[N&W] Re: Signals

[nw-mailing-list at nwhs.org]

OK guys,

I think I understand the Automatic Block System signals, but the controlled 
signals are still confusing me.

First, just to verify ABS, these signals have only one arm. Each arm can 
display 3 aspects that I will call "v" for vertical, "d" for diagonal, and 
"h" for horizontal.

The interpretation of "v" is: "this block and the next one are clear, so 
proceed at maximum allowed speed".

The interpretation of "d" is: "this block is clear, but the next one is 
occupied, so reduce speed to medium and

be prepared to stop at the entrance to the next block".

The interpretation of "h" is: "this block is occupied, stop and then 
proceed at slow speed, prepared to stop for anything on the tracks". This 
interpretation of "h" is the reason the N&W system was referred to as 
"permissive"

Please, somebody yell at me vigorously if I've screwed up the above 'cause 
I want to get it right.

Now then, for the fun part. If you're coming up to a controlled switch, 
you're going to see a signal with two arms stacked vertically, and this is 
where I'm confused. A signal with two arms, each of which can assume three 
positions, ought to be able to display nine different aspects from "v" over 
"v" (which I will again shorten to v/v) through h/h.

If it were only desired/necessary to tell the engineer how fast to go 
through the switch, it looks like a one-armed, three position signal like 
the ABS signals would suffice. But I understand that the signal controller 
wanted/needed to be able to tell the engineer in some cases to "stop and 
stay stopped", so this requires at least one additional aspect for 
contolled signals. One way N&W did this was to put a single light below the 
arm of the signal.

Now, what I need help with is the use/interpretation of those other aspects 
of two-armed signals. What additional information was conveyed to the 
engineer? I'm going to present my guesswork/questions and hope that you 
guys will put me on the right track (ouch!)

When you come to a switch, you now have two possible routes by which to 
proceed, the one you've been following and one that "diverges" from it. 
Since my 1967 copy of N&W Operating Rules shows that the names of some 
two-armed aspects contain the word "diverging", I would guess that they 
convey some information about the diverging route. One possibility 
(probably too straight-forward to be correct) would be that the two arms 
convey the same type of information as the ABS signals for the two possible 
routes. The upper arm for the continuation of the present route, and the 
lower arm for the "diverging" route. The first problem I encounter with 
this interpretation is that in theory, all nine aspects would have meaning 
but the Operating Rules show only four aspects. For example they show no 
v/v aspect which in this scenario would indicate that both routes were 
clear for two blocks. It is also interesting to note that some of the rules 
themselves appear to be missing. Rules #284, 289 are not present, but

#282-A looks like it was stuck in as an after-thought. Is there any 
significance to this?

So what then is the real story? Another possibility would be that the lower 
arm would give the status of the switch and the upper arm would display ABS 
signal information for the selected route. For example, d/d would indicate 
that the switch was set for the diverging route and that the next block on 
the selected route was occupied. But again since there is no v/v aspect in 
the rules, you couldn't show "switch set to present route, next two blocks 
clear".

One other thought strikes me. Maybe it was against the rules to go through 
a switch at high speed and therefore some of the aspects could be eliminated.

Well, this has been a lot of speculation without much knowledge, but I hope 
it has served to show why/how I am confused and hopefully what can be said 
to clear things up for me (and perhaps others). Thanks for everybody's 
continued help and patience.

Jim Cochran