On Friday, March 11, 2016 at 12:09:29 PM UTC-5, Joseph D. Korman wrote:   
      
   > A clarification of the Transit Call-On (at least in NYC):   
   > Not only does the tower have to activate the white light (R/R/W), the   
   > train operator must push a button or lever on the signal head to lower   
   > the stop arm.  If the tower hadn't activated it, the button/lever will   
   > not work for the T/O.   
      
   In the old Phila subway-el signal system, only the tower operator's   
   action was required.  I believe the board was interlocked so the   
   towerman could only issue a call-on under certain conditions; such   
   as the interlocking itself being free of train, but perhaps a train   
   on the adjacent station platform.  In this way, a train could be given   
   clearance to approach a platform slowly as its leader is leaving.  IIRC,   
   it wasn't frequently used.  Anyway, I think the conventional signals on   
   both BSS and MFSE have been replaced.   
      
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