Signals (and Numbers of Bulbs)

Hello all, I have a question that I really wanted to have answered for a long tima dn I thought this would be the best place to ask it:

I was wondering for American railroads what signals are placed in what conditions and how are the number of heads and bulbs per head determined for that signal?

I am mainly referring to signals with different lights for different colors so not searchlight signals.

I have seen signals with (per head) 3 bulbs, one bulb, 3 bulbs; and 3 bulbs over 3 bulbs, etc.

I have a basic understanding that 1 headed signals are just used for a block, 2 headed for junction or basic crossovers, and 3 headed for interlocking (i could be wrong).

But I am confused as to how each head is configured, the top head may have 3 bulbs, and the bottom 1 or something so it all depends I guess and I would like to know how those choices are made as to how to make the signal for that particular place.

Like here there is a good amount in diversification between bulbs per head (and also the middle heads here both have 4 bulbs which I question too?) :
http://www.railpictures.net/viewphoto.p ... 404&nseq=9


Any help would be greatly appreciated this is kind of the only place I can really hope to get a good answer with so many knowledgeable minds on the railroads.

Thanks

Davis

Whatever aspects the signal needs to display determined how many lamps (not bulbs) are fitted. Any signal, automatic or controlled, can have 1, 2 or 3 heads. Just review any railroad signal aspect chart and you can see the 20 or so types of signal indications that can be displayed. Each has a specific use case. When the use case is encountered the signal must have sufficient lamps to display the signal indication, simple as that.

But I am confused as to how each head is configured, the top head may have 3 bulbs, and the bottom 1 or something so it all depends I guess and I would like to know how those choices are made as to how to make the signal for that particular place.

It all depends on the track layout and the various movements the trains are able to make. It is hard to answer this question unless you yourself first go and review the signal aspect chart for the railroad you are interested in. If you have absolutely no experience with the signal aspects at all start here.

Like here there is a good amount in diversification between bulbs per head (and also the middle heads here both have 4 bulbs which I question too?) :
http://www.railpictures.net/viewphoto.p ... 404&nseq=9

I'll explain this one example, but you need to do some of your own research first and then come back with more specific questions. I would urge others here not to launch into a signal primer because they do exist other places.

Those are the new CSX darth vader type signals at Point of Rocks and have a full compliment of lamps in current CSX practice (3-4-3). The junction at Point of Rocks is a wye with an interlocking at each point of the wye. This meas you not only have short distances between signals, but also back to back junction signals. This means that the signals needs to display Slow Approach for a short distance stop at the next signal, but also combination signals like Medium Approach Medium for back to back diverging paths. The 4th lamp in the middle head is for a Lunar White restricting aspect which CSX prefers to using a bottom yellow lamp. Here is a list of every lamp and what signals it is used for. I'm assuming medium speed turnouts.

Top head:

Green - Clear
Yellow - Approach, Approach Medium
Red - Stop, Medium Clear, Medium Approach Medium, Slow Approach, Restricting

Middle Head

Green - Medium Clear, Approach Medium
Yellow - Medium Approach Medium
Lunar - Restricting
Red - Clear, Approach, Slow Approach, Stop

Bottom Head

Green - Medium Approach Medium
Yellow - Slow Approach
Red - Clear, Approach, Medium Clear, Approach Medium, Restricting, Stop

Thanks Mike for the explanations!

I have been trying to do some of my own research on it but it seems what really clicks for me is looking at charts and comparing the "situation" to the possible signal aspects.

What I really am not grasping is how to relate a specifc interlocking track setup to interlocking signal indications. I know how signal indications are displayed (and when I doubt I can check my NORAC book) but I am sturggling to put a specifc aspect to a track setup.

I can get the basics like with single headed dwarf signals you would only get Slow Clear, Slow Approach, (and possibly Restriciting and Stop and Proceed) but otherwise I am basically lost.

Here is my general understanding of how the basics work (and please correct me where I am mistaken:

If it is just a block with no switches or anything you have a 1 Headed Signal.
If there is only one switch to possibly take (crossover) then you have a 2 Headed Signal.
If there is more than one switch (an interlocking) then you have a 3 Headed Signal.

Then some of these special ones I do not get:

If you have a single track going double the single track has a 3 Headed and the two double tracks have 2 Headed Signals.

If you have a crossover and the next signal is a 2 or 3 Head then you have a 3 Head.



Please help me out, I know it can get frustrating trying to explain this but it gets very complicated for me.

Thank you so much for your time Mike, you have been a continued help.

Davis

Davis - I found the the page here extremely useful:

http://www.alkrug.vcn.com/rrfacts/signals/signals.htm

The author - an engineer on the BNSF - has done a magnificent job diagramming and describing the various signal aspects, their meanings and how to quickly "decode" them.

Recommend making a hard copy of the entire article (it's a good 10+ pages long). Then spend a while studying it - it should answer all your questions.

...FB

If it is just a block with no switches or anything you have a 1 Headed Signal.
If there is only one switch to possibly take (crossover) then you have a 2 Headed Signal.
If there is more than one switch (an interlocking) then you have a 3 Headed Signal.

No, those are not good assumptions to make. I know block signals with 2 or 3 heads and interlocking signals with multiple routes with only 2 or sometimes 1 head. This is speed signaling, not route signaling. The number of signal heads is dependent on which routes are available to a train at an interlocking and how a train's speed must be controlled at an intermediate block.

Why does this CPL at the entrance to a double track segment lack a medium speed orbital? Because its an equilateral turnout where both routes are at Normal speed.

If you have a single track going double the single track has a 3 Headed and the two double tracks have 2 Headed Signals.

Some railroads preferred to have a 3rd head for their Restricting aspects as R/R/Y was seen as safer to R/Y. Also the home signal could be the distant signal to another signal requiring a Approach Slow aspect. There could also be a short stopping distance requiring the use of Slow Approach.

If you have a crossover and the next signal is a 2 or 3 Head then you have a 3 Head.

That's not always true, but can be where stopping distances are short or Approach Slow is needed. Before flashing relays became common the third head was needed for Medium Approach on some railroads.

The author - an engineer on the BNSF - has done a magnificent job diagramming and describing the various signal aspects, their meanings and how to quickly "decode" them.

That article has a few errors. Look at the description of Approach Medium and Approach Slow. Neither of those two guarantees a Clear block after the diverge.

I find the darth vadar style signals easy to mess up compared to the PRR and B&O signals. Most people instinctively know a horizontal line means stop, a vertical line means go, and a slanted line means caution. Now the lunars can get confusing, but the basic signal head has an intuitive shape.

Okay so I understand that the more heads and bulbs are to represent indications that represent speeds.

But how just by looking at tracks can you tell what the signal looks like. Like looking at this signal bridge here:
http://www.multimap.com/maps/?qs=alexan ... alexandria, va|Alexandria, Virginia, United States

You can see that the signals are facing West on the gantry but from here is there anyway that you can look at the trackwork and determine what the signals are setup like? This I would really love to know how to do.

Thanks

Davis

strench707 wrote:Okay so I understand that the more heads and bulbs are to represent indications that represent speeds.

Generally ... Each railroad has it's own preferences as to how it wants their signals to look. Consistency is nice.

But how just by looking at tracks can you tell what the signal looks like. Like looking at this signal bridge here:
http://www.multimap.com/maps/?qs=alexan ... alexandria, va|Alexandria, Virginia, United States

You can see that the signals are facing West on the gantry but from here is there anyway that you can look at the trackwork and determine what the signals are setup like? This I would really love to know how to do.

My magnifying glass is not good enough to see much of that signal. It would take a lot of research on that specific railroad to know what the preferences of their signal department.

What I have done for the roads I care about is get as much information as possible on those roads ... Employee Time Tables may be available depending on road. Signal aspects for that particular road will be included. Then I looked (without trespassing) at the actual signals on the line. I took note of the number of heads and what lamps were present. Then I sat down, ran through the signal aspect tables for each signal and eliminated the impossible. After a while I picked up their patterns. Now I'm pretty good at estimating what a signal should look like.

But even after that study there were some stumpers ... a diverging route with only a red lamp on the bottom of two heads. Fortunately there are scheduled trains so I simply made sure I was present when one used the diverging route and found that the railroad used a flashing red "restricting" aspect for that move. This observation also cleared up a couple of other places where my guess would have been wrong.

If you're trying to be an expert on one line it will take some time focused on that one line --- the more lines you want to become an expert on the more time it will take. Fortunately the roads I care about the most have simple signals - but I've still seen a few things that required a trip back to a rules manual to figure out what I saw.

Well would a railroad's signal policy (that was CSX I linked in Northern Va.) be consistent or would each subdivision have its own little patterns normally? Obviously some railroads use searchlights, some have heritage signals (i.e. CPL's) and some have the Vader kind but does CSX have a way they tend to do things?

Thanks

Davis

I would not expect consistency across an entire large company ... too many old lines that never got "new" signals. Consistent within a subdivision? Probably. Again, it depends on where they got the lines and if they spent the money to change the signaling system.

There is no simple answer ... you have to do the footwork yourself. The more lines you want to know the more lines you need to study.

Okay thanks guys for all of the help! I shouldn't have expected simplicity and consisitency in an already complex system across an entire nation, that was a little much! I actually enjoy going on those little missions though to find out stuff.

Thanks again

Davis

Thank you very much! I liked the link and it is very informative. Do you have any idea where I could find modern charts of this area?

Thanks

Davis