From: stephen@sprunk.org   
      
   On 02-Jan-16 16:36, Adam H. Kerman wrote:   
   > Stephen Sprunk  wrote:   
   >> On 02-Jan-16 14:48, Adam H. Kerman wrote:   
   >>> Stephen Sprunk  wrote:   
   >>>> 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.   
   >   
   > Nobody erects a signal head to be decorative.   
      
   Consistency could be considered functional rather than decorative.   
      
   > Note: There is a location on the CTA "L" in the Dearborn subway with   
   > such a signal head. It's where the turnout into the downtown   
   > terminal for the O'Hare Express service would have been built. No   
   > special work for the turnout was ever performed, but for no valid   
   > reason, they erected the signal mast and head before any other work   
   > was done. The project has been cancelled for years but the signal   
   > wasn't removed.   
      
   It costs money to remove things.  If it doesn't have any adverse   
   effects, why bother?   
      
   > If CTA does it, it's stupid.   
      
   *eyeroll*   
      
   >> I see _no_ adverse implications aside from a little wasted money.   
   >   
   > What if the signal head the engineer or motorman is required to obey   
   > burns out? Seeing the other signal head will be confusing.   
      
   Dark over red is invalid but looks like a stop signal from a distance,   
   which is fail-safe and probably better than a completely dark mast that   
   the motorman may not see--and which is also treated as a stop signal if   
   he _does_ see it.   
      
   > What if the signal head he doesn't pay attention to burns out? Then   
   > he's supposed to follow the fail-safe rule.   
      
   If there's no diverging route, then the second head being dark is   
   irrelevant; it can be treated as a single-headed signal.   
      
   Note: this is only true for IRT-style signals; it is _not_ true for   
   BMT/IND-style signals, where the second head cannot be fixed red.   
      
   > You're just going to be stubborn and not acknowledge the obvious, I   
   > know.   
      
   What you consider "obvious" may not be so.   
      
   >>> 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.   
   >   
   > Why not leave the old signals active?   
      
   If you're going to leave them active, why put in new signals?   
      
   > It's decorative, according to you.   
      
   I never used the word "decorative"; that was your description.   
      
   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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