From: stephen@sprunk.org   
      
   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.   
      
   > 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   
      
   --   
   Stephen Sprunk         "God does not play dice."  --Albert Einstein   
   CCIE #3723         "God is an inveterate gambler, and He throws the   
   K5SSS        dice at every possible opportunity." --Stephen Hawking   
      
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