General Discussion

Ok, I've drawn the whole 'block'.  I have included what I would have guessed as the signals in the area.  RR East of the block there is a diamond (2 blocks away) and RR West of the block is double track for a while (many blocks).

If the tracks are bidirectional, seems to me there should be a signal between 4 and 7 facing 'east'. 

Art 

Art's right about that.

I also have a problem with "advance approach" being a default indication for anything here. These are all absolute signals at control points, hence the default is "Stop". I'd need more information about the surrounding signals (blocks away) to know why "Advance Approach" is needed at all.

If you have an entire block between the end points of the siding, you'd probably also want block signals on the other track, even if there are no switches involving that track.

 Yeah, Art's right.   You need an east facing signal between 4 and 7.   The default indication of any controlled signal is STOP.

Advance Approach is used where the blocks are short, and you need more warning time before encountering a STOP.   It should be noted that not all roads use Advance Approach, instead preferring to use two Approaches.

Carl's got a point too.  Depending on the distance between 4 and 7, there may be one or more Automatic Block signals between them.  In this instance, the siding is probably not signaled other then the entrance and exit signals. 

Nick

CNW 6000:

On the 3 headed signal (#1) top signal controls the 'main'...would the 2nd one control the siding or the crossover?

None of the heads "control" a particular track, other than they all "control" whatever track is beyond the signal.

The combinations of signals form an aspect and the different aspects have indications, which are the instructions for what that combination tells you to do.

So if the siding is bonded and the signal displays red over yellow you could be either going through the crossover or going into the siding.  The non-red signal not being at the top indicates a diverging signal, not which track.  If it was tied to which track then at every crossover on a 4 track main you would need 4 heads.

This should be what would be correct then.  I don't think the distance between '4' and '7' warrants an intermediate but I'll check.

Let's say, for example, that a train is lined through on Main 2 (routed 1-4-8)...how far ahead of the train would the signal change?  Once they enter the block past the diamonds (remember they're RR East of here) or a different point?

Couldn't tell you about eastern railways, but no Class 1 western railway signal engineering department would approve this.  Changes I would need to make are:

1. Signal 3 single-head only (what's the second head for?)
2. Need an intermediate on Main #2 facing both directions perpendicular to the location of signal 8
3. Distance between signals 2&5 and 1&4 cannot be more than about 2,000 feet.  Either move the siding turnout back to the CP for the crossovers, or move the crossovers to the siding turnout.  Big CPs = big money and loss of train capacity.
   
4. Signal #3 may need to line up with #4 and #5 if there is any chance of confusion that an aspect on signal 4 applies to the siding. 
   
5. You will need to have 20' track centers between siding and main #1, or use cantilevers for signals 4 and 7. 
6. Not understanding why you have three-head signal at #1.  Even if you have different turnout speeds in the crossover and the siding switch.  I can get every aspect I need to do my aspect charts with only two heads.
   

RWM

Railway Man:

Couldn't tell you about eastern railways, but no Class 1 western railway signal engineering department would approve this.  Changes I would need to make are:

1. Signal 3 single-head only (what's the second head for?)
2. Need an intermediate on Main #2 facing both directions perpendicular to the location of signal 8
3. Distance between signals 2&5 and 1&4 cannot be more than about 2,000 feet.  Either move the siding turnout back to the CP for the crossovers, or move the crossovers to the siding turnout.  Big CPs = big money and loss of train capacity.
   
4. Signal #3 may need to line up with #4 and #5 if there is any chance of confusion that an aspect on signal 4 applies to the siding. 
   
5. You will need to have 20' track centers between siding and main #1, or use cantilevers for signals 4 and 7. 
6. Not understanding why you have three-head signal at #1.  Even if you have different turnout speeds in the crossover and the siding switch.  I can get every aspect I need to do my aspect charts with only two heads.  Upper head needs to have
   

RWM

1.  If #3 is a single head, what about #6?
2.  Why there?
3.  The siding could move (theoretically) and one of the crossovers could be eliminated as the next block RR West has exactly the same capacity.  Would it make sense to eliminate that?
4.  Makes sense.
5.  Cantilevers makes sense for those signals.
6.  Can you clarify the 'aspect' part?  I'm a tad confused.

This is a hugely helpful discussion on signalling and signal locations, something I've always been fascinated with.

Let's say I was able to magically redraw the configuration as below.  What changes?

Now this guy knows his stuff, Brian!

1. Correct--#6 would be a single head as well.

2. Basically, between 4 and 7 constitutes a block. You'd want a block of similar length on the other track.

3. Whether you move the siding switch to one side or the other of the crossover (and eliminate the other crossover) depends on the versatility you want to build in. RWM is just suggesting that the siding switch be directly next to the easternmost crossing switch on the other track, to shorten the distance between 1/4 and 2/5.

6. Every signal you see has four major references:

--the rule number

--the name ("Clear", "Approach", etc.)

--the aspect (the way the signal appears--such as green-over-red, flashing-red-over-red, etc.)

--the indication (that the first three mean--proceed at normal speed, proceed prepared to stop short of next signal..., etc.)

Now Signal 1 on the old diagram would show lineups for all three routes with two heads:

--1 to 4: Clear would be green over red.

--1 to 5: Diverging Clear: red over green.

--1 to 3: Restricting--red over flashing red.

Approach signals would substitute yellows for the greens in the aspects, and the word "Approach" for "clear" in the names. And, of course, a stop indication would be red-over-red. At least in theory, any time the route into the siding was selected (and the control point itself is clear), you'd get the Restricting signal, because that requires you to stop short of anything you may encounter in the siding.

Now, to your revised diagram:

Signal 3 would still need only one head. It just lets you out of the siding, and you're governed by your observation of the lineup (and proceeding prepared to stop short) until your train has cleared the control point. Or to the next block signal, as I mentioned in previous responses.

RWM's Comment 2 still applies.

Are things getting clearer?

I was waiting to see if RWM would 'weigh in' on this . . .

Couple of observations and questions -

As a signaling 'Knows-Next-to-Nothing', most of these posts seem to me to be just conclusions = 'Do it this way', without a lot of rhyme or reason stated behind them. 

So I'm curious if someone could explain the principles, rationale, process, or reasoning that is used to figure out where the signals go, what aspects they should be able to display, how many heads they will then need, etc.  Otherwise, I fear I'll have to figure it out indirectly by inference / osmosis = 'They did it that way, most likely for this reason or to achieve that result or effect'', etc.

Also - I didn't see where a maximum authorized speed was stated or postulated.  Would the signal layouts and indications at this location be much different if it was in an downtown urban area, where the maximum speed could realistically be 30 MPH or less, or out on the high plains in 79 MPH territory ?

Still, it is kind of a fascinating insight into the 'from scratch' design process' for these kinds of systems.  Thanks to all who have contributed. 

- Paul North.

 You're correct, I meant to type in that #6 only needed a single head as well.

 As for your track configuration, I don't know what your track is intended to do, so tough for me to comment.  The only think that's obvious is that the outside siding can enter Main #1 either universal (facing-point) in respect to the crossover, or lapped.  If the point of the outside siding is to serve both main tracks for salting away a train, bad-order setout, or maintenance-of-way setout, then you probably want it to be universal (as you have it in the drawing above).  If the point of it is to act as a third-main track for meet and pass events, then you probably want it to be lapped.  The thing to think about is that with a universal crossover, the moment any train crosses over then the whole interlocking is tied up and only one train at a time can use it -- the train that is crossing over.  All other trains come to a stop.  With a lap crossover, two trains can use the interlocking simultaneously.  Because trains have length, and have effects on signal aspects for a great distance ahead and behind, the ability to have two trains use the interlocking simultaneously can add a great deal of capacity. 

 Here's how this works.  With a lap crossover at both ends of the outside siding, any of the tracks can act as a siding.  You could, for example, stop a slow eastbound ttrain between switches on Main #2, and run around it with a fast train on Main #1.  It takes the crossover at the west end, and travels east on Main #2 to the crossover at the east end, and returns to Main #1.  The overtaken train can leave immediately after the faster train passes the next intermediate.  Meanwhile a westbound train can use the outside siding to make room on Main #1 for the fast eastbound train.

RWM

Paul_D_North_Jr:

I didn't see where a maximum authorized speed was stated or postulated.  Would the signal layouts and indications at this location be much different if it was in an downtown urban area, where the maximum speed could realistically be 30 MPH or less, or out on the high plains in 79 MPH territory ?

Paul, the signals wouldn't change much. You would expect that in higher-speed territory the crossovers would be good for higher speeds (hence they would be longer between end points), just because you wouldn't want too marked a slowdown for a crossover move followed by a restoration to maximum speed. That's just too inefficient. In a higher-speed environment, your blocks would be longer. If you still had a short siding, that might call for shorter blocks, and an Advance Approach indication might be called for--or not, as mentioned in a previous post.

signal 1-2 are 2 headed signals and 3 is a single signal as is 6. move 4 down to the west end of the siding where 8 is and move 5 to the west of the diamond both would be 2 headed signals no need for 8. 7 is perfect and a 2 headed signal

If I've come to one conclusion here, it's that there is no single right answer.  That we are down to the few major railroads that we are has actually simplified things, methinks, since in the day I'm sure there were a significant variety of signal practices by the various RRs. 

tree68:

If I've come to one conclusion here, it's that there is no single right answer.  That we are down to the few major railroads that we are has actually simplified things, methinks, since in the day I'm sure there were a significant variety of signal practices by the various RRs. 

 

The variations are trivial -- any good signal engineer can work for one Class 1 this morning and another this afternoon and get it right.  The engineers I've employed have worked for SP, UP, CSX, L&N, BN, BNSF, SS, C&O, Amtrak, Santa Fe, and probably some others I've forgotten about.  We all managed to get along and get it done without any problems.  The principles have been around for more than a century.  Get a rule book, get a signal practices manual for that railroad, put them on your desk, and that's all you need.  That's why when railfans obsess about the EXTREME DANGER of signal aspects being different from one railroad to the next I just roll my eyes.  If signalmen can figure it out, so can anyone in the operating department and the track forces.

RWM