Early signaling on the N&W

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Tables appearing in the first few issues of “The Signal Engineer” show that
around 1910, approximately 95% N&W trackage was controlled by a manual
permissive block system with communications between block signal operators
being facilitated by telegraph.  I infer from this that at least in this
timeframe, block boundaries were, for the most part, coincident with
stations where the signal operator would manually set his signal for an
arriving train based his knowledge of the occupancy of the subsequent block
(whether he had admitted a previous train) and information from the
operator at the subsequent station as to whether the previous train(s) has
cleared the block.  If the operator knew the subsequent block to be
unoccupied, he would set his signal such that the arm was in the vertical
position (white light at night) indicating that the oncoming train could
proceed into the block at speed.  If the operator knew the subsequent block
to be occupied, he would set his signal such that the arm was in the
horizontal position (red light at night) indicating that the oncoming train
must not enter the block.  Under certain circumstances (of which I am not
totally clear), even if the operator knew the subsequent block to be
occupied, he could set his signal such that the arm was in the 45 degree
position (green light at night),  indicating that the oncoming train could
proceed into the block with the understanding that it was occupied and that
the following movement must be prepared to stop short of the preceding
train.  Since the N&W also used signal that could only display two aspects,
it is stated that the “permissive aspect” was achieved for these signals by
a flag (daytime) or a lantern (at night).  Was the flag/lantern placed on
the signal mast?   Was the flag/lantern colored green?  Other articles in
these magazines indicate that there was an effort to push the adoption of
green for clear and yellow for caution as well as to move to
three-position, upper quadrant signals, but I don’t know when the N&W may
have made these changes.

If any of you “signal heads” out there have additional information/insight
please share it with us.

Jim Cochran
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