Like I said, at first glance the C&O looks like a very responsible Northeastern style railroad. You have your Y/G Approach medium, even Y/Y Approach Slow! That's a big step up on the New York Central and others with Y/Y for Advance Approach.
|Exit signals invite Approach Slow|
Oh boy, yeah, not I see the problem. R/Y/Y is Medium Approach. It looks like the entire indication was an afterthought, sort of like how the PRR used to diverge trains to stop over Approach until 1956. Still, if you have a third head to play with there is no need to see the cost of flasher relays come down. Makes me wonder if they could have gotten away with R/R/Y for Slow Approach and R/Y/ / for Restricting. This is one of the few cases where a red lamp is lit to upgrade a dark head and upgrade the signal indication (in this case from Restricting to Slow Approach). This is also one of the few cases where Restricting is more common operationally than Medium Approach.
|Doing with 8 lamps what other railroads do with 9.|
|Enter interlocking? Pass a signal. Exist interlocking? Pass another signal.|
This brings up another quirk. The C&O placed its Red lamp in the upper position on its upper head and the bottom position on the second or middle head. This gave a wider spacing between Red lamps, but made the concept of "high" green a bit less applicable.
|Low high green?|
Bottom placement of the R lens on dwarfs allowed for Y/R Slow Approach with Y being Restricting, avoiding the need to flash Y as seen on NORAC. R/Y was also a Restricting Option.
Slow Clear could be either G or G/R, but in a bit if clever thinking the C&O went with *G* to upgrade slow speed siding exits to Medium Speed, as opposed to NORAC going with G/*R* and leaving *G* for the less applicable Limited Clear. The rest of the C&O scheme was all pretty standard with the usual mix of Approach Medium/Limited and Medium/Limited Clear.
|Is there a slow speed route? No, just Medium Approach.|
It's a real shame there isn't much room in our national rail system for unique and interesting signal systems such as this. Not only does the C&O suffer from not being as lamp efficient as some others, it is a bit less intuitive, relies on dark signal heads and conflicts with many other more popular systems. Going forward only the Buckingham Branch shortline appears committed to the C&O system, however as they remove the remaining signaled sidings on the C&O Washington route there won't be much of an occasion to show it off.
BTW, I am celebrating a milestone at The Position Light today with my 251st post.