[N&W] Re: APB signalling

nw-mailing-list at nwhs.org nw-mailing-list at nwhs.org
Tue May 18 22:32:36 EDT 2004

Manual Block - Remote Control was still in service between Hannibal and
Moberly in 1995 (and may still be in use today).  It had some drawbacks--
the train entering the siding had to throw the switch and because there were
no intermediate signals between the distant signals for the sidings, a follow-
up move would usually wait until a preceding train had cleared the next siding
(usually 12-15 miles) so they could proceed on a clear signal. It WAS an
improvement over time table and train order operation.  The Wabash people
preferred to refer to MBRC as "hermaphrodite CTC".
 >I learned that they were what the industry calls a system
 >of "Absolute Permissive Block" ("APB.")

    Call it what you want, but to N&W, it was and still is ABS or Automatic
Block Signals which have their own set of rules different from CTC. The
dispatcher did not control the signals or switches. At meeting points, trains
entering a siding the head brakeman would line the switch into the siding and
the rear brakeman, who better be fast or get left standing alone without a
train, would close the switch leaving the siding.  That is unless the train
holding the main line got there first in which case it's brakeman lined the
switch for the opposing train.
     Absolute Block is something completely different and required an official
at each end of the block to verify that the train had indeed cleared a block.
Used in CTC territory, all switches had to be spiked for the main line and
then trains could operate at track speed.
     One thing interesting, when the Punkin' Vine was finally operating
completely under CTC, Timetable 5 of May 20, 1973, was still in effect. This
was the last timetable showing a daily schedule for trains #57, #53, #50 and
#56. Even though trains were controlled by the Dispatcher and were governed
by CTC rules, these trains still could not pass stations before their
scheduled time. I have a few of these timetables if anyone is interested.
Jimmy Lisle

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