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Eastbound is clear | by Jer*ry
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Eastbound is clear

No, wait -- I think that's a bird on the track!

I used to wonder about RR signals like this -- what the heck does it mean when both the green and red are showing?? So, I posted a question on a UseNet group and as one might expect, got lots of replies. Among them 1 or 2 fairly lucid answers, such as this:

 

It means "Clear Signal", Proceed at authorized speed.

The aspect displayed, green over red, is simply one aspect that is used

for a Clear Signal. It means the same thing as a single green aspect, or

a green over red over red, where three signal heads are provided on the

same mast.

In this case, the bottom head is called a marker, since it cannot display

anything but red. The reason the bottom head is provided is for light-

out protection: If the bulb in the top head should burn out, the crew on

an approaching train will still see the red, which would indicated a stop

is required. Otherwise, the red really has no effect on "Proceed"

indication.

If the bulb in the marker burn out, then the crew would see the single

green, and there would be no safety implication. (They would still have

to stop to report an improperly displayed signal, when they saw the non-

working head, but it really doesn't matter if they ran past it before

stopping.)

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Uploaded on January 19, 2007