I’m wondering if anyone can give me a quick, couple-sentence primer on the difference between automatic block signaling and centralized traffic control. I know both are designed to improve efficiency and safety, but I was trying to explain it all to my 6-year-old son who loves trains and I found that I really couldn’t accurately describe the difference. My apologies if this has been covered before in these forums, but any info would be helpful.
Thanks,
Ross R.
ABS is a protective overlay. ABS does not give trains authority. In ABS territory movement authority is given with Track Warrants or Direct Traffic Controll and the signals are a safety overlay to prevent trains from collisions. CTC signals give the trains authority to move by signal indication. In reality CTC is basicly ABS with controll points and remote switches (ABS almost always has manual switches).
Another way to look at it is that ABS is primarily a safety function – as Chad said, the idea is to prevent collisions by a system which senses, automatically, whether a block is clear or not, and sets signals accordingly.
CTC is a control function – it tells the crew when they may go, and determines which trains are allowed to move, and also sets where they go. It uses signals, too, but rather than responding to tracek and block conditions directly, the CTC signals respond to the dispatcher’s commands. The dispatcher also controls switches to route trains. The CTC signals are usually connected to an ABS system of some type, so that the dispatcher can’t tell a train it’s OK to head into an occupied block (generally regarded as bad form…) but they don’t have to be.
In reguards to CTC, CTC is Central Traffic Controll. That means one or more controllers is in a central location controlling a streach of track or tracks. There are different arangements for acomplishing this. Early CTC installations typicaly were custom designed and built controll panels with track diagrams containing a multitude of toggle switches to controll switch positions and signal indications and such and Lights indicating switch positions and track occupancy. These were usualy very big consoles that contained bulkey wireing and electronics and would often wrap around the operator over many feet of space. These were almost always located next to the track they controlled. Now with the PC these systems were not so much custom built machines as they were custom programmed computer systems that were tied into the physical plant by varying methods. This allowed the computer (and operator) to be located in locations distant from the physical plant. They became more and more flexable and intellegent as time and technology moved on. These days modern dispaching systems could in theory be ran by the computers themselves they are so sophisticated, But in reality I hear even the best automated dispaching systems need close human supervision. In the last couple of decades the bigger railroads have consolidated there dispaching centers into central locations like Omaha (UP) and Jacksonville (CSX) for efficiency. Although that trend has reversed and some railroads are decentralizing certain areas, Usualy in regional centers that are jointly operated by all the railroads of a given area, Like LA or Houston.
One of my favorite signaling web sites:
http://www.railway-technical.com/sigind.html
Some other pretty good web sites:
http://www.technology.niagarac.on.ca/people/mcsele/railroad.htm
http://broadway.pennsyrr.com/Rail/Signal/aspect_speeds.html
Also read review these topics that have been posted here in this forum:
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=51418
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=51645
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=52203
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=42350
I copied/pasted this text from one topic I replied in:
First there is a ton of info on this web site:
http://www.railway-technical.com/sigind.html
This is a very good first read for a ‘newbie’ regarding signaling, and Automatic Block Signaling (ABS):
http://www.railway-technical.com/sigtxt1.html
So here is my understanding of it:
Track is divided up into blocks which are monitored by block circuits. These blocks are ‘guarded’ by automatic signals. The ABS logic ensures (a) there is a safe spacing between two trains via an empty block, by issuing two red signals in a row, and (b) ensure that train #2 slows down in advance by issuing one or two yellow signals in a row. This is the basic fundamentals of ABS.
ABS functions on its own. It does not need to receive additional instruction from people. However, in the interests of being able to manually send information such as setting up routes, and giving a lagging priority train the opportunity to get ahead of a less priority train, the CTC is the system that lets RR staff do that. Scheduling of trains is just one thing of many things operators can use the CTC for.
The thing about ABS and CTC is that it keeps trains apart. There have been lots of research into finding ways to get more trains on the track, yet keep them safe via advanced signaling methods…so I suggest you read these only after you have read the ‘intro to signals’ stuff first. You will also know that many signal systems of today have many many aspects. This is to accomplish many things including increasing efficiencty, reduce hard braking, notify of possible taking a siding, etc.
Hope this helps!
So in other words CTC and ABS can work together. Do they work together all the time, or is that a personal prefferace (SP) of the railroad? That is interesting. I always thought that one type of signaling system overtook the other, meaning that a railroad would either chosse between having the Timtable and Train Orders, CTC, or ABS …ect.
Thanks much for all the info and links. It’s all very helpful!
Ross R.
Sarah, It’s one or the other. With ABS signal system there is no communication between the field and the dispacher. The signals do not give the train authority, that is given by the dispacher,the signals are added protection against collisions. In CTC territory the signals themselves govern movement authority. The reason I say CTC is ABS with controll points is basicaly because the ABS logic exists within the CTC system. But these days modern CTC systems are a lot more complex than that.
If you are sitting faceing a green signal in ABS territory that does not mean you have authority to move, it just means there are no trains in the next few blocks. If you are faceing a green in CTC territory that means
One analogy is that ABS is a completely automatic system, and in that sense only it is like your corner stop light that cycles to protect the crossing, but with the difference that the ABS system responses to the trains actually using the track to provide the protection. But a CTC system in some ways puts the dispatcher in the position of the owner of a large model railroad with many trains who controls the whole operation, but with the difference that only the switches are controlled directly in both the model railroad and the real thing, while singnals on the real railroad inform the engineers what to do with their trains. And, in fact, there were some low-cost CTC installations that did use, maybe still do, some hand throw switches, with signals informing crews how to throw the switches! Another analogy that might make sense is that the safety and control provided in the classic interlocking tower is extended to a whole division or divisions by the CTC system. With the dispatcher replacing the towerman.
[quote]
QUOTE: Originally posted by chad thomas
Sarah, It’s one or the other. With ABS signal system there is no communication between the field and the dispacher. The signals do not give the train authority, that is given by the dispacher,the signals are added protection against collisions. In CTC territory the signals themselves govern movement authority. The reason I say CTC is ABS with controll points is basicaly because the ABS logic exists within the CTC system. But these days modern CTC systems are a lot more complex than that.
If you are sitting faceing a green signal in ABS territory that does not mean you have authority to move, it just means
[quote]
QUOTE: Originally posted by ironken
[quote]
QUOTE: Originally posted by chad thomas
Sarah, It’s one or the other. With ABS signal system there is no communication between the field and the dispacher. The signals do not give the train authority, that is given by the dispacher,the signals are added protection against collisions. In CTC territory the signals themselves govern movement authority. The reason I say CTC is ABS with controll points is basicaly because the ABS logic exists within the CTC system. But these days modern CTC systems are a lot more complex than that.
If you are sitting faceing a green signal in ABS territor
Yep, that’s true Chad. 251 territory…now that is old school. After the GCOR bible was introduced, its now 9.14 territory requiring a 9.15 track permit to run against the current of traffic unless it is DTBABS, then no need for the track permit to run against the current of traffic. I think that the old Santa Fe rule book was a better gig. It fit in your pocket and was more straight forward and was also before my time. I have one laying around…wonder what it’s worth?
[quote]
QUOTE: Originally posted by chad thomas
[quote]
QUOTE: Originally posted by ironken
[quote]
QUOTE: Originally posted by chad thomas
Sarah, It’s one or the other. With ABS signal system there is no communication between the field and the dispacher. The signals do not give the train authority, that is given by the dispacher,the signals are added protection against collisions. In CTC territory the signals themselves govern movement authority. The reason I say CTC is ABS with controll points is basicaly because the ABS logic exists within the CTC system. But these days modern CTC systems are a lot more complex than that.
Tregertha,
Let me try a simple answer to your original question. The explanations of ABS others have offered are accurate. ABS is a train spacing system which also provides broken rail protection. In ABS the switches at the ends of siding are manually controlled. Authority to occupy the main track is not conveyed by signals. In the old days authoriuty was by timetable or train order. Today it is usually by track warrant.
In CTC the dispatcher controls both the switch position and the three absolute signals at each end of a siding, AND an absolute signal indication more favorable than stop conveys authority to occupy the track to the next controlled, or absolute" signal.
The defining difference is how authority to occupy the main track is conveyed. In terms of “look” it is how the switches are thrown and by whom. In the West block signals are designated by number plate and Absolute signals by lack of number plate.
Typically in a CTC system only the ends of sidings, and perhaps Junctions are control points. The signals between sidings are block signals just as in ABS.
Mac
Without getting off topic these can both be part of cab signaling or ATC/ ATS i.e. (train stop) systems. Yes it can get more confusing. I wonder why the child was confused??? ENJOY
Yes. Train stop systems are an optional addition to either/both block signals and CTC.
Mac
And, to either throw a monkey wrench into the discussion, or maybe clear things up a bit - a milepost marker on the signal mast has significance, does it not?
It prevents confusion and is almost always coordinated with the actual mileposts if any. It is good to give a signal maintainer data on a defective signal by the mileage marking since that tells him (or her) exactly where it is and gets him (or her) to repair it quicker.
I was thinking in terms of a red (stop) signal on a mast with a mileage sign is stop and proceed (NORAC Rule 291), whereas the same signal on a mast without the sign is absolute (NORAC Rule 292). Or something like that.