Why signals display stop commands, when there is no train for miles?

[tomikawaTT]

BT CPSO 266

I mean (for example) when I see a model train layout with a functioning signaling system, as long as the track is clear and the switches are not aligned to a different track, they seem to displaying clear signals. I know it is not real, but I just always wondered why the real railroads do not have this applied in their signaling systems. 

To boil down to the basics, ABS signals indicate the condition of the route ahead, but don't grant authority to use it.  Interlocking signals grant movement authority.

As for model railroad signallng systems, most are vastly simplified if not downright inaccurate.  OTOH, I have a fully prototypical 'end of the railroad' diorama which is fully interlocked.  All signals (lower quadrant 2-indication semaphores) display their most restrictive aspects until cleared, and clearing a signal locks all affected points and all opposing signals.  My prototype (a minor branch line terminal of the Japan National Railways) did this mechanically (hence my reference to, "Yard-long levers and brute force.")  I get the same results with contacts on switch and signal machines.

Chuck

[Falcon48]

BT CPSO 266

Ok, I understand now. The explanations and reasons are very logical, for operations.

I neglected to mention one other pretty important consideration.

On a rail line operated by CTC, the dispatcher uses signal indications at control points to confer movement authority.  The signals at these locations thus can't be left displaying permissive indications, because the indications would effectively be telling any approaching train that it had authority to proceed.  Rather, they display "stop" until the disptacher actually wants to authorize a particular train movement. 

This is in contrast to an ABS line, where the signals indicate occupancy and switch positions, but confer no movement authority.  Even if the signals are all green on an ABS line, the train still can't move until the train gets separate authority (typically in the form of a track warrant) from the train dispatcher.  On the ABS line, the signals can thus stay green if the tracks ahead are clear, sine the signals are not actually authorizing the train to proceed, 

[BT CPSO 266]

Ok, I understand now. The explanations and reasons are very logical, for operations.

[Falcon48]

BT CPSO 266

tomikawaTT

So, are there crossovers between multiple tracks, or to yard arrival/departure tracks, or a junction between routes? 

 

It multiple track @ ALTO, SLOPE is not an interlocking ONLY for WB trains going up track #3. 

I just never really understood, as long as the switch is not aligned against the track, why it does not display a clear signal, if there is not trains near the interlocking or any blocks further down the line that are tied into the it.

I mean (for example) when I see a model train layout with a functioning signaling system, as long as the track is clear and the switches are not aligned to a different track, they seem to displaying clear signals. I know it is not real, but I just always wondered why the real railroads do not have this applied in their signaling systems. 

It certainly would be possible for a "real" railroad to keep the signals at "clear" (or whatever the most permissive signal is) for one route through an interlocking at all times, except when a different routing is desired.  And there are probably places where this is done,  But here's the rub.  If you keep all the signals at "stop", then the dispatcher is free to quickly set up a route for whatever train he desires, regardless of other trains in the area.  However, if one route has always kept lined up, he has to take that route away before he can line up another route.  Depending on the design of the plant, and the location of other trains, this could require a timeout of several minutes before the new routing can be established. This feature is essential for "real" railroads, so that a dispatcher can't line up a conflicting train movement in the face of an oncomong train that's already been cleared through the plant.  I doubt that you see it much in model railroads

[BaltACD]

BT CPSO 266

Paul_D_North_Jr

The one at Summerhill may also be an 'intermediate' block signal, which are often "approach-lighted" - to save battery and bulb life, the signal lights up only when a train is approaching and is getting close from the direction that the signal faces.  When the train is past, or coming from the other direction, or is far away, the signal stays dark.

I had a filling it had something to do with saving bulb life, but still does not explain why the eastbound signals must always be on, when the westbound signals my be turned off.

Railroad signaling systems operate under one of two competing philosophies....Constant Lit Signals and Approach lit signals.  As I mentioned in my earlier post, different signal engineers have different philosophies, additionally as wear & tear overtakes the systems, parts that facilitate constant lit signals may have to be installed on approach lit signals, or vice versa,  in order to keep the system operating.  While it is unusual to have constant lit and approach lit signals in the same area, it is not unheard of.

[BT CPSO 266]

Paul_D_North_Jr

The one at Summerhill may also be an 'intermediate' block signal, which are often "approach-lighted" - to save battery and bulb life, the signal lights up only when a train is approaching and is getting close from the direction that the signal faces.  When the train is past, or coming from the other direction, or is far away, the signal stays dark.

I had a filling it had something to do with saving bulb life, but still does not explain why the eastbound signals must always be on, when the westbound signals my be turned off.

[Paul_D_North_Jr]

As Chuck said above, the signal at ALTO was acting like an interlocking signal would, but the one at SLOPE was acting like an 'intermediate' block signal would.

The one at Summerhill may also be an 'intermediate' block signal, which are often "approach-lighted" - to save battery and bulb life, the signal lights up only when a train is approaching and is getting close from the direction that the signal faces.  When the train is past, or coming from the other direction, or is far away, the signal stays dark.

See also the concurrent thread on "NS Signal Question" at -  http://cs.trains.com/trccs/forums/t/178562.aspx 

There are lots of other resources and explanations out the Internet.  Take a look at this one, too - Al Krug's explanation of "Railroad Signals" at - http://www.alkrug.vcn.com/rrfacts/signals/signals.htm   And this one - also on Railroad Signals - from Trains' "ABCs of Railroading" at - http://www.trains.com/trn/default.aspx?c=a&id=191 

- Paul North. 

[BT CPSO 266]

tomikawaTT

So, are there crossovers between multiple tracks, or to yard arrival/departure tracks, or a junction between routes? 

 

It multiple track @ ALTO, SLOPE is not an interlocking ONLY for WB trains going up track #3. 

I just never really understood, as long as the switch is not aligned against the track, why it does not display a clear signal, if there is not trains near the interlocking or any blocks further down the line that are tied into the it.

I mean (for example) when I see a model train layout with a functioning signaling system, as long as the track is clear and the switches are not aligned to a different track, they seem to displaying clear signals. I know it is not real, but I just always wondered why the real railroads do not have this applied in their signaling systems. 

[tomikawaTT]

There are probably two different signal logics involved:

1. Automatic Block Signal (ABS) usually display Clear unless there is some obstruction or another train ahead.  One at the approach to a slow-order curve might only clear to Pass at reduced speed prepared to stop at the next signal.  In short-block territory approaching a terminal there might be a whole pageful of increasingly restrictive indications.  (The JNR used five-lamp color light signals on the approach to Shinjuku Station.)
2. Interlocking signals control movement through an interlocking plant, which can range from a single turnout (to a branch line) to a multi-track puzzle palace of double slip switches at a major junction.  At an interlocking, ALL signals display Absolute Stop at all times EXCEPT when a route has been aligned and a train is cleared through it.  Then ONLY those signals controlling that movement may be cleared - and that action locks the switch points until the signals are returned to Absolute Stop.  In the Coal Age, that was done by an arrangement of sliding bars in a frame (the 'interlocking machine.')  More recently, electrical switches and devices replaced yard-long levers and brute force.  Today, the whole process is probably routed through a microprocessor.  In all cases, the object was (and still is) to make it physically impossible to route two trains through the same physical spot at the same time.

 

So, are there crossovers between multiple tracks, or to yard arrival/departure tracks, or a junction between routes?  That's an interlocking, and the signals will display AbsoluteStop unless there is a valid reason for them to display a different indication.  If any signal at that interlocking isn't displaying Absolute Stop, the switch points involved in the cleared route are locked.

In a complex interlocking it is possible to clear two (or more) non-conflicting routes at the same time.  For each route, the 'switch points locked when the signals are cleared' rule applies.

Chuck

[BaltACD]

Signal system relate the design preferences of those that built them or modified them over time.  No Class I's signal system was built as a 'whole cloth'.  Signal systems was installed as traffic and finances warranted,  a 100 miles here and 100 miles there, over time a entire route would be signaled....during the span of time required to signal a entire route a individual carrier may go through 2 or 3 Chief Signal Engineer's who each have their own design preferences as well as the suppliers of signal equipment are continually working on improvements to their products.  Needless to say, as the carriers install signals in formerly non-signaled territory they will install the most recent technology, and the technology that was installed on the first installation most likely will not be the same technology that is installed on the final installation.  Now since there were over 100 Class I carriers that have been folded into today's Class I carriers and the above scenario applied to each of those carriers as they installed their own signal systems, the complexity and quirks just grow and grow.

Today's class I carriers have embarked on projects to upgrade and renew their heritage signal systems to equipment of 21st Century technology in as much as much of the installed systems do not have redily available sources of repair parts and as requirements necessary to support the Positive Train Control mandate that is to be effective in 2015.

[BT CPSO 266]

I was at Altoona the other day and I could not help but notice something. Here is the situation for a westbound movement.

Ok, there is a Signal at ALTO and a signal at SLOPE (about a half mile apart) for governing the rail traffic. Now, I was waiting for about 30 min. and the signal position for for trains on #3 track was Approach @ SLOPE, however the signal position at ALTO for the same track is a Stop command. Now, the signal @ ALTO turned to a Proceed command, and a few minutes later a westbound freight comes by. After the train was gone, the signal at SLOPE went through the basic procedure and eventually reverted back to a proceed position, while the signal at ALTO remained a Stop command. 

I have also noticed that when there is a train following close enough to a westbound at ALTO the signal arrangement goes through more detailed commands, such as a restricting command. I have seen both of these kind of situations at other signaling bridges as well.

Another question, I was at Summerhill and the signals for eastbound trains are always turned on, but the signals for westbound trains turn on when a train is about a mile away, and turns off right after the end of the train passes under the signal bridge.

I hope I was specific enough. I thought of it may be for safety, but that does not make much sense when other signal bridges to not follow the same procedure. There may be something about this, but I lack sufficient information on signaling rules.