[N&W] CTC machine and signals

[nw-mailing-list at nwhs.org]

It seems Gordon Hamilton has done us a great service by putting the picture 
of the North Roanoke/Cloverdale CTC panel in the November/December issue of 
the Arrow.  The great thing about this is now we all have a copy of the 
same picture to look at to talk about signals, interlocking arrangement, 
and train control.  Furthermore, this panel is great because it controls 
only a fairly small and not too complex a section of the valley line.  And 
lastly, with magnification, you can read just about every label on the panel.

[Copy of picture is at: http://www.nwhs.org/qna/photos/1st_nw_ctc.jpg ]

I'm just starting to learn this stuff with the help of y'all and 
particularly Brother Pius The Maintainer.  But I'm going to start things 
off by trying to identify the parts and what they do.  I'm going to try to 
clearly mark all the places where I make assumptions and I hope you more 
knowledgeable folks out there will chime in with additional information and 
correct my blunders.

Let's start in the upper right-hand corner with the track schematic.  This 
area is labeled NORTH ROANOKE and shows two parallel tracks entering form 
the right and merging into a single track going to the left.  The first 
section of the upper track is labeled N B MAIN and there is an arrow to the 
left of this label pointing left.  I assume this indicates that this is the 
northbound main track of a two track main line and that schematically, 
northbound trains would normally use this track when moving from Roanoke to 
North Roanoke.  The line representing this section of track is broken at 
the position where the schematic symbol for the signal labeled L2 
appears.  I assume this break indicates the end of this block.  There is 
also a lamp lens smack dab in the middle of this section of track 
schematic, which I assume would light up to indicate the presence of a 
train in this block.  Would the light have been red?

Directly below the previously mentioned section of track is another one 
labeled S B MAIN.  Doesn't take a big stretch to assume that this is the 
southbound main track and that southbound trains would use this section of 
track when running from North Roanoke to Roanoke.  No pretty little light 
bulb here.  Is it because when a southbound train enters this block it is 
no longer under the control of the operator of this panel?

The next block to the left contains the schematic for a turnout labeled 
"1".  I'm going to refer to it as a "turnout" so as not to confuse it with 
those little levery things mounted on the panel down below the 
schematic.  I'm going to refer to those as "switches".  There is an 
indicator in the schematic for the turnout in the section that abuts the 
southbound main block.  I assume that it was used to indicate that any part 
of this block (either the part abutting the single track main block or the 
part abutting the northbound main block or the part abutting the southbound 
main block) was occupied and that this was all the information that the 
operator of this panel needed.  The final section of the schematic that I'm 
going to mention in this installment is the block immediately to the left 
of turnout 1.  I assume that this is a section of single-track main line on 
which trains run in both directions.  Two signals are shown for this 
block.  R2 would indicate to southbound trains approaching turnout 1 and 
L4L6 would indicate to northbound trains approaching the first turnout at 
Cloverdale.  I don't know how many miles of track this section of the 
schematic represents, but would/could this block have been composed of 
several blocks controlled by automatic block signaling?

As I said, that's as much of the track schematic as I want to bite off at 
present to keep the discussion very simple so that I might stand a chance 
of understanding it.  Now let's turn our attention to the controls mounted 
below this section of the track schematic on the panel.  The first "switch" 
mounted below the right-hand section of the schematic is labeled with a "1" 
in a circle which I believe corresponds to turnout 1 of the track 
schematic.  It seems to have two positions labeled N and R, which I assume 
are for Normal and Reverse.  Again I assume the normal position for a 
turnout is the "straight-through" configuration and the Reverse position is 
when it is configured to send a train on the diverging 
route.  Specifically, the case of our turnout 1, I assume that for a 
southbound train approaching the turnout, the normal position would send 
the train down the southbound main and the reverse position would send the 
train down the northbound main.  Something about the appearance of switch 1 
in the photograph leads me to think it may be something other than a simple 
two-position electrical switch, however.  Looking at the lever position 
closely, it appears to me to be in a position halfway between the N and the 
R positions.  I suspect that this switch in fact has momentary contact 
positions at N and R and its "at rest" position is as we see it in the 
photo straight up.  This could imply that when the operator desired to 
change the configuration of turnout 1, he would move the lever to either 
the N or the R position and hold it there until he received some positive 
indication that the turnout had assumed the desired configuration and then 
he would release the lever and allow it to return to its centered 
position.  This positive indication may have come in the form of one of the 
two indicator lights above the switch label plate illuminating.  I might 
imagine that if turnout 1 were in the reverse configuration the indicator 
light above the R might have been lit although I don't know what color the 
light would have been.  When the operator needed to change the turnout to 
the normal configuration, he might have rotated the lever from the centered 
position counterclockwise to the N position and held it there.  As the 
mechanism controlling turnout 1 (possibly pneumatic) moved the points, the 
light above the R would go out and then the light above the N would come on 
to indicate the turnout was in the desired configuration.  At this point 
the operator could release the lever and it would return to the centered 
position.

Now, lets talk about the switch labeled "SIGNAL 2" mounted just below the 
turnout switch.  It seems to be a three-position switch with three 
indicator lights corresponding to the three positions.  The lights over the 
L and R positions of the switch appear to be a different color from the 
light over the centered position.  The indicator over the centered position 
appears to be a lighter color and I might guess that it would be 
yellow/amber.  Now this is where I really start guessing and I'm hopeful 
someone knowledgeable will step in and shed some light on the situation, 
regardless of the color ;-)

Since there is a symbol for a two-arm signal labeled R2 on the track 
schematic that would indicate to a southbound train just before it entered 
the block containing turnout 1, I assume that the R position of switch 2 
would cause this signal to present a certain aspect to a southbound 
train.  I am purely speculating here, but I will assume that when the 
operator rotated switch two to the R position, he wanted to allow a 
southbound train to move toward Roanoke.  Likewise, I assume that when he 
rotated the switch to the L position it caused the signals labeled L2 in 
the track schematic to present an aspect that would allow a northbound 
train to proceed.  In the centered position, I would imagine that both 
signals would display their "most restrictive aspects"

Now I need help.  HELP!  What would the aspects have been that would have 
been displayed by signals R2 and L2 and under what traffic conditions?  The 
schematic signal for L2 seems to show one arm and a marker each for the 
northbound and southbound main lines.  The arm for the southbound main is 
represented as higher than that for the northbound main.  Is there any 
significance to this?  The only time I have seen different heights referred 
to was when signal controlling a main track and a siding were mounted 
together and the higher signal was for the main.  If only southbound trains 
ran on the southbound main, why was there a signal governing the southbound 
main in a position where it could only be viewed by a northbound 
train?  Since both of the arms had marker lights below them they could for 
sure display the "stop and stay" aspect which seems reasonable when you're 
heading into a single track main line.  What "proceed" aspect or aspects 
would they have displayed?  What aspects were displayed by the two arm 
signal R2?  Could it display "stop and stay" even though it doesn't appear 
that the schematic symbol for it shows a marker light?

So many questions, so few answers.  I hope this will spark a discussion 
that we can continue until we have a better understanding of how our 
favorite railroad used its signals to control its traffic.

Adthanksvance for not using terms like lamebrain and dummy in your 
responses, I really represent remarks like that.

Jim Cochran