Signals - Green on top of Red

When the early railroads used a Ball on a pulley as a signal, the upper position of the ball indicated "Proceed". Hence the term "highball". Placing the green light at the top emulates that.

 

There are some railroads that do use signals with red on top, similar to traffic signals. Some train order signals were horizontal, with green usually on the right.

kind of a guess,i always thought a red aspect was on the bottom for best visibility to the engine crew,it being the most important to see.-jim

Red over green and green over red mean entirely 2 different things. The bottom aspect indicates the diverging route. Green over red means you're going straight. Red over green means you're taking the diverging route.

Alex, I was reading something about this recently.  I have been trying to locate what it was that I was reading, and have not been able to, and my memory is sketchy.  Basically, it had to do with the pre-electricity history of signaling, as GN Man points out, and it has to do with a fail-safe default.

 

Before lights, there were semaphore arms, and the first semaphores were configured so that the horizontal arm meant stop, and then the arm dropped down for go. ("Lower quadrant" semaphores.)  The problem with this set-up was that if the semaphore malfunctioned (broken control rod or cable), the default due to gravity would be that the arm fell, giving the go-ahead signal.  Obviously, this was not good.

 

So by 1900 semaphores were changed to be horizontal for stop, then the arm was pulled up for the go signal ("Upper quadrant" semaphores.)  The default position should something malfunction and the arm dropped, would now be "stop".

 

When electricity was added to these semaphores, the green lens ended up being on top, like this:

 

 

 

 

and as emulated by this Ives semaphore from 1923:

 

 

 

 

So then, when signals went to being just lights, the same arrangement with green on top was continued.

 

I think that's the gist of what I read, I'll keep trying to find it.

 

Of course, we've all also seen semaphores that use upper quadrant signaling but have the red lens on top, depending on how the semaphore is constructed and how the arm pivots. So I'm not sure how water-tight this theory is.  But I do think it has to do with pre-elecricity signaling, and the convention then carrying over into the electric light signal era.

 

 

 

As Hojack noted above Should a signal fail it would "fail safe" to the red position. a semaphore would drop down into the red position. This could also be caused by snow fall birds on the semaphore etc. etc..  A dark signal is also to be considered a Red aspect. Failure of the linkage would drop it to the red position.  The electric color position signals mimicked the semaphores to keep the signal advancement as simple as possible with the crews. Green would be up down, red was left to right. Your asking about the D type signal.

 

There is a very detailed explanation of this in the book "Signals"   

BTW electric signals for trains pre-date 'stop and go' electric signals for automobiles. 100 years ago, some busy big-city corners had traffic cops directing traffic using manual stop-and-go semaphore signals located in a small island in the middle of the intersection. By moving a lever, the semaphores say for the north-south route would go to 'clear' while the east-west ones would go to 'stop'.

I really appreciate your very informative answers - Thank You!

 

The reason I was asking is that I will 'soon' be offering a new product that will include a red & green annunciator of the position of turnout points, or train route - Green will mean straight-through, and Red will be diverging.

 

Part of the product will be a two-LED (green and red) annunciator as well as a single, bi-color (green & red) LED, either of which can be installed in close proximity to the layout and/or the control panel. No issue installing the single, bi-color LED, but I wondered about the individual green and red LED's, and where the colors should be placed. 

 

My patent-pending* non-contact detection method reflects the true and actual position of the throw bar, and hence the points, and is totally independent of the switch machine. As we know, the switch machine could well be in one position, and the throw bar in the other or in between, which happens at the most inopportune times. My method never gives false indications. Furthermore, if the throw bar and points are not fully in one or the other position, neither the green or red light will illuminate, which will indicate partially thrown points.

 

*I had filed a provisional patent application in March 2013, and yesterday I filed the final, non-provisional application.

 

More to come soon -

 

Alex

Another reason for red being at the bottom, is that it is less likely to be obscured by snow than the top aspect. Another part of the 'fail safe' philosophy in signaling.

 

But,,,,,what if the snow is REALLY DEEP?

 I was meaning snow landing on the signal from above. But, if the snow is deep enough to obscure the signal from below, then I'd suspect that the train crew might have some other more pressing problems. 

FWIW originally three color signals were clear or "lunar" meaning the track was clear, green was "caution", and red was "stop". Problem there being if the red lens fell out, it would give a lunar (clear) indication. So early in the 20th century the still used green-yellow-red combination began to be used.

 

Some railroads still use lunar as a fourth indication, for example, to show a switch ahead is a spring switch.