From: stephen@sprunk.org   
      
   On 03-Mar-16 17:36, Robert Heller wrote:   
   > At Thu, 3 Mar 2016 12:00:56 -0800 (PST) hancock4@bbs.cpcn.com wrote:   
   >> For a green over red, (Rule 281 Clear--Proceed), does it make any   
   >> difference if the signal is a home signal at an interlocking, or a   
   >> block signal with a number plate?   
   >   
   > I believe most of the time these days, the upper head of a   
   > multi-head interlocking signal is the same as a block signal for the   
   > straight route.   
      
   If you simplify that to just multi- and single-head, then it is true in   
   most cases: you can ignore any trailing red (or dark, which is read as   
   red) heads.  NORAC has one exception: red/yellow/red is _not_ the same   
   as red/yellow.  I'm not aware of any exceptions in GCOR, but it's hard   
   to be sure since they don't have standardized signals.   
      
   Other systems, however, may have entirely different aspects for home,   
   distant and/or block signals, e.g. IRT.  Or they may have an entirely   
   different way of organizing/using signals in the first place.   
      
   > The only 'gotcha' is that red over red [over red] (all heads showing   
   > red) always means stop right here (absolute stop) -- often because   
   > the points might not be aligned or there is some other conflict (like   
   > a crossing). A single head red (simple block signal) is stop and   
   > proceed at reduced speed, expecting to stop when catching up with a   
   > train ahead.   
      
   Multi-/single-head is orthogonal to home/distant/block.   
      
   There may be multi-head distant/block signals, where red/red or even   
   red/red/red means Stop and Proceed, and single-head home signals, where   
   red means Stop and Stay.  That is why the number plate is needed to   
   distinguish between the two!   
      
   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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