From: ahk@chinet.com   
      
   Stephen Sprunk  wrote:   
   >On 02-Jan-16 01:46, spsfman wrote:   
   >>>Stephen Sprunk  wrote:   
   >>>>On 01-Jan-16 02:32, spsfman wrote:   
      
   >>>>>I saw a flashing green over red on the not open for business   
   >>>>>yet Phase II Expo Line here in Los Angeles. This is light rail,   
   >>>>>and they began running test trains in November. I saw the   
   >>>>>signal last week.   
      
   >>>>>It was on the right hand track, which would be the usual   
   >>>>>direction of travel. The left track had red over red. This is   
   >>>>>the first signal after leaving a station, if that means   
   >>>>>anything.   
      
   >>>>Assuming this was at an interlocking, green (flashing or not)   
   >>>>over red sounds like an IRT-style signal, where the upper head is   
   >>>>the speed for the main route and the lower head is the speed for   
   >>>>the diverging route; at least one of them is always red.  I've   
   >>>>never seen flashing green on such a system, though, only flashing   
   >>>>yellow.   
   >>>>...   
      
   >>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?   
      
   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.   
      
   I don't buy it.   
      
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