERE!!! :lol: :unsure: I railfan there frequently.. I know how slow those trains go. :giggle: Great spot for sunlight BTW. I've heard a decent amount about this game.

As for the speeds most engineers I would imagine have each curve interlocking and what not memorized. I believe the S curve is 65. Not sure. Just a guess. The curve following Frankford Junction I believe is somewhere around 60 or 65. But I do agree that it should be posted if it's not.
The story goes that the only reason any speed limit is posted on trackside signs on the NEC is a result of a strike by Operating staff many moons ago. Management decided to try to run the railroad by inducting people who had scant experience - clearly before the days of strict FRA regulations. In order to help them out the speed limits were posted to remind them. Operating crew, Engineers and Conductors, have route qualification and that together with employee TT carries all the info they need. In addition cab signal enforces most of the really critical speed limits anyway, even in the absence of ACSES(1). For example, that is why you get an approach medium approaching the Elizabeth S curve on the real railroad. I have no clue what they do in games. So normally those few posted signs are not really used and are also invalid for Acelas in many cases.

To answer to the original question regarding track speed (known technically as Civil Speed), in ACSES, the Civil speed is defined as the lowest of the Cab Signal Speed, PSR(2)s picked up from transponders and TSR(3) fed to the train by radio link or transponders, and the MAS(4) for the train class. The last bit is usually specified also as part of the PSR and TSR message anyway. The message contains speed info for 5 different train classes. This computed (Civil) speed is the speed at which the train is allowed to operate on the segment of track irrespective of the possibly more liberal Cab Signal speed, and is displayed in the Civil Speed display on the ADU(5). Note that PSR delivered from Transponder does not necessarily apply to the entire section. The transponder message contains information about what sub section the PSR applies to and the train ATC computer displays the right speed for each point of the track as the train proceeds down the track.

With the addition of ACSES, PSRs can be enforced more stringently using ACSES transponders, since Civil speeds can be specified with greater precision than via signal codes. In addition even TSRs can be transmitted using the ACSES radio link to feed those into the train ATC(6) computer. All that information is used to display the two speeds on the display. If ACSES is inoperative but CCTC(7) Cab Signal is operative, only the signal speed is displayed and the track speed should remain blank, and max speed is restricted to 125mph. If CCTC cab signal is also inoperative then speed is restricted to 79mph, and additional dispatcher clearance is required if cab signal equipment has failed just on the train.

1. ACSES - Advanced Civil Speed Enforcement System

2. PSR - Permanent Speed Restriction

3. TSR - Temporary Speed Restriction

4. MAS - Maximum Allowed Speed

5. ADU - Advanced Display Unit

6. ATC - Automatic Train Control

7. CCTC - Continuous Coded Track Circuit

BTW, on the real railroad ACSES is not yet turned on between Fair and Philly AFAIK. It will be turned on within the next year. They have been installing the transponders for the last month or so.

The next question is about signal speed. In normal railroad signals, I understand that if you get some sort of restricting aspect, you're supposed to pass the next signal at say 30mph and you have the entire block to slow down, so in theory, you could run maximum allowed speed right to the last second, then cut in full service braking and pass the signal at exactly 30mph. In-game however, any signaling speed changes require you to apply full service braking within a few seconds or it will apply the brakes (though not emergency brakes) if you've activated speed control. On the real NEC, are signal-speed changes regarded as immediate reductions, or is the speed reduction only required to be in force once the train has passed the signal?
That is because the cab signal does not show the state of the signal that you are facing ahead of you (i.e. the next signal), but it shows what the state of the signal that you passed last would be if you were not occupying the block (i.e. what is the state of the signal that is ruling the current block). So any change in cab signal has to be acted on immediately. A cab signal is not a track side signal. This is so because the NEC cab signal system does not provide distance to next signal, so from the perspective of automatic train control it is useless to know what the state of the next signal is, since the computer does not know how far away it is. The exception to this is if the next signal is red in which case the cab signal transitions to restricting (no code) at some point ahead of the next signal.

Another difference BTW between just classic CCTC Cab Signal and that with ACSES overlay is, absent ACSES, Cab Signal will allow you to pass a stop signal at restricted speed, but ACSES will enforce a stop at a home signal that is indicating stop. Again, this is on the real railroad. I have no idea what the game does.
SO when Im playing MSTS the cab signal in the acela is fake? It shows what the upcoming signal is.
 

jis

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SO when Im playing MSTS the cab signal in the acela is fake? It shows what the upcoming signal is.
If that is what it shows, then it is fake. The PRR cab signal shows the current ruling signal, not what the ruling signal will be in the next block.

Even otherwise one is supposed to operate according what the current ruling signal is. If you are facing a stop signal ahead, your current ruling signal is (usually) an approach, which means you are supposed to proceed ready to stop at the next signal. You are not supposed to stop dead as soon as you see a stop signal ahead.

The PRR cab signal actually provides for a short overlap segment where if the signal ahead is stop then cab will drop to restricting (i.e. no code) to enable enforcement before the signal is passed. For other signals, the ruling signal in a section informs about what needs to happen by the time you get to the next signal. However PRR cab signal aggressively enforces what is supposed to happen by the time you get to the next signal in terms of speed at which it should be passed etc. It does so because it does not have information about the distance to next signal. Hence it is more conservative than what NORAC allows absent cab signal.
 
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jis

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By the way... Moderators.... Could you change the word ASCES in the title to ACSES, which is what the OP intended to say. There is nothing that is called ASCES that is of any relevance to the question at hand. ACSES stands for Advanced Civil Speed Enforcement System, which is an overlay on top of the PRR cab signal system and it enforces speed limits and absolute stop at home signals.
 
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PerRock

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the Trainz P32-ACDMs have cab signaling in them for the NEC. However I don't usually run them (especially with the system set up) so I cannot confirm how they work. The best I can do for the moment is show a picture and say that N3V (formerly Auran) claims that it works correctly.

http://img375.imageshack.us/img375/3772/trainz201009111053333.jpg

I know our old Acela model doesn't have working cab signals. I'll have to check on our 3 different AEM-7 models & our HHP-8 model.

peter
 

MattW

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Thanks for the great post Jis! I used the knowledge in your post and ran another NEC scenario with your information. It does look like the modeled signal system is remarkably close to what you describe with a few exceptions likely to make development easier (lack of "dedicated" Approach Medium before Elizabeth for example). It also means most of the complaints by other users have been quashed as useless hogwash from lazy people wanting to be spoonfed :p

(also, thanks for pointing out the ASCES to ACSES in the title)

Thanks very much!
 

George Harris

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An engineer is supposed to know his territory before he is turned loose. There have been speed boards for curves and otherwise in place for at least 40 years. That I have seen.

Besides, as Jis says,you are not going to hit a stop signal at the end of a clear block, you will have an approach that tells you to be prepard to stop at the next signal.
 

amtrakwolverine

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They way the cab signals worked in MSTS was it would show the signal coming up as green and once I passed that signal if the next one was approach it would show that.
 

jis

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In that case the MSTS cab signal does not match reality as obtained on the NEC. Typically more sophisticated cab signal systems like TVM430 used by the French on the TGVs and Eurostar display a cotinuous target speed and a speed curve that must be followed, and if the engineer deviates from the target speed curve beyond a threshold the train takes over and enforces a safe speed curve to a dead stop (penalty stop). Such stops are not a good career move for an engineer.

Thanks for the great post Jis! I used the knowledge in your post and ran another NEC scenario with your information. It does look like the modeled signal system is remarkably close to what you describe with a few exceptions likely to make development easier (lack of "dedicated" Approach Medium before Elizabeth for example). It also means most of the complaints by other users have been quashed as useless hogwash from lazy people wanting to be spoonfed :p

(also, thanks for pointing out the ASCES to ACSES in the title)

Thanks very much!
Thanks for your kind words, and you are most welcome.

The dedicated Approach Medium at Elizabeth is actually an anomaly. It is said that it was introduced after an Amtrak jock allegedly tried to take the Elizabeth curve at 100mph and almost derailed the train. It is said that it was a testimony to the stability of AEM-7s and Amfleet on the track and the solidity of concrete tie anchored track that saved the day and the train made through without falling off the track. The track in question had to be realigned after the event according to the story.
 
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jis

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To answer to the original question regarding track speed (known technically as Civil Speed), in ACSES, the Civil speed is defined as the lowest of the Cab Signal Speed, PSR(2)s picked up from transponders and TSR(3) fed to the train by radio link or transponders, and the MAS(4) for the train class. The last bit is usually specified also as part of the PSR and TSR message anyway. The message contains speed info for 5 different train classes. This computed (Civil) speed is the speed at which the train is allowed to operate on the segment of track irrespective of the possibly more liberal Cab Signal speed, and is displayed in the Civil Speed display on the ADU(5). Note that PSR delivered from Transponder does not necessarily apply to the entire section. The transponder message contains information about what sub section the PSR applies to and the train ATC computer displays the right speed for each point of the track as the train proceeds down the track.
Reading the article on ACSES in the latest Trains magazine I realized that in my previous post there is an error in the paragraph excerpted above.

Civil Speed is actually defined as the maximum allowed speed at that location with a clear signal, for that class of train. What I erroneously said is the Civil Speed actually is the current allowed speed, i.e. the computed speed which is minimum of all the speeds mentioned. Civil Speed is the minimum of only the last three items mentioned. It does not include the signals speed.

The rest of the para is more or less correct.

Sorry about the error. I have corrected the original post to be in line with the description in the Trains article.
 
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G

G. Gibbs

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This thread, about Frankford Junction, seems very poignant now.
 

CHamilton

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A short, non-technical introduction to ACSES may be found here. It seems like a good overview to me, but those who have more knowledge than I do can chime in.
 

jis

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That article gets confused between whether PTC is installed on train or track. Actually the train is fully equipped for ACSES. Indeed, no Amtrak train on the NEC is allowed to depart its origination station unless ACSES is fully operational on the train. It is that track segment that does not have ACSES service available at present, but will have it by the end of the year.

And by the way, the federal mandate is only for main line tracks where trains operate at speeds greater than 125mph at the present time. The more general mandate begins on 1st January 2016. So at the present time there is no mandate or requirement for ACSES to be operational on the track segment involved in the accident.
 
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