B&O CPLs

[Eboy87]

Hi all. I’m working on a route that follows a fictional ex-CSX (B&O) line from the DC-Baltimore area up into the mountains. What I’m curious about is the D on the B&O CPL signals. I believe I read they stood for Delay In Block, or distant, depending on what guide you use.


I understand the delayed in block rule being that if a train stops in the block, it must proceed at a prescribed speed until it can make out the next signal. An example being, train A enters the block on a clear aspect, makes a stop, proceeds cautiously as train B may have knocked the next signal down to an approach or even stop in the time train A has been stopped.


What I’m curious about is the application on signals on the railroad. I’ve seen photos of the automatic signals in Gaithersburg, MD where one set of signals has the D plates, while the other side doesn’t. Does this mean they’re simply repeating the aspect of the next absolute signal, or is there another meaning to putting that sign on them?


Or am I confusing two different rules here (which is entirely possible)?

 

[RRSignal]

Hi all. I’m working on a route that follows a fictional ex-CSX (B&O) line from the DC-Baltimore area up into the mountains. What I’m curious about is the D on the B&O CPL signals. I believe I read they stood for Delay In Block, or distant, depending on what guide you use.


I understand the delayed in block rule being that if a train stops in the block, it must proceed at a prescribed speed until it can make out the next signal. An example being, train A enters the block on a clear aspect, makes a stop, proceeds cautiously as train B may have knocked the next signal down to an approach or even stop in the time train A has been stopped.


What I’m curious about is the application on signals on the railroad. I’ve seen photos of the automatic signals in Gaithersburg, MD where one set of signals has the D plates, while the other side doesn’t. Does this mean they’re simply repeating the aspect of the next absolute signal, or is there another meaning to putting that sign on them?


Or am I confusing two different rules here (which is entirely possible)?

It sounds like you may be confusing things. Distant signals are placed in advance of home (interlocking) signals and give you an idea of what the indication will be at the interlocking, so you know what's going to happen e.g. if you're going to divert, if you're going to proceed straight ahead and at what speed, etc.

Delay-in-block is used between a distant signal and a home signal to remind the train engineer to proceed prepared to stop at the next signal until he can see it clearly and only if he's made a station stop or slowed down to 10mph or less. Under NORAC, after stopping at a station, a push-pull passenger train can accelerate up to 40mph until seeing the home signal and getting a clear or higher-speed indication; all other trains (including passenger trains that stop for some other reason than a station stop) have to operate at restricted speed. Simply put, the DIB rule arose out of the Silver Spring, MD accident, in which an engineer forgot the approach signal he received before stopping at a station, proceeding at full speed into an occupied interlocking.

 

[Eboy87]

That's what I thought. So essentially, the D plate is added to signals as just a visual reminder of the DIB rule. If so, does anyone know whether this applies to only territory with push-pull operations, or would it be applied anywhere? I don't think I've seen any photos outside of commuter rail territory that has the plates attached to CPLs.

 

[RRSignal]

I can't comment specifically on CPLs or the relevant territories, but I believe they are used anywhere passenger trains run. Looking at some older SEPTA charts (before they wrecked the system with PTC) I see DIB signs in territories that wouldn't normally feature push-pull trains. Mind you, SEPTA doesn't have very many (8); the vast majority of the fleet are EMUs.

When you look at the rule in context of what happened and why it was created, it makes sense.