|2 x Clear at HOLMES|
|CP-437 in South Bend, IN|
NORAC color light signals are typically built around two head masts, but every so often the third head makes an appearance. This is either when there are slow speed routes or back to back interlockings requiring R/Y/G Medium Approach Medium.
|Medium Clear at CARROLL|
Of course the more spectacular complete signal is the B&O CPL with a full central target and all six orbitals. These were especially rare due to the need to have a back to back interlocking with slow speed signals at the next interlocking down to allow for both Approach Slow and Medium Approach Slow. Due to a similar preference for Stop and Proceed over Restricting, one also tended to need routes into un-signaled track. As a result this signal went extinct in the wild twice. The first being after LAUGHLIN JCT and CURTIS were downgraded and/or resignaled and then again when CARROLL interlocking was first upgraded in 2007, only to be resignaled in 2012.
Sticking with the Chessie system, the C&O's example of a full signal was quite a bit more common than the B&O's. The use of R/Y/Y for Medium Approach made lower heads rather common. Add in R/Y/G for Medium Approach Slow (or Medium) and you'll get a complete 3-3-2 configuration as seen above.
|CSX SATERWHITE interlocking at the Point of Rocks wye complex.|
|3 by 3 in Salisbury, NC.|
|The late great HULL interlocking.|
The N&W PL system has it even easier than it's PRR cousin to force a full signal. Without the central market option for a Stop and Proceed, any need to enter an occupied or unsignaled track triggers the need for a lower head \. Standard use of Diverging Approach covers the / position as well.
|Four headed monsters at KENSINGTON.|
|Southern Pacific's HOWARD Interlocking|
However there is one signal that we've left out. This is the Y/L "Approach Restricting" typically used to signal an upcoming route into a siding on a single track main line. With no Y/*R* option, Approach Restricting requires a lunar lamp and combined with the need for a second slower speed route one would see a 3-4-3 or 3-3-4 signal, just like on METRA or CSX. These however are incredibly rare. So rare that I do not have a photo of one in my collection (although I am sure one exists somewhere). As UP has a new policy of using Approach Restricting at places with common routes into unsignaled track, UP is the more likely road to have a full signal of this type. The best I could find was this 9-lampbeast in a 3-4-2 configuration at SWANSTON interlocking near Roseville, CA.
If you have or know of a photo of a UP 10 lamper let me know and I'll update the page :-)