Several people have asked recently why PTC does not absolutely preclude collisions between trains at restricting speed.
I'm not a PTC expert so someone who knows more can correct me. But the simplest explanation is that the PTC data network is basically one way: data goes to the train from either the railroad's communication network or the signal infrastructure, but it does not go the other way. The infrastructure passes its information to the train, the train determines its own position using GPS, and from those two sources of info the on-board computer enforces the various signal indications, authorities, and restrictions.
I'm not saying there aren't radio communications going in both directions - presumably the train can acknowledge having received a message and things like that. But I'm fairly certain that the system does not require a train to send vital, real-time location information back over the PTC data network. So in fact PTC doesn't give Train A any information about Train B's location. Train B's location is known in the same manner as before PTC came along: track circuits in signaled territory, track warrant limits in dark territory. So the way you pull up close to another train is the same as it was before: go slow enough to stop before hitting whatever might be out there, wherever it might be within the block.
Yes, there probably are ways to enhance the current system to prevent some additional low-speed collisions. My bet is that you would have to more or less implement moving blocks, which is to say, it's a long way off.
And finally it's worth pointing out that Restricted Speed is required to prevent or mitigate many things besides train-to-train collisions: broken rail derailments, train vs runaway rail cars or cars improperly left on the track, trains vs MOW equipment, trains versus track or signal workers. Incorporating these into even a really fancy PTC system would be very tricky indeed.
Dan
Increasing levels of complexity result in increased level of cost.
How much PTC safety can you afford to buy? How much would the additional complexity add to the time necessary to implement the finished product?
Remember, PTC as a product - DID NOT EXIST - when Congress mandated it without providing the railroads any funding mechanisms to get the job done. A number of disjointed technologies that can be brought together after much hard work did not make interoperable PTC a easy product to design, standardize and implement on the Class 1 railroads. Note - what Amtrak has implemented on the NEC as their version of PTC is not interoperatable with the form of PTC that the Class 1 railroads are implementing on their properties and the systems that the Amtrak Long Distance (non-NEC) trains must operate on.
PTC is a involved system at present. I suspect, over time, enhancements will be made as the carriers see opportunities to make PTC more effective and ALSO reduce the costs of operating trains and maintaining signal systems.
Never too old to have a happy childhood!
That's kind of a funny question to ask. Operating under a resticting indication implies the condition of the track ahead is unknown. For a PTC movement authority to be given, you have to know the route is clear to the end point of the authority.
PTC can't enforce restricting because there's no way of knowing the end point of the authority.
A train running in PTC mode might have to make a move governed by a restricting indication, such as entering a yard, but at that point it is no longer on PTC covered track.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
There is two way communication from the train to the back office. Trains have to tell the back office that the data has been received and is in good shape. Train also have to "release" the movement authorities they have used. Kind of like reporting clear in manual block.
oltmanndThere is two way communication from the train to the back office. Trains have to tell the back office that the data has been received and is in good shape. Train also have to "release" the movement authorities they have used. Kind of like reporting clear in manual block.
Trains don't do the reporting - track circuits in signalled territory do the reporting. Train crews do the reporting in TWC territory.
oltmanndPTC can't enforce restricting because there's no way of knowing the end point of the authority.
I would submit that PTC can't enforce restricted speed because it doesn't have eyes.
The limits of restricted speed may be known. What is not always known is the conditions that require it. This would be why PTC would only enforce the maximum allowable speed under restricted speed.
This could occur on main track.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
tree68 oltmannd PTC can't enforce restricting because there's no way of knowing the end point of the authority. I would submit that PTC can't enforce restricted speed because it doesn't have eyes. The limits of restricted speed may be known. What is not always known is the conditions that require it. This would be why PTC would only enforce the maximum allowable speed under restricted speed. This could occur on main track.
oltmannd PTC can't enforce restricting because there's no way of knowing the end point of the authority.
Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits? For the latter, PTC needs to be given eyes in the form of optical sensors. As I mentioned in the other thread, there is no limit to amount of sensor coverage and sensor capabilities that could be applied to a railroad corridor. Sensors could be added to trains and also placed wayside to provide a fixed grid. They could sense anything that humans can see plus many things that humans could not sense.
Taken to its logical conclusion, it will be PTC that will ultimately decide what condtions require restricted speed; and it will be PTC that will then enforce restricted speed. So there will be no need for end points of authority because the application of restricted speed will be fully automated.
BaltACD oltmannd There is two way communication from the train to the back office. Trains have to tell the back office that the data has been received and is in good shape. Train also have to "release" the movement authorities they have used. Kind of like reporting clear in manual block. Trains don't do the reporting - track circuits in signalled territory do the reporting. Train crews do the reporting in TWC territory.
oltmannd There is two way communication from the train to the back office. Trains have to tell the back office that the data has been received and is in good shape. Train also have to "release" the movement authorities they have used. Kind of like reporting clear in manual block.
Correct, but PTC does it, too. It's not "vital", but PTC won't let out another movement authority for a following train until the leading train "clears up" behind it. It's "both/and" the way I understand it.
I wonder if PTC does enforce slow speed when restricting speed is indicated (such as being "talked by" a stop signal? Anybody know?
EuclidAre we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits? For the latter, PTC needs to be given eyes in the form of optical sensors.
I think we are talking about the mandated PTC. Restricted speed was exempted from PTC except control of max. speed during the law making process for cost and time reasons.
PTC systems can be designed to know the rear end of a train. Look at stand-alone systems allowing moving block like the approved CBTC. https://en.wikipedia.org/wiki/Communications-based_train_control
I-EMTS is not able to this in its current design status.
There will still be reasons for restricted speed like broken rails that might not get detected precisely enough to use PTC.
A differently mandated PTC could have prevented the Arizona accident, I think.
The upper limit of restricted speed is controlled by PTC according to 49 CFR §136.1005 (f): https://www.law.cornell.edu/cfr/text/49/236.1005Quote: (f)Train-to-train collision. A PTC system shall be considered to be configured to prevent train-to-train collisions within the meaning of paragraph (a) of this section if trains are required to be operated at restricted speed and if the onboard PTC equipment enforces the upper limits of the railroad's restricted speed rule (15 or 20 miles per hour)............Regards, Volker
oltmannd tree68 oltmannd PTC can't enforce restricting because there's no way of knowing the end point of the authority. I would submit that PTC can't enforce restricted speed because it doesn't have eyes. The limits of restricted speed may be known. What is not always known is the conditions that require it. This would be why PTC would only enforce the maximum allowable speed under restricted speed. This could occur on main track. I wonder if PTC does enforce slow speed when restricting speed is indicated (such as being "talked by" a stop signal? Anybody know?
Slow Speed and Restricted Speed are not the same. When operating at Slow Speed there is no requirement to be on the lookout for the things that are mentioned in the rule book definition of Restricted Speed.
People first have to define what they mean by "enforce restricted speed".
Restricted speed is designed to intentionally allow "collisions" between equipment.
A train is made up of individual cars and engines. In order for them to operate as a train they have to intentionally "collide" to couple. If you prevent all "collisions", you will prevent equipment from coupling up.
The difference between a "coupling" and a "collision" is intent. PTC can't detect intent.
Dave H. Painted side goes up. My website : wnbranch.com
VOLKER LANDWEHR Euclid Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits? For the latter, PTC needs to be given eyes in the form of optical sensors. I think we are talking about the mandated PTC. Restricted speed was exempted from PTC except control of max. speed during the law making process for cost and time reasons.
Euclid Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits? For the latter, PTC needs to be given eyes in the form of optical sensors.
I think that is the correct interpretion of most references here to PTC. But I also think it is important to make the disctinction since there is a lot of oppostion to PTC because it has been mandated. And this opposition naturally results in trying to downplay the benefits of the PTC concept. So when people say "PTC can't do" this or that, it may be encouraged by active opposition to PTC because of resenting the mandate. So, in such a case, it serves the argument to leave out the qualification that the cited limitation only applies to the mandated PTC.
EuclidEuclid Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits?
You asked, I answered.Regards, Volker
VOLKER LANDWEHR Euclid Euclid Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits? You asked, I answered.Regards, Volker
Euclid Euclid Are we talking about PTC as defined by the mandate or PTC as defined by its conceptual limits?
Oh that's fine. I appreciate your ansnwer. I was just using it to frame the reason I asked the question.
dehusmanPeople first have to define what they mean by "enforce restricted speed". Restricted speed is designed to intentionally allow "collisions" between equipment.
We are not talking about intended collisions/couplings but "restricted speed", a speed that will permit stopping within one-half the range of vision.
What PTC is required to do at "restricted speed" is found in 49 CFR §236.1005 linked above.
Coupling cannot prevented by PTC as long as it doesn't know the location of every single car. That is unlikely to ever come.
At best it will perhaps sometime know the location of head end and rear end of a train to prevent "restricted speed" accidents like in Arizona.Regards, Volker
VOLKER LANDWEHRWhat PTC is required to do at "restricted speed" is found in 49 CFR §236.1005 linked above.
Then you are only discussing trying to prevent collisions between trains operating in signaled territory or on a joint authority mandatory directive.
This discussion then would not consider collisions in non-signalled territory, in tracks other than a main track or in yard limits, all of which would fall outside the scope of 49 CFR 236.1005.
That still presents the problem that you have to allow two pieces of equipment to (trains, engines or cars) to be able to come in contact with each other when operating in a signal system or in a joint manadatory directive. How do you tell the PTC system that you are adding an engine to the train intentionally, and that it is not a case of an engine running into a standing train? The difference between a collison and a coupling is intent.
BaltACD oltmannd tree68 oltmannd PTC can't enforce restricting because there's no way of knowing the end point of the authority. I would submit that PTC can't enforce restricted speed because it doesn't have eyes. The limits of restricted speed may be known. What is not always known is the conditions that require it. This would be why PTC would only enforce the maximum allowable speed under restricted speed. This could occur on main track. I wonder if PTC does enforce slow speed when restricting speed is indicated (such as being "talked by" a stop signal? Anybody know? Slow Speed and Restricted Speed are not the same. When operating at Slow Speed there is no requirement to be on the lookout for the things that are mentioned in the rule book definition of Restricted Speed.
Understand completely. You can never exceed "slow" speed when operating under restricting. Slow implies a clear route. Restricting does not. PTC can't do restricting.
oltmanndUnderstand completely. You can never exceed "slow" speed when operating under restricting. Slow implies a clear route. Restricting does not. PTC can't do restricting.
Slow speed under NORAC is not to exceed 15mph. Restricting can allow up to 20mph unless there's other considerations ( for example - through interlockings for us).
But then again - restricted speed is not a speed; but a method of operation. Slow speed is just that. A speed.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
zugmann oltmannd Understand completely. You can never exceed "slow" speed when operating under restricting. Slow implies a clear route. Restricting does not. PTC can't do restricting. Slow speed under NORAC is not to exceed 15mph. Restricting can allow up to 20mph unless there's other considerations ( for example - through interlockings for us). But then again - restricted speed is not a speed; but a method of operation. Slow speed is just that. A speed.
oltmannd Understand completely. You can never exceed "slow" speed when operating under restricting. Slow implies a clear route. Restricting does not. PTC can't do restricting.
CSX Rules define the upper limit of both Slow Speed and Restricted Speed at 15 MPH. Needless to say Restricted Speed has all the other conditions attached to it and Slow Speed does not have those conditions.
zugmannBut then again - restricted speed is not a speed; but a method of operation. Slow speed is just that. A speed.
For us, restricted speed is not to exceed 10 in the yard (by timetable instruction), and 20 on the main. NORAC calls for 15 in interlockings.
I haven't done a detailed search, but I don't think the word "restricting" appears in NORAC. I could be wrong.
dehusmanThen you are only discussing trying to prevent collisions between trains operating in signaled territory or on a joint authority mandatory directive.
This thread started as follow up to the Arizona accident thread where the question arose if PTC had to prevent that accident. This thread was the attempt to bundle the answer.
That doesn't mean the discussion is limited to this topic. In this light I didn't understand your post. As Zugmann said "restricted speed" is an operation procedure not a speed.
dehusmanThis discussion then would not consider collisions in non-signalled territory, in tracks other than a main track or in yard limits, all of which would fall outside the scope of 49 CFR 236.1005.
If I understood PTC correctly dark territory is not exempted from PTC when it fulfills the requirements that make PTC necessary in signaled territory. The dispatcher still issues track warrants by voice/data radio und PTC enforces the movement authorities. Mainline switches and derails must be tied into the PTC system.
A stand-alone system would be able to avoid train collisions in dark territory too. A reworked I-EMTS might be able sometime too.
In my point of view the PTC mandate was kept as small as possible, enough to prevent those accidents that endanger train passengers and the public most. Accidents among railroaders were not considered important enough, I fear.
dehusmanHow do you tell the PTC system that you are adding an engine to the train intentionally, and that it is not a case of an engine running into a standing train? The difference between a collison and a coupling is intent.
With the permission of the dispatcher the PTC system can be cut out. Here are some PTC locomotive displays: www.smartlocal202.org/site/assets/files/BNSF/BN_ROAD/PTC_Screen_Elements_9_27_2012.pdf
On page 1 under PTC-System States it shows "Cut Out" with the above explanation.Regards, Volker
zugmannSlow speed under NORAC is not to exceed 15mph. Restricting can allow up to 20mph unless there's other considerations ( for example - through interlockings for us).
Interesting. Restricting on Conrail had a max of 15 mph. Slow speed was 15 mph...
oltmannd BaltACD oltmannd There is two way communication from the train to the back office. Trains have to tell the back office that the data has been received and is in good shape. Train also have to "release" the movement authorities they have used. Kind of like reporting clear in manual block. Trains don't do the reporting - track circuits in signalled territory do the reporting. Train crews do the reporting in TWC territory. Correct, but PTC does it, too. It's not "vital", but PTC won't let out another movement authority for a following train until the leading train "clears up" behind it. It's "both/and" the way I understand it.
Again, I'm no expert, but I'm pretty sure that's not true. It is possible that PTC will raise a warning if a train crew tries to release an authority while they're still within its limits.
But preventing a premature release of authority is actually quite different from what you said - namely, that PTC would prevent the dispatcher from issuing an authority to another train. That is not the role of PTC, but of the Computer-Aided Dispatcher (CAD) software on the dispatcher's workstation. These systems were pretty sophisticated well before PTC came along. PTC doesn't control the issuance of authorities, just keeps trains within their authorities.
As I said at the top, it seems to me that preventing train-to-train collisions at restricting speed would require you to implement most of what you would need for moving block. The only thing PTC can do is ensure that each train stays within it's limits, so the only way to keep two trains from ever being in the same place at the same time is to never have overlapping limits. The only way to let trains get very, very close to each other without overlapping limits is to have authority limits that tightly match your trains exact location - which is basically what a moving block is..
Some others have suggested that it was a "choice" to implement PTC in the way it was implemented, and in some sense that's true. But the choice was dictated by the desire to have PTC invented and installed from 0 to 100% in seven years (later extended to ten years). At the time, there were, what, three systems in revenue service on the North American railroad network (not counting PATH) that had most of the desired safety features for PTC (ETMS, ASCES, ITC). All of them used basically the same block-system paradigm, and none of them had any ability to do moving blocks (or to prevent all train-to-train collisions at restricting speed). The notion that a moving block system, which had been tried and failed several years earlier in the NAJPTC project, would be invented from nothing and deployed nationwide in seven years was apparently so ludicrous that even Congress accepted it.
BN had experimented with ARES, a stand-alone system. The merger with ATSF ended the project.
There would have been a starting point for a stand-alone system. It is said it would have been too expensive and time consuming to finally develop it.
Wagging tongues suggest that tasking the signal departments with PTC development and implementation was the end of the stand-alone system as it would make many signals surplus.
Here is video about BNSF's PTC system: https://youtu.be/7fDRazEWAKURegards, Volker
PTC allows you pass an intermediate (non-absolute) signal at restricted speed. PTC gives a warning at 18 mph and initiates a brake application when speed goes over 21 mph, speeds as indicated on the PTC screen. (Speed on the locomotive's speedometer may differ by a few mph either way. My experience has been that usually the PTC indicated speed is 1 to 2 mph less than the locomotive indicated speed.) The same conditions apply when talked by an absolute signal.
Jeff
VOLKER LANDWEHR dehusman Then you are only discussing trying to prevent collisions between trains operating in signaled territory or on a joint authority mandatory directive. This thread started as follow up to the Arizona accident thread where the question arose if PTC had to prevent that accident. This thread was the attempt to bundle the answer. That doesn't mean the discussion is limited to this topic. In this light I didn't understand your post. As Zugmann said "restricted speed" is an operation procedure not a speed. dehusman This discussion then would not consider collisions in non-signalled territory, in tracks other than a main track or in yard limits, all of which would fall outside the scope of 49 CFR 236.1005. If I understood PTC correctly dark territory is not exempted from PTC when it fulfills the requirements that make PTC necessary in signaled territory. The dispatcher still issues track warrants by voice/data radio und PTC enforces the movement authorities. Mainline switches and derails must be tied into the PTC system. A stand-alone system would be able to avoid train collisions in dark territory too. A reworked I-EMTS might be able sometime too. In my point of view the PTC mandate was kept as small as possible, enough to prevent those accidents that endanger train passengers and the public most. Accidents among railroaders were not considered important enough, I fear. dehusman How do you tell the PTC system that you are adding an engine to the train intentionally, and that it is not a case of an engine running into a standing train? The difference between a collison and a coupling is intent. With the permission of the dispatcher the PTC system can be cut out. Here are some PTC locomotive displays: www.smartlocal202.org/site/assets/files/BNSF/BN_ROAD/PTC_Screen_Elements_9_27_2012.pdf On page 1 under PTC-System States it shows "Cut Out" with the above explanation.Regards, Volker
dehusman Then you are only discussing trying to prevent collisions between trains operating in signaled territory or on a joint authority mandatory directive.
dehusman This discussion then would not consider collisions in non-signalled territory, in tracks other than a main track or in yard limits, all of which would fall outside the scope of 49 CFR 236.1005.
dehusman How do you tell the PTC system that you are adding an engine to the train intentionally, and that it is not a case of an engine running into a standing train? The difference between a collison and a coupling is intent.
There are two kinds of cut out. "Soft" cut out and "Hard" cut out. There are conditions that require a soft cut out and can be done without permission. A soft cut out is performed by pushing the cut out soft key button. PTC asks if you want to suspend enforcement. Once the conditions for having to soft cut out end, another button (cut in) will re-establish enforcement, after asking if this is what you want to do.
Hard cut out is done by opening three toggle switches located in a sealed box in the nose. Each toggle switch is also sealed. The dispatcher's permission is required for this.
I've only had to hard cut out one engine. That was when, even in soft cut out, the PTC system was still cutting out the automatic air brake valve on the lead locomotive without warning or penalty.
jeffhergertThere are two kinds of cut out. "Sot" cut out and "Hard" cut out. There are conditions that require a soft cut out and can be done without permission. A soft cut out is performed by pushing the cut out soft key button. PTC asks if you want to suspend enforcement. Once the conditions for having to soft cut out end, another button (cut in) will re-establish enforcement, after asking if this is what you want to do. Hard cut out is done by opening three toggle switches located in a sealed box in the nose. Each toggle switch is also sealed. The dispatcher's permission is required for this. I've only had to hard cut out one engine. That was when, even in soft cut out, the PTC system was still cutting out the automatic air brake valve on the lead locomotive without warning or penalty. Jeff
And when I was still working - Dispatchers had to get permission from the headquarters locomotive mechanical staff - who would have been working with the engineer of the locomotive that was having problems before they could issue permission for PTC to be cut out.
I have ridden a train that stopped at a signal, anf then moved up slowly until it was close to another train on the same track. Three years ago, I was waiting in Providence for an NE Corridor train which was running late--and an MBTA train left Providence ahead of my train. Along the way, the MBTA train made a stop at one of its stations; we stopped at the block signal, and then crept up the MBTA train--and followed it into Back Bay and then on into South Station.
While walkng to the station, I came up with the engineer and asked if that was what he had done, and said that it was.
Johnny
jeffhergert oltmannd tree68 oltmannd PTC can't enforce restricting because there's no way of knowing the end point of the authority. I would submit that PTC can't enforce restricted speed because it doesn't have eyes. The limits of restricted speed may be known. What is not always known is the conditions that require it. This would be why PTC would only enforce the maximum allowable speed under restricted speed. This could occur on main track. I wonder if PTC does enforce slow speed when restricting speed is indicated (such as being "talked by" a stop signal? Anybody know? PTC allows you pass an intermediate (non-absolute) signal at restricted speed. PTC gives a warning at 18 mph and initiates a brake application when speed goes over 21 mph, speeds as indicated on the PTC screen. (Speed on the locomotive's speedometer may differ by a few mph either way. My experience has been that usually the PTC indicated speed is 1 to 2 mph less than the locomotive indicated speed.) The same conditions apply when talked by an absolute signal. Jeff
This is interesting. Thanks for taking the time to explain so clearly.
So, if there is a train in that block, does PTC try to enforce a movement authority to the end of that train or will it just let you run smack into it at 20 mph? That would kinda take the "positive" out of PTC.
I get the "talking by" an absolute. Signal could be broken - in which case PTC is, too. Or you could be tucking in a siding behind another train - which makes it look more like the first case.
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