I do most of my train watching along single track railroads in central and south Texas.
When a train passes a green signal, it turns red. Assuming there are no other trains on the route at the time, in either direction, how long does the signal stay red before it turns off?
Also, how far in advance of an oncoming train does the signal switch on?
Some territories have āconstant litā signals, other territories have āapproach litā signals. Approach lit signals will turn on when a train enters the track segment in advance of the signal. The signal will display the condition of the next 2 or 3 track segments beyond the signal.
When a train occupys the track segment beyond the signal - the signal will display its most restrictive indication. When a train is occupying the 2nd track segment beyond the signal it will display some form of a Approach indication (be prepared to stop at the next signal). When a train is occupying the 3rd track segment beyond the signal, depending on the signal system being used it will display Clear or Advance Approach (proceed at maximum authorized speed prepared to comply with Approach indication at next signal).
With Approach Lit signals, when the train that lit the signal passes out of that track segment - the signal will extinguish. With constant lit signals, the signal will display a Red indication as long as the track segment beyond the signal; it will display some form of a Yellow indication when the train clears the track segment beyond the signal, it will display a Green indication when the train clears the 2nd track segment beyond the signal.
The Signal System on the railroad you are viewing may be different. This discussion DOES NOT interject how signals operate at or in approach to Control Points, where the control operator controls the lining of routes and signals.
Track segments are the distance between āIntermediateā signals. The placement of Intermediate signals is a function of the speeds and train sizes that operate on a given territory and are predicated on service braking conditions of a maximum size train operating at maximium authorized speed
BaltACD,
Thanks for your thorough and helpful explanation.
PTC will light up our approach lit signals for six miles ahead of the train.
Jeff
And my grandson and I really appreciate that factā¦ [:D]
I am still foggy on what the difference is between an intermediate signal and a home signal.
Balt, could you explain this?
It sort of seems to me that itās all kind of a moving target, in that every signal is an āintermediateā signal in relation to the next one beyond it, as a train moves along.
What sets a āhome signalā apart from the others?
Canāt answer the home signal question. I think I know, but not authoritatively.
Watching the Deshler railcams has been an education on signals. Deshler is an interlocking, thus subject to the whims of the dispatcher - but still subject to track occupancy.
All signals at Deshler normally reside at āstop.ā When the dispatcher lines a train through, the route will get the least restrictive aspect possible at that moment.
Iāve seen the southbound CPLs at Deshler cycle through a full range of possible aspects. Train 1 will get a clear headed south and proceed through. Train 2 may be hot on their heels, or the DS may just be pre-loading the next route. The DS will line Train 2 though even as Train 1 is passing through the interlocking.
The first aspect weāll see will be ārestricting.ā Train 1 is still in the protected block, but this will allow Train 2 to enter the block at restricted speed. Usually Train 2 isnāt there yet, so weāll see the signal change to āapproach,ā and then to āclear.ā
On a clear day - especially in the evening - you can usually see the next signal going south on the cam.
Once clear of the interlocking, Iām sure the signals are along the line described by Balt, with a two or three block sequence.
With some exceptions, (Iām sure)*
Home signals are at dispatcher-controlled interlockings. Intermediates are the ones in between (normally have number plates) - also referred to as āautomaticsā.
*2 most dangerous words on the railroad are āalwaysā and āneverā.
Helps to understand the principle behind ABS vs. fixed locations.
The pinciple of an automatic block system is to keep moving trains separated by at least the fixed distance assigned to the āblocksā (think of them like building-blocks of a route, not āblockā in the sense of stop) net of physical stopping time. In normal practice, if you see āredā it indicates there is a train somewhere in the physical block immediately ahead of you; yellow means in the block ahead of that one; green means at least two are unoccupied.
This does not mean that green means āclear routeā. Patenallās system for B&O improved on the ABS idea to permit route signaling: when you see a green anywhere on a CPL system it means explicitly that a train is cleared to proceed ā as one old &O engineer said āif I see a green anywhere I go like hell!ā All the other blocks ā¦ whether vacant or occupied ā¦ are signaled red. (Of course the automatic feature still shows red/yellow as appropriate on āpermittedā route if there is something occupying the track, or some kind of circuit fault).
The āhomeā and ādistantā signals control the blocks leading up to some fixed feature requiring controlled access ā a crossing at grade or drawbridge, for example. The āhomeā signal is the one governing actual access āacrossā the protected stretch; the ādistantā is the warning that would let you stop in time (i.e. within āone blockā) if the āhomeā is red.
The principle of what to do at a āredā signal may differ a bit, with some railroads allowing something like āstop and proceed at restricted speedā into a red automatically-signaled block while requiring a full stop at a fixed home signal (which is, like a traffic light, govern
With cab signals we have 562 signalling - we have stretches of railraod with just home signals and cab signals. No intermediates at all. Other places you have one intermediate preceding the interlocking.
With PTC, will we get to the point where the signals will all be just on the screen and not standing in real life?
There was some intensive discussion of this precise point over the years of various flavors of PTC before the current āmandate but with overlayā business.
As I understand it, there will always be fixed indications at those āhomeā locations where an absolute stop is necessary if the route is not lined to proceed. This is not just as a ābackupā to internal PTC operation; while it mirrors what the PTC cab/computer display indicates, it is still a fixed indication that crews will have to observe, call (or point and call for Big Brother, etc.)
This will probably not be true for things like crossovers used for CTC routing, although in my opinion it probably should be. Part of the reason for eliminating fixed intermediates is that as you go to a CBTC model the effective block length can change, so having any fixed-length signal confusion is counterproductive ā¦ but you still need hard indication for potential physical full stops.
In theory laws could be passed to get rid of waysides altogether, both as block signaling and as route indication, and rely upon reasonably-robust cab signaling or CBTC for all running indications. In a perfect world that would be just great. However, the first time thereās an accident on a crossing or bridge or whatever, look for the lawyers to be seeking blood of whoever was responsible for the ideaā¦ or treasure from any railroad trusting enough to implement it.
I run on cab signal territory without waysides. We know where the cut sections are (easy enough when you know what to look for).
I wouldnāt put it past them to get rid of waysides in the near future.
Even with cab signals with no waysides you still have defined signal blocks. I used to know where all the boundries were, but have forgotten many of them now. When I started, most of the exCNW across Iowa was ATC/cab signal with no waysides. The few control points and some short areas where non-equipped engines to/from auxilary lines used a portion of the main had waysides.
When UP started expanding the CTC on the exCNW they added waysides. In a way itās more flexible when the cab signal fails. Without waysides if the CS failed you could only move at restricted speed until you received an absolute block. If their was a train between you and the next point (generally some kind of controlled point) that they used for limits of absolute authority, they couldnāt issue an absolute block.
With waysides in the same situation they can issue authority with instructions to follow the rule that doesnāt allow passing restricting/restricted proceed/stop and proceed without further authority. With waysides and no absolte block you can also proceed on those waysides not to exceed 40 mph.
With an absolute block and no waysides, speed is limited to 49 mph. With an absolute block and waysides, speed is limited to 79 mph.
I work with GCOR. I believe the rules Zug works with may be somewhat different.
Jeff
Technically, under our rule book, we have neither āintermediatesā or āhome signals.ā
Intermediate is a term people in the field started calling regular ABS signals between controlled points. Signals at their most restrictive normally allowed being passed under the rules without dispatcher authority.
Home signal has passed out of general usage. I have a 1968 Uniform Code that I carry with me and it no longer has Home signal in the definitions. I know older editions of the UCOR, and other rule books, had it. I bet most current working employees (at least where I work) wouldnāt have a clue as to what a home signal was if you asked them. Iāll ask my conductor when I go to work in a couple of hours.
Absolute signal somewhat fills in for home signal. However, not all absolute signals are controlled. The non-controlled ones can be passed in some situations under the rules without further authority.
Jeff
Railroad rule books that I am familiar with identify two kinds of signals - Absolute and Intermediate. Intermediate signals have number plates attached to their signal mast that display numbers, normally the Mile Post of the signals location. Absolute signals do not have number plates. The most restricive indication from a Intermediate Signal is Restricted Proceed. The most restrictive indication from a Absolute Signal is STOP! To pass a Absolute Stop signal, the train must get specific instructions from the control operator.
Note - in todayās world 99% of the time the control operator is the Train Dispatcher, however, there are still a few locations where the Operator position controls switches and signals, at the direction of the Train Dispatcher.
For the most part, Absolute Signals are the signals at control points that, in addition to the switches, are manipulated by the control operator to hold or move trains on lined routes. In many cases, the Absolute signals for a control point are referred to as Home Signals.
In non-signalled territory there are railroad crossings at grade that are protected by interlocked signals. These absolute signals are normally āprotectedā by a Distant Signal - that normally displays a āRestrictingā indication to approach the next signal prepared to STOP.
From what I have observed in my travels, all railroads in the USA follow the convention of no signal numbers on absolute signals, and numbers on the intermediate signals, with an odd digit at the end of the number(nearest odd tenth of a mile) for signals going away from the zero milepost and an even digit at the end of the number (nearest even tenth of a mile) for signals going towards the zero milepost. To add clarity, when all tracks are signaled for traffic in both directions, each numbered signal has the number of the track it controls in its number.
And, also from observation, in Canada, you can expect all signals to be numbered and, as I recall, absolute signals have two or more heads whereas intermediate signals have one head each (one of our good friends up north described the distinction in response to a question I asked several years ago).
Thanks to everyone for the very thorough responses.
A couple of questions.
What does the term āabsoluteā block mean?
And, Jeff, you mentioned a situation in which a train can pass the most restrictive aspect without permission of the dispatcher. I donāt get that. You mean, even if itās red? It seems Iāve read about passing red signals, but my impression was that first the train had to come to a complete stop, and then had to proceed at the speed (I canāt remember the term) which assures that the train can stop within half the distance of the engineerās vision. Is that what you were referring to?
The most restrictive signal a signal with a number plate can display is Restricted Proceed - signal can be passed without stopping and not exceeding Restricted Speed (15 or 20 MPH depending on whose rules are in effect) and being able to stop within 1/2 the range of vision. The Dispatcher does not need to be contacted to pass a āredā signal with a number plate. The Dispatcher must be contacted and must issue authority for a train to pass a āredā signal WITHOUT a number plate.
Absolute Block basically goes back to the days of the Manual Block system. Blocks could be āgivenā to a train as Clear or Occupied (note these blocks apply to trains moving in the same direction). A train operating with a Clear Block is being told that there are no trains ahead. A train operating with a Occupied Block is being told that their are train(s) ahead. In the days of Manual Blocks, trains had to provide Flag Protection against following trains - unless - the train was given a Absolute Block - which meant that no trains would be permitted to follow the train holding the Absolute Block.
Wh
LO: Hereās the current NORAC Signal Chart (which youāve probably already seen a version of for one railroad or another). The various aspects are explained. While there are variations by railroad, the basics are there.
One condition that isnāt shown there but I know is in use at least on CSX is the āGā marker on the signal mast signifying a grade. As I recall, a tonnage train (and possibly others) can pass such a signal without stopping, albeit at restricted speed.
Larry, did you forget a link?