From: ahk@chinet.com   
      
   Robert Heller   wrote:   
   >At Sat, 2 Jan 2016 16:10:36 -0600 Stephen Sprunk  wrote:   
   >   
   >>   
   >> On 02-Jan-16 14:48, Adam H. Kerman wrote:   
   >> > Stephen Sprunk  wrote:   
   >> >> On 02-Jan-16 01:46, spsfman wrote:   
   >> >>> It isn't for a grade crossing, but it quite possibly could be for   
   >> >>> a diverging track. The tracks are elevated and grade separated   
   >> >>> where I saw the signal. But just ahead, the tracks go to grade   
   >> >>> and pass the now being completed maintenance yard. While the yard   
   >> >>> is on the left, I think there is also a siding on the right in   
   >> >>> the vicinity and just past the yards. So it rather makes sense.   
   >> >>   
   >> >> Sounds like this is coming west from Expo/Bundy Station; the yard   
   >> >> is on the left after the line returns to grade, but according to   
   >> >> the FEIR, the two mains are on the far right and the only siding (a   
   >> >> yard lead, plus the yard itself) is on the left.  I don't see   
   >> >> anything in the plans that would indicate a crossover or other   
   >> >> interlocking involvement on the right track, but since the left   
   >> >> track does and thus needs a two-headed signal, they may have given   
   >> >> the right the same for consistency.   
   >> >   
   >> > A two-headed signal in which the second head is meaningless? That's a   
   >> > TERRIBLE idea and just flat out bad engineering. I certainly hope   
   >> > there are no real world examples of that.   
   >> >   
   >> > You don't see the adverse implications?   
   >>   
   >> I've seen several examples of two-headed signals where one track's lower   
   >> head has a fixed red; I assumed it was there for consistency (to match a   
   >> two-headed signal on the other track) since a lower red can't affect the   
   >> overall aspect, but perhaps there's another reason.   
   >>   
   >> I see _no_ adverse implications aside from a little wasted money.   
   >   
   >It is a 'dummy' head.  It is used to indicate that the signal is an   
   >*interlocking* signal as opposed to a *block* signal.  The rules for block   
   >signals are a little different from the rules for a interlocking signal.   
   >Things like absolute stop vs permissive stop.   
      
   Thank you!   
      
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