From: heller@deepsoft.com   
      
   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.   
      
   >   
   > > On railroads, whenever I've seen signal work, whenever old signals   
   > > are replaced with new signals, they indicate that the old signals or   
   > > new signals are out of service by turning the signal heads. I have   
   > > never seen an instance of an active signal representing nothing on a   
   > > railroad.   
   >   
   > Turned heads and unused/fixed second heads are completely different; the   
   > former are out of service and the latter are in service.   
   >   
   > S   
   >   
      
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