Progressions Of NORAC Signals
Version 0.2 (August 08) -- Copyright © 2008 Deltareum. All rights reserved.
Comments welcome. Email George at deltareum (at) yahoo (dot) com.
First, a disclaimer: I do not have a Ph.D. degree in railroad engineering -- I am only a lowly locomotive engineer. The discussion that follows is based on what I have seen on the railroad. Caveat emptor.
By now, you must sense that signals work together. If a Stop Signal is coming down the line, there are signals that warn you about it. You will see those signals first, before you come aroung a bend and run straight into a Stop Signal staring at you. In the same way, if you need to get down to 15mph to go over a slow-speed switch, you will see a Slow Clear. Before it, though, you will see signals that bring you down in speed, so by the time you face the Slow Clear, you will be ready to come down to 15mph. Quite simple, isn't?
This sequence of signals is called signal progression.
Designers of signal systems on railroads use the signals that rulebooks give them, to help regulate the movement of trains. They assemble their signal progression to achieve optimum movements. You don't want to slow down a train too soon or too late. You want to allow the engineer to regulate his/her speed nicely and smoothly for the comfort of the passengers, but without delaying the train unnecessarily.
As a result, there can be many signal progressions. I've noticed that signal designers can be quite creative. I will show you the most standard signal progressions, and some more creative ones, but in your experience, you will see more on the railroad.
Signal progressions help you regulate the movement of your train. They help you anticipate things down the tracks and regulate your movement accordingly!
Progressions Leading To A Stop
The most obvious signal progression is an Approach, leading to a Stop Signal, or Stop and Proceed. You know this from the very indication of an Approach signal. As a progression, it looks like this:
Approach → Stop Signal or Stop And Proceed
Whether it is a Stop Signal or a Stop And Proceed depends on whether the next signal is an interlocking or automatic signal (or any special instructions regarding it).
If you have diverging approach signals, you would also expect a Stop Signal, or a Stop And Proceed to follow:
Medium Approach → Stop Signal or Stop And Proceed
Slow Approach → Stop Signal or Stop And Proceed
If an advance warning for a stop is needed, as in high speed territory, the designer would make aure an Advance Approach is shown, and the total signal proression for a stop would be:
Advance Approach → Approach → Stop Signal or Stop And Proceed
In this progression, the engineer will first see an Advance Approach, then an Approach, and finally a Stop Signal or a Stop And Proceed.
This is the basic progression for a stop. Some circumstances require more creativity. For example, if the location of the signal masts is such that the signal that shows Approach is too close to a Stop Signal for comfort, the designer may stick a Restricting inbetween, to bring you down in speed further:
Approach → Restricting → Stop Signal
I have also seen "slow-downer" signals used to warn of an Approach coming:
Approach Limited → Approach → Stop And Proceed
Such a progression is probably chosen for the designer's convenience. Maybe the designer wants to save in electronics that might flash the top yellow bulb to show Advance Approach and chooses an Approach Limited instead. Not orthodox, but it works.
However, you will never see the Approach replaced with any "slow-downer." The reason is simple: "Slow-downers" do not warn of an upcomig Stop Signal. Only Approach does that, and so it must be used in the progression.
If you can remember only one thing from this discussion, it is this:
After an Approach, or a Restricting, expect to see nothing better than a Stop Signal!
If you follow this rule, it will keep you from taking an unwanted 30-day, no-expenses-paid vacation.
Progressions For Slowing Down
Signal progressions that need to slow you down to a target speed can vary. The key idea is to smoothly slow you down to that target speed, not too soon, not too late, but just right. They, of course, depend on the target speed and the initial speed (track speed) themselves. The faster the track and the slower the target, the longer the progression.
The obvious "slow-downer" progressions are these:
Approach Limited → Limited Clear
Approach Medium → Medium Clear
Approach Slow → Slow Clear
These are pretty obvious: If you need to get to Limited Speed, an Approach Limited will get you to be down to Limited Speed by the time you pass the Limited Clear signal. Similarly for Medium and Slow Speeds.
So what happens in a 100mph territory if you need to get down to Slow Speed? The Approach Slow→ Slow Clear progression may not be enough, especially if the two signals are too close to each other. A longer progression will be needed to slow you down earlier.
In this spirit, you might have more complicated progressions, like these:
Approach Limited → Approach Medium → Medium Clear
Approach Limited → Approach Medium → Approach Slow → Slow Clear
and so on.
With "slow-downers" there is no end to creativity. I have seen Approach Medium → Approach Limited → Limited Clear, for example. Sometimes, weird progressions are the result of years of evolutionary history, where incremental changes in trackwork, speeds, and other factors, cause incremental changes to the signals themselves.
The lesson to take from these progressions is this:
Obey the target speeds indicated by each signal!
Thus, if you see an Approach Blabla, make sure you will be doing blabla speed by the time you hit the next signal. It will keep you from overspeeds (not to mention unwanted 30-day vacations) and your passengers from whiplash.
Combined Progressions NEW
Combined progressions are what happens when one progression leads to a certain signal, but another is needed to warn about the signal soon thereafter. For example, if a Medium Clear is needed to have the train go over a Medium Speed crossover, but then the train needs to come to a stop at the next signal, the Medium Clear progression and the Stop Signal progression can be combined.
The Medium Clear progression might be something like Approach Medium → Medium Clear, while the Stop Signal progression, by itself, might be Advanced Approach → Approach → Stop Signal. The two might be combined by first making sure that the Medium Clear now becomes Medium Approach. This would allow for the diverting speed at the crossover - Medium Speed - and warn of the upcoming Stop Signal.
The first signal in the progression, the Approach Medium, does not need to be modified. This signal will get the train down to Medium Speed and since the next signal will be Medium Approach, the train will reduce speed fast enough and the engineer will be warned of the Stop Signal coming up.
So the final progression becomes:
Approach Medium → Medium Approach → Stop Signal
This is a combined progression.
Incorrect Progressions NEW
Just as progressions are supposed to help you anticipate things and regulate your train accordingly, signals that you do not expect should raise red flags in your head. For example, after passing a Medium Clear, you would not expect to find the next signal to be a Stop Signal. You would expect to be forewarned about that Stop Signal with a proper combined progression, as discussed above. Since the Medium Clear does not warn of a stop coming up, the engineer is not expecting it. This is not a correct progression and normally should never show up.
Does it happen to see something like this? Yes, but only in cases of signal or other failure. It happened to an engineer on the Coastline, when the distant signal to East Matawan was Clear, and as he came around the curve, the home signal was a Stop Signal. The Cab Signals dropped at the same time he saw the Stop Signal. It was too late to come to a safe stop before the signal, but because of the incorrect "progression" he knew that the home signal had dropped in his face due to some failure. He stopped the train as soon as he could, but not before passing the Stop Signal, and he called the Dispatcher, who verified the signal failure. After getting permission to move from where he stood, he went on his merry way -- but with at least a couple of heartbeats missing.
Signs have progressions too. These should be obvious from the sign indications, but I list them here for completeness:
Approach Speed Limit Sign → Speed Limit Sign → Resume Speed Sign
Diverging Approach Speed Limit Sign → Speed Limit Sign → Resume Speed Sign
Approach Permanent Speed Limit Signs usually are not followed by Speed Limit Signs. They serve as mere reminders; you are supposed to know where the permanent speed restriction begins and ends, as they are just that: permanent.
Approach Sign → Stop Sign → Working Limits Resume Speed Sign
Diverging Approach Sign → Stop Sign → Working Limits Resume Speed Sign
If the employee in charge had replaced the Stop Sign with a Working Limits Speed Limit Sign, then:
Approach Sign → Working Limits Speed Limit Sign → Working Limits Resume Speed Sign
Diverging Approach Sign → Working Limits Speed Limit Sign → Working Limits Resume Speed Sign
When you see an Approach Sign, or a Diverging Approach Sign, always expect a Stop Sign to follow. The employee in charge may have replaced it with a Working Limits Speed Limit Sign, when he/she no longer needs you to stop and get permission, but you don't know that.
Finally, remember that a sign missing from those progressions does not relieve you from the responsibility of acting as if it were there: Your Bulletin Orders, TSRBs, or Form Ds tell you where the sign should be and you should know that.
Huh! And you thought you were going to get away without a pop quiz!
As I mentioned above, signal progressions help you anticipate and regulate. Remember that you should always anticipate the most restrictive signal. This way, you will never have any surprises. Surprises -- especially bad ones -- are the Engineer's worst enemy.
Here is a little quiz to help you anticipate properly.