Search This Blog

Saturday, December 3, 2016

Well, There's a New One

Last week, while on a field trip to Chicago, I encountered a new Class 1 railroad signal indication I was hitherto unaware of.  Approaching Tower B-12 interlocking on the former Soo/Wisconsin Central line (now owned by Canadian National) to Chicago on a METRA North Central Service train, I saw a signal flashing yellow over a steady green (*Y*/G)  This was nothing I had ever encountered before, however it was not difficult to surmise that it was Advance Approach Diverging.  At the next interlocking I was proven correct as a Y/G Approach Diverging was displayed for a R/G Diverging Clear at Tower B-12.  The Advance Approach Diverging was warranted for the short signal distance between the Approach Diverging at Junction 16 and Tower B-12.

Upon reviewing my CN documentation from 2010, both this and Diverging Clear Approach Diverging (R?*G*) were listed in the operating rulebook, so I should have been aware of it, but I usually refer to the late 90's rule card I have in a more accessible location.  I suspect that the signal was likely deployed for the first time for the re-signaling project on the NCS line and might even be a unique situation.  It's still an interesting developing for a route signaled line as most others begin to employ speed signaling to various degrees.  Of course I should save any more in depth analysis for my BKASS article on CN route signaling ;-)


  1. NYC also had advance approach medium G/Y. Used between Woodlawn and GCT to achieve 4-block signaling. For this reason used G/G for clear. Lasted until MetroNorth resignaled in 90's.

  2. Advance Approach Diverging is common on the CN Waukesha Sub and is used two signals out from almost every diverging route between Tower B-12 and Grayslake and at some other locations north of there. The aspect was added during the expansion/double-tracking project in commuter territory in 2002-2005. I believe FY/G is always used in Illinois currently, but a single FG (flashing green) can be seen in Wisconsin (and the latest rule book has FG/R too). The Waukesha Sub has had a very interesting signal and signal aspect evolution – I can send more details if you’re interested. Dave Malohn

    1. Yeah, that would be great! It's interesting how many short signal blocks appear when public funding is involved.

  3. The short blocks do a good job keeping the line fluid though, so it’s helpful they have them. The bigger problem these days is for the lineside commuters when the dispatcher uses the short second main at Grayslake to make meets with freight trains during rush hour…

    Is there a place on here where I can upload/send you a file with other details on the signaling on this line, or must I paste everything in a comment?