From: stephen@sprunk.org   
      
   On 15-Jan-16 13:55, Joseph D. Korman wrote:   
   > On 1/9/2016 6:02 PM, Stephen Sprunk wrote:   
   >> On 08-Jan-16 11:46, Joseph D. Korman wrote:   
   >>>>> Stephen Sprunk  wrote:   
   >>>>>> 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.   
   >>>   
   >>> On the NY subway BMT-IND and new IRT signals, there would be a   
   >>> bottom head that only displays green or red.  This is an   
   >>> interlocking signal protecting a training point switch, so the   
   >>> only valid aspects are G-G, Y-G or R-R.   
   >>   
   >> In the case above, there is apparently _no_ switch on this track,   
   >> trailing point or otherwise.   
   >   
   > I'm not sure why you think there no trailing point switch.   
      
   According to the FEIR's track diagram, there are no switches (trailing   
   point or otherwise) on the right track near the location that the OP   
   asked about, only on the left track.  I see a few possibilities:   
      
   1. They added a switch on the right, e.g. a crossover to reach the yard   
   lead switch on the left, that wasn't on the diagram.   
   2. The right is part of the interlocking despite having no switch.   
   3. They used a two-headed block signal on the right for visual   
   consistency with the left's home signal.   
   4. They don't actually use IRT-style signals, and there's some aspect   
   that requires two heads on a non-home signal.   
      
   That's my guess as to the order of probability, but until the line opens   
   or satellite photos are updated, we can't confirm or refute #1.   
      
   I see no way to confirm, refute or even distinguish between #2 and #3   
   without insider knowledge.   
      
   Someone riding other parts of the system might be able to confirm or   
   refute #4, but I can't find much about transit signals _anywhere_ other   
   than NYC, just my observation that every system I've ridden appears to   
   use signals that conform to BMT/IND or IRT style, which (in contrast)   
   are well documented.  But I'm not holding my breath.   
      
   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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