"1 over 1" signal - how to these and others on a layout?

signals with the ablity to display two different colors, like Green on the high signal and Red on the lower signal are just a better way to control trains.  A Green over Red would be a Clear signal.  A Yellow over Yellow is advance approach on the Norfolk Southern.  That is telling the crew to be prepared to stop at the second signal.  Yellow over Red is a regular approach indication.  So they would be prepared to stop at the next signal(red over red stop indication)   There are many other variations depending on the railroad itself, some add flashing to one of the 2 aspects displayed.   You can google search railroad signal indications or pick up a timetable/rule book off ebay for your favorite railroad.   It would have pictures showing all the different signal indications that the crew might see while running on that line.      Mike the Aspie

PRR signals could be used for what you proposed for a PRR, PC, CR, and any NS or CSX lines which got ex PRR lines ar the CR split provided they have not been replaced.

As you have seen, above, it all depends upon which railroad and which period you're modeling.  PRR Position Light (PL) and B&O Color Position Light (CPL) signal heads are disappearing rapidly leaving us with "color light" only signal heads, regardless of configuration.  I had to look up Railking "1 over 1 signals" to confirm that my guess at the type and configuration were correct and here they are:

The above are "searchlight" type signal heads.  Your "1 over 1" signals are intended to govern where diverging movements (switching from one track to another) are a possibility.  They can serve as a simple block signal, warning of the condition of the block or signal aspect ahead; warn of a diverging movement at the next signal; or warn of the condition of the block on the diverging route when located at the entrance to an interlocking (trackage which includes a switch or switches, entry to which is governed by signal indication).  Follow this link (below) to a page showing the UP's signal aspects and their indications:

http://signals.jovet.net/rules...20Signal%20Rules.pdf

A quick Google search will bring up an equivalent page for whatever other railroad(s) you may be modelling.  Railroad signalling is a fascinating subject and the most reliable systems still rely on the simple shunting of track circuits, technology invented by Dr. William Robinson in the 1870's:

https://en.wikipedia.org/wiki/William_Robinson_(inventor)

The Atlas O 21st Century Signal System for 3R uses the same simple technology as the real thing:

http://download.atlasrr.com/Tr...Signal%20Systems.pdf

Eric Siegel has an excellent two part tutorial regarding the system which explains it all beautifully:

https://www.youtube.com/watch?v=Y31p1AiPaWA

https://www.youtube.com/watch?v=6bUWymTNBHo

Enjoy full immersion railway signalling, you'll never be bored again!

Thanks much - very helpful links and videos.