What is a “CP” (control point?), and why are they significant?
It’s a specified point on the railroad, often used as an endpoint when conferring track authority.
It can also be a location with plant controlled by a dispatcher (read “interlocking”).
Or both.
NORAC (10th Edition) specifically refers to my second “bullet”:
Sometimes they’re named (CP Smith), sometimes they use the milepost (CP293), mostly depending on the practices of the railroad in question.
I’m sure others will add more (or correct me).
CP or control point denotes a specific reference location on a railroad as noted in the official employee timetable and rules. It could be where there is a switch or turnout or other type of interlocking like beginning or end of double or multiple track operations. Or it could just be a reference point based on the beginning or end of block or the name of the block station itself. It is used as a reference for issuing instructions, referencing location, etc. Everyone knows the what and where of any given CP on the railroad because it controls every movement of every train, track car, directions, etc, around it. It may be based on milepost or by abbreviation for a location or a whole name. CP 2 would presumably be at milepost 2; CP BD could be the former telegraph code designation; CP HIgh could be at the top of a hill while CP Low could be at the bottom; CP NY could be New York; CP Nobody is made up by the EL and continues as a CP near Narrowsburg, NY today; Each is different and you have to know your timetable/book of rules for each railroad to know where each CP is and maybe even the reason it is so called.