Western Railroad Discussion > Those Blinking Signals

We hear numerous train engineers report a blinking yellow signal. How is a blinking yellow different from a steady yellow? Don't go on to say there are also blinking red and green signals.

Well, basically, a blinking yellow is in between a green and a hard or steady yellow. I don't know what rr you are refering to, but on the UP a flashing yellow is Advance Approach, on the BNSF it is called Approach Medium. I have heard it explained that as train speeds increased, a intermediate indication was needed to get trains that were going, say 70, slowed down enough to stop at a red. If a train was approaching a red 4 blocks a way, it would get a green, then a flashing yellow, then a yellow, then a red. Many variations exist and there are yellow over greens that are sort of in between a green and flashing yellow.

Yes, there are flashing reds and greens.Flashing reds usually means restricting, and I have heard UP uses a yellow over flashing green to authorize 60 thru their movable point frogs. There are many different varities of signals and indications. I will see if I can dig up some links for you and post them here.

Steve

There are a bunch of signal aspects that use flashing yellow, red or green. First to answer your question: Flashing Yellow (I've never heard "blinking" instead of "flashing" used on the railroad) is called Approach Medium or Advance Approach, and basically is an advance warning in high speed territory that the next signal will be Yellow, or will require you to pass it at medium speed. The exact application does vary with the railroad the signal is on, but it means "Slow down, the next signal isn't green, but in't red either."

If you want to see all the signal aspects used on the BNSF, go to http://www.bnsf-ttc.com/bnsftime/index.html , click on "I accept" then download the "Signal Aspects and Indications. Anothe good option is to get an Altamont Press Railfan Timetable, which has all the aspects and indications in it.

On the Missouri Pacific flashing yellow was Approach Medium- reduce speed to 35 mph before reaching next signal. Advance Approach was a double Yellow- reduce speed to 50 mph before reaching the next signal. I worked for the UP from 1982 to 1990, and I sure don't remember them swapping those 2 signals around as one poster said.

The general concept behind flashing signal lights is to provide an economical way to display a slightly more favorable indication than if the flashing light was on continuously.

The safety engineering behind this runs a bit like this. Since flasher circuits are a little less reliable than constant-on circuits, the failure modes must always be less favorable, not more favorable.

For example, here in the East under NORAC rules, a red-over-green-over-red is generally Medium-Clear. That is, two clear blocks ahead over a medium speed route. If the green aspect is made to flash, then the indication is Limited-Clear which is two clear blocks ahead over a limited speed (faster) route. Now, if the flasher circuit should fail so the green is on continuous, the speed drops from Limited to Medium. If the flasher circuit should fail so the green is not lit at all (dark), then that light must be interpreted as its most unfavorable aspect possible which would usually be red. Red-over-red-over-red is Stop. Clearly both failure modes do not compromise safety. If the flashing lite were to mean a less favorable indication, the failure mode of the light being on continuously would compromise safety since it would indicate a more favorable speed or route.

Hope this is useful or interesting to someone out there!

On the BN during the late 70's, early 80's, they provided the capability for a flashing yellow for the approach signals on either end of the Crest siding which is between Denver and Brush, CO. Since Crest was in a "bowl" and you couldn't see the signals until you were practically on top of them, the flashers were installed. A flashing yellow indicated that you were going to hold the main line with the signal at the far being red and a steady yellow indicated that the next signal was red or you were heading into the siding.

To add some east coast insite:

NS uses flashing yellows.

CSX has flashing greens and some flashing yellows.

NS uses flashing yellow like the western roads.

On CSX high speed turnouts get a red over flashing green, or limited clear, which as stated above is faster speed than red over green, diverging clear. A lot of new locations are getting the flashing greens in eastern W Va.

CSX also has a flashing white on the B&O position lights for restricting if my memory is correct. I haven't seen this signal often but do remember it at Sand Patch.

On modern CSX signals lunar (off white) is being added to many heads in the form of a fourth light in the three head stop light style.

On the BNSF, a flashing yellow is Approach Medium which in laymans terms means to pass the next signal prepared to enter a diverging route ie take siding or crossover and not exceed 40 mph. Flashing red of any kind is a restricting signal, go at restricted speed. Then we also have a Yellow/Flashing Green aspect (on a double target signal) which is called approach limited, which is a 60 mph signal

Santa Fe

If there's one thing I've learned over the years, its that there are no nationwide rules about signals. Basically, the aspects mean whatever the railroad says they mean. And, in most cases, they all say something different!

About the only universal rule I would hazard to put forward is that red-over red and red-over-red-over-red is Stop and Stay Stopped. And I'm sure there are exceptions to that somewhere! (I know! Grade signals, etc. etc. etc). I may regret I ever posted this!!

The above messages just about covered it.

Around here we call them Approach Medium, Blinker, Winker, Flashing Yellow, Flashing, Flasher, and Pervert. That last one is fairly common and usually gets a grimace from the Trainmaster or RFE if I call it when they are riding with me. Just about anything to break the monotony.

And yes, Red over Red is not always a Stop and stay stopped. On our part of the BNSF we have several that have number plates so are Stop & Proceed. A few years back when BN had Restricted Proceed instead of Stop & Proceed you could go by them without stopping like you can on the MRL today. When I worked on the NYC just about all signals had at least two lihgts. So Red over Red intermediates (Stop & Proceed) were the norm.

The Santa Fe at one time used flashing green to indicate "approach-limited" "Proceed, approach next signal not exceeding limited speed, and be prepared to enter diverging route at prescribed speed" (rule281A, 1959 rulebook). This indication was used in advance of higher speed switches and was used at Fullerton Calif. MediumClear noted that for safety flashing aspects were less restrictive than the solid color, however this is the opposite. The problem would exist if the straight through speed was significantly higher than the diverging speed. Eventually, these signals were modified to two heads and the flahing green indication was replaced with yellow over green or yellow over flahing green.