Question: I’ve been noticing the term “control points” (CPs) being used in train-watching videos and in your magazine. The article on John Schindler’s amazing St. Louis Junction [March 2020] mentions CPs including West Madison, Gratiot, and Chicago Throat. Canadian Pacific’s Paynesville Sub has CP 115 and CP 70. This tells me CPs can be designated with numbers corresponding to mile posts as well as locations. What exactly are control points? Are these areas where signals, defect detectors, and crossovers are located? – James Radde, Bloomington, Minn.
Answer: Under Centralized Traffic Control (CTC), the dispatcher directly controls the movement of trains with absolute signals and remote-controlled switches. A control point is a signaled interlocking controlled by a dispatcher in CTC territory. Most switches in a CTC interlocking can also be controlled from trackside, though doing so still requires the permission of the dispatcher. The signals at CPs let the engineers know when they have permission to occupy the track ahead, as each section of track between two control points is normally occupied by only one train at a time.
A control point is a controlled signal by itself. The presence of a dual-control switch, movable-point front, or other remotely controlled device does not constitute a control point.
A further point of emphasis to your sentence reading “The signals at CPs let the engineers know when they have permission to occupy the track ahead, as each section of track between two control points is normally occupied by only one train at a time” is that a “controlled signal displaying a proceed indication confers AUTHORITY (not “permission”) for movement to the next controlled signal.
Further, multiple movements in the same direction may be authorized by controlled signal indication between control points. Movements are limited only by track occupancy conditions displayed by controlled signals and intermediate automatic block signals.
Definitions contained within a rule book are crucial to understanding applicable rules pertinent to operation within limits of CTC and explanations of both definitions and applicable rules will require time and column inches not necessarily available in this format.
In the first paragraph of my statement above, I created a typo that I cannot edit: I used the term “movable point front” and intended to state “movable point frog”. Be governed accordingly.