As has been said several times, a control point is a controled signal (per GCOR and Norac definitions).
The reason you have controled signals is you want to control trains operating over switches or on different routes. So yes there will commonly be switches associated with a CP and where there are switches there will be multiple routes.
CP’s come in all sorts of shapes and sizes and histories of how they got there. There is no one simple description that covers every option in detail. In the modern era the line between CTC-CP-Interlocking gets blurred somewhat. Prior to the 1980’s the term CP wasn’t used, CTC and interlockings had different rules (very similar but with some differences).
if you were adding CTC/signals to your layout, how would you identify the CPs? or is it more about defining the interlocking logic that the CTC system uses to determine the signal indication based on actual switch position, CTC signal lever setting and block occupancy of associated trackage?
Reading archived accident reports from the NTSB, there’s always a mention of the last control point. They are always listed as manned, or open. Most read like " train xxxx past so and so interlocking tower which is the last manned control point." Or " train xxx passed through signal xxx which is the last open control point."
While these examples come from steam era reports, one has to assume that control points were manned stations, towers, or platforms where train orders, and signals were given to direct train movements over a section of the railroad. Either a block, branch, yard, or station. I could not find the glossary of terms or definitions on the NTSB’s website.
Be careful with eras here. In the steam era, CTC (rule 261) was not as common as it is today, and “control points” were not defined in railroad rule books.
One also needs to remember that there won’t be any “steam era” NTSB reports since it wasn’t created until 1967, well after the steam era. Any truly steam era reports on accidents would probably be ICC reports.
One also has to remember that the signal and control systems, the actual design, operation and, maybe most importantly, communication systems were vastly different in the steam era than in a more modern era, so the concept, definition and function of a control point might be different.
You are kinda going backwards. A control POINT is a location. Its the signal equivalent of a STATION.
Orville could be just one CP.
Once again, don’t read more into a CP than is there. There are all the rules and operational considerations for interlockings and for CTC. There are NO “CP rules”. Don’t attribute stuff that is a CTC, interlocking or general signal design thing to a “CP”. A CP is designated to identify a group of locgically and operationally connected switches and signals.
In my defense. I know the ICC investigations is no more. I found the archives from the NTSB web site. From 1911 through 1965. There is some good reading in the reports and one can spend an entire night just skipping through. I don’t know if it’s the NTSB or the National archives that maintains the list. I believe it is the National archives. It could be the DOT even. Whoever maintains the list I found it through the NTSB’s website.
No. A CP is “the location of absolute signals controlled by a control operator.” (GCOR 2010).
There is no requirement for switches, there is no requirement for a “tower”. There could be, but there doesn’t have to be. Probably 90-95% of all the CP’s are just one end of a siding. No towers, just one switch.
The KEY is that there is a location with a manually controlled signal or signals (see GCOR). There can be lots of other stuff, but what defines it is there is the manually controlled signal.
An interlocking may be a CP or it may not.
A CP can be in CTC or it may not.
That’s why I keep saying don’t read more into a CP than is there.
As far as Orville goes, the diagram is for an interlocking, in pre-CP daysof the PRR. To see what would have been done vis a vis CP’s, just find a timetable for CR or whatever railroad now operates it and see what they did. It could be one CP or it could be 4 CP’s. If one route went to the NS and the other to the CSXT it could be one CP on one railroad and 3 CP’s on the other or it could be one CP on each railroad.
In the 200 miles between Dexter, MO and N Little Rock, AR on the UP there are 49 CP’s at 37 stations and zero “towers” There is one interlocking, but its not a CP and there are 8 stations that don’t have a CP associated with them.
A CP is “the location of absolute signals controlled by a control operator.” (GCOR 2010). A milepost won’t have controled signals.
If you are modeling pre-1985 or so then CP’s weren’t defined in the rules. If you are modeling post-1985 or so, they were. If you are modeling pre-1985 then no.
The CTC will be essentially EXACTLY the same in either case. If you are modeling pre-1985 then the interlocking at Birdsboro would be called the interlocking at Birdsboro and would be manually operated by a tower at Birdsboro, then later an operator in the Tower at Oley, then eventually post 1985 would be CP Bird. The signal system would work exactly the same in any case (except maybe the controls would be located in different locations and type of control might have been upgraded or changes in the rules over time) for the trackage that was common in the various eras.
Take the switch at the east end of the siding at Bess near MP 25, which is in CTC.
Pre-1985 it would be called the “east switch at Bess”. The would be an eastward signal on the main, there would be a westward signal on the main and a signal to come out of the siding. A dispatcher or operator would control the signal (and switch). It would not be an interlocking.
I think CPs are generally named after nearby mileposts. On MetroNorth, the Hudson line CPs are named after the mileposts, on the Harlem Division they add a 1 in front of the milage figure, and on the New Haven line they add a 2 in front of the milage.
Simply put, a control point is any signal that is controlled by the dispatcher. A CP is a STOP signal. If the signal displays STOP, you must get permission from the dispatcher to pass it while it is displaying the STOP indication. A CP has a name.
Signals with numbers are “Intermediate” signals. These signals display “Restricting” as its most restrictive aspect. Meaning a train can pass the signal at restricted speed without having to contact the dispatcher. They are not controlled by the dispatcher. Instead, they are controlled by the signal system. When the dispatcher sets up a “current of traffic” by lining up the Control Point, the aspect of intermediate signals will follow accordingly.
If the dispatcher has not set up a current of traffic, intermediate signals between two control points will show aspects indicating the condition of the block ahead. This could mean that with enough signals between two control points, you could go out into the field and see a set of signals side by side displaying “Clear” in both directions. Once a current of traffic is set up, the opposite signal will go to a restricting aspect.
One other thing to keep in mind and this is very important, the dispatcher CANNOT and DOES NOT give a train a Clear signal. The dispatcher has no idea what aspect is displayed to the train crew. The “SIGNAL SYSTEM” is what provides the aspect shown according to the track conditions ahead! The dispatcher can only tell the signal system what he wants done.
No. The key word in “control[led] point” is “control”.
It’s a location where the dispatcher controls signals (and usually turnouts, but an CP can have zero turnouts) in order to control train movements in CTC. Turnouts and signals will be interlocked to prevent conflicts.
If there’s nothing there to control, it’s definitionally NOT a control point.
I have always considered a ‘control point’ to be a location on a ROUTE where train position is determined and permission to proceed further given.
It is not material what type of equipment is used to convey that authority; the ‘point’ is spatial.
How CPs are practically implemented would, of course, vary by railroad, and there is a variety of ‘safe’ options to determine exactly where on a given railroad or route the “functionality would be implemented”. But arguing about the size or predilection of the angels dancing on a particular pinhead does not determine why the pin is there in the first place.
Well, yeah, it is. CTC control points (dispatcher controlled signals) are where the dispatcher controls the signals to give the trains their permission to proceed.
I’m not sure how you’d argue that it’s NOT a location where permission to proceed further is given. It’s absolutely the point where a train will stop if it doesn’t have permission/signal indications to go further.
