[N&W] Re: Signals
nw-mailing-list at nwhs.org
nw-mailing-list at nwhs.org
Mon May 31 14:47:26 EDT 2004
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
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