Signal Question

[ulmer94]

Hello,

For you all that know these things:

There is a block signal on the UP line nearby where I live, where I have, in the past, seen it displaying clear for eastbound and approach for westbound for a single-track main line. Can anybody tell me if there is a reason for this, or is it a malfunctioning signal?

EDIT - While we're on the subject of signals, and this particular signal in particular, what is the single lamp yellow light under the main head of a block signal for? Looks like this, only the single lamp below is only for eastbound. It is not lit all the time, in fact it is hardly ever lit when I go by. http://media.photobucket.com/image/recent/Anfy_Boho/Sunset Route Double Tracking/IMG_9909.jpg

 

[RRSignal]

I assume you are talking about two signals - one for the eastbound and one for the westbound. I can't give you any conclusive data without knowing more about the area and while lies beyond those signals. I'd guess the eastbound (clear) has just mainline (automatic blocks) beyond it whereas the westbound signal has an interlocking ahead. Being a western road, they probably make use of Automatic Permission Block (APB) signalling as well. More about APB is here:

http://broadway.pennsyrr.com/Rail/Signal/Apb/

This is only a guess, based on what little info I have.

The single yellow light can mean either a restricting aspect or an advance approach aspect is to be displayed. Restricting is used on interlocking signals where one train can, for instance, follow another. Alternatively, they might use yellow-over-yellow in a 3-block arrangement to indicate when 2 blocks are free (3 clear blocks would generate a clear or green signal, one block the usual single yellow light for approach, red light for stop-and-proceed.) See here for more about aspects:

http://broadway.pennsyrr.com/Rail/Signal/aspects_us_cl.html

 

[ulmer94]

I assume you are talking about two signals - one for the eastbound and one for the westbound. I can't give you any conclusive data without knowing more about the area and while lies beyond those signals. I'd guess the eastbound (clear) has just mainline (automatic blocks) beyond it whereas the westbound signal has an interlocking ahead.

Actually, east of this signal, the next signal is a siding, west are automatic block signals. Like I said, it may have been malfunctioning, I haven't seen it displaying green one way and yellow the other in a while. Normally the signal is not lit when no trains are coming. I don't believe there were any trains nearby when I was seeing the odd, apparently conflicting aspects.

The single yellow light can mean either a restricting aspect or an advance approach aspect is to be displayed. Restricting is used on interlocking signals where one train can, for instance, follow another. Alternatively, they might use yellow-over-yellow in a 3-block arrangement to indicate when 2 blocks are free (3 clear blocks would generate a clear or green signal, one block the usual single yellow light for approach, red light for stop-and-proceed.)

I don't think it would be restricting because it's not an interlocking signal. Blinking yellow is used for advance approach, I see it on a fairly regular basis. When I saw the bottom lamp lit, though, the top light was solid yellow. And actually, that's the only time I can remember seeing the bottom light lit. Something to do with the siding, perhaps? I don't have a clue, I'm throwing stuff out there in hopes that someone will enlighten me what that little yellow light is for.