How to read railroad signals
Curious about it mostly, have looked up charts a couple of times now and found a lot more signal combinations than I expected to see.
But on a typical US railroad, how would the signals be read by the train crews? What combinations are typically shown and what do they mean?
This is an entire subset of railroading that many railfans know very little about, since it doesn't come up in conversation unless someone asks.
Re: How to read railroad signals
It has been a long time now, but I remember the basics, though they vary by road and with time. I worked for the BNSF over 15 years ago. This will be rusty at best. There are also different types of signaling systems in place. From as simple as a block signal system to CTC.
Green is pretty basic. It means Proceed. Your maximum allowable speed would be train speed / track speed. These each vary considerably for a variety of reasons.
Opposite end of the spectrum is Red. It *almost* always means Stop. Unless it is a Grade Signal, in which case you may proceed at Restricted Speed, without stopping. I believe these will have a G sign under them, but regardless they would be noted in the Timetable.
Restricted Speed means a speed which allows you to safely stop your train within the distance you can see, and not to exceed 20 mph. This can be extremely slow under certain circumstances. Like a couple mph.
If the Red indication is at an Absolute Signal, as found at a control point for instance, you must remain stopped until the signal improves. Unless the dispatcher gives you authority past the signal.
If it is an Intermediate Signal, after stopping, you may proceed past the red signal at restricted speed. You don't have to proceed though. It's easier from a train handling point of view to wait for it to improve instead. Ie train ahead leaves that block, and you would get a Yellow.
Flashing Red means the same as Grade Signal. Proceed at Restricted Speed.
Yellow (IIRC, this is called an Approach indication) used to mean "Trains exceeding 40 mph immediately reduce speed to 40 mph and proceed prepared to stop at the next signal". Too many crews were getting through Red signals though, so they changed that 40 mph to 30 mph some time after I left.
A Flashing Yellow (Advanced Approach) means the next signal may be Yellow. I don't recall if any action is required. It may be that you cannot pass the next signal in excess of 30 mph if it is indeed Yellow. These are common but not universally present. Frequently you would just have a Green preceding a Yellow. Probably partly depends upon block length and track speed. Blocks are usually ~1-1/2 - 2 miles.
A Flashing Green. I don't ever recall seeing one of these. I remember being told that Amtrak uses them. And I think I recall that they are called an Approach Limited. I don't recall the rule though. Maybe something like reduce to 60 mph. Don't recall.
There's also a Lunar Signal, described as a "dirty white" color. I want to say these were used in conjunction with yards, but don't quote me on that. I don't remember, and I don't think I ever saw one.
---------- Post added at 10:36:33 PM ---------- Previous post was at 10:14:49 PM ----------
So then you've probably seen where there are two signals, one above the other. These precede a switch, both immediately before it and one block ahead of that.
To simplify, the upper signal tells you about the track you're on, and the lower signal tells you about the adjacent track(s), or more precisely whether or not you will be taking the diverging route, ie switching tracks.
These double signals will both immediately precede a crossover or turnout, and be present one block in advance of the crossover or turnout.
So if you are looking at the advance signal, and you see a Yellow over Green, it means Proceed (the Green) AND that you will be taking the diverging route at the next signal (the Yellow). Note that turnouts have their own speed limits (50 mph is typical, but by no means universal) and you must be prepared to pass the next signal at or below that speed. This is the primary reason for the advanced signal.
In the case above, the next signal would be Red on top and some other Proceed indication below (ie Green or Flashing Yellow, or Yellow. The Red on top means you are now taking the diverging route.
If the advance signal is Green (or Flashing Yellow or Yellow) over Red, it means Proceed, AND you're staying on that track.
You can start to see that it's logical, and can figure out other scenarios. Lets say the Advance signal is Yellow over Yellow. That means you're taking the diverging route AND the next signal may be Red, ie proceed prepared to stop blah blah blah. The next signal would likely be Red over Red. And when it improves it will be Red over some other Proceed indication.
This can go on and on lol.
Last edited by Vanman; 08-02-2019 at 02:13:53 AM.
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