Railroad trackside signal lights

I might add that the Dispatchers model board display only shows if a signal has been lined - it does not show what indication the signal is displaying.

One bulb and three coloured lenses on a plate that swings back and forth. Red is in the centre so that if the control mechanism loses power it will go back to red from gravity alone, same idea as semaphores having the down (horizontal) position indicating stop.

This also means that as the signal changes from yellow to green or vice-versa you will see red for a brief moment.

We need a bit more detail here. The ‘incandescent bulb’ (and then LED) signals with three colored aspects, like for example the UP Darth Vader heads, indeed have three separate bulbs or diode arrays.

A typical semaphore spectacle has three colored lenses, with a bulb and reflector arrangement behind them. Ideally this hangs by gravity if motor power goes out, and the red light is arranged to be on with the blade as far down as it goes… what happens if the motor power also keeps the light lit is less often mentioned.

The signals like searchlight types have an interesting arrangement. These have very powerful condensing optics inside that focus the light very tightly through the area where the colored lenses are – these are very small, and much thicker than colored glass lenses in ordinary practice. Red, for example, can almost look black when you’re holding the thing. Operation of these is as Dude said, in a motorized frame, with red being the intermediate position during a change.

Of course, one consequence of PTC is that any signals that rely on a motorized or active system to choose aspects are deprecated or forbidden, which is why the searchlights are going en masse and I believe the B&O style CPLs are coming up for progressive replacement… may it take decades more! Same is true of any signal that can lose all aspects should a single bulb or element burn out… but less from a PTC than a PSR perspective.

I thought the search lights had to go away with PTC. That’s not been the case. We still have them at a few locations. When the signals get upgraded, they do get replaced with the three light types. I don’t believe there’s any time requirement for replacement.

The colored vane on the search light type can stick. I’ve seen it happen. That’s why they

Most, if not all, rule books have a rule stating that a Imperfectly Displayed Indication, when seen is to be acted upon as the MOST RESTRICTIVE Indication that that signal is capable of displaying. ie. STOP for an Absolute Signal and Restricted Proceed for a intermediate signal with a number plate.

I thought that was the case as well, but there may be some grace in non-passenger areas.

There are several still standing guard at Santa Fe Jct. in KCMO.

Last time I heard anything about the CPLs at Deshler, they were staying until they broke. Many of the signals at Deshler are Darth Vaders already, especially on the E-W line.

IMHO, CPLs could easily be changed over to LED - just a matter of replacing the bulb/reflector/lens assembly. There are no moving parts on the signal itself.

There are also several safety improvements for fall protection with the new masts. I assume a OSHA mandate.

A search for the following led me to the type of light you described. All of the replies help in learning the terms to perform more productive searches.

h2 searchlight mechanism

Thanks again.

tree68 and others,

Thanks for the insights. They are informative.

Upper quadrant semaphores were weighted on the blade. Lower quadrant semaphores were weighted on the lens holder. Either way, the failsafe was a horizontal blade.

This has probably already been addressed somewhere buried in this thread, but just in case, there are far more aspects than just CLEAR, APPROACH and STOP.

In the West, on the former SP, which I was the most familiar with, a flashing yellow signifies “advance approach” which means the NEXT home signal is in the approach position and the following signal after that at stop. This gives the engineer a little more time to react with a heavy, fast moving train.

A flashing red on an absolute signal indicates “Stop and Proceed”.

Red over green is “diverging route clear” which means the block ahead is clear but there is likely a permanent speed restriction on the turnout. The engineer has to be familiar with the territory to know what that speed limit is as provided in the “Special Instructions”.

Red over yellow is similar, “diverging route approach”. Once again, the switch is lined for a turnout but the signal indication is saying that the next home signal is at the stop position.

Yellow over green is “Approach diverging route clear”. This tells the enginer that at least the two blocks ahead are clear but, once again, there is a speed restriction on the turnout.

Yellow over yellow is similar. “Approach diverging approach”.

Then, I could get into SPTCo semaphore signals but I’m inclined to quite while I’m ahead. :slight_smile:

Some of the signals in the East, especially on ex-Conrail lines use what’s called “Speed signals”. Those a

You know, I wondered for much of my life as to WHY when semaphores had motors and electric lights why they didn’t just use colored light signals?

I had this explained to me by an old, nearing retirment age SP conductor on Amtrak’s Sunset Limited.

What he told me made sense. “Because they had trouble generating a light that was bright enough to be seen in the daytime.” DUH ~ ! This was especially true in much of the West where the sunlight can be very intense. Remember too that there was no electric power out in much of the American outback until after the Second World War. Solar panels were also far in the future.

These signals were powered entirely by lead-acid batteries and the signal maintainers had to go through once a month (or after some specified time period) and change out the batteries then take the spent batteries back to be recharged.

The counterweights and blades were held in the clear position by a rather ingenious locking mechanism that kept the mechanism locked by a minute trickle charge that used very few watts. When a train entered the block, that trickle charge was shorted out and interupted causing the locking mechanism

As I understand them…

They’re actually pretty simple. Per the example I gave earlier about the southbound signal on the SE wye at Deshler - The signal can never give more than a medium clear as the speed on the wye is 10 MPH, and the train will be going through a switch as well.

If you know the plant at a given location, you’ll begin to recognize that a given aspect also kind of indicates the route. On the SW wye, a clear (green with a top center marker) means the train will be proceeding straight down the west track to south Deshler, while a green with the upper left marker (approach medium) generally indicates that the train will be taking the crossovers to the Toledo main.

In each case, it’s the intended speed (as governed by the plant) that is being displayed, not the route.

Likewise, the signal governing movement from the SW wye to the E-W main (Darth Vaders) can never display a “high green” as the top head only has a red light. The middle head has only two choices, and one of them may be lunar, allowing a restricting aspect to be displayed. I don’t recall for sure.

Corrections and expansions welcome…

It’s always nice to see a good railroad signaling thread on sites like this.

Was your question answered? There are two main types of questions I get about US railroad signals:

  1. What does the signal I’m staring at mean?
  2. What? How does this system make any sense?

For #1… If you look at my site, you’ll see railroads like CSX and NS have multiple pages. Bankruptcies and mergers have brought many disperate signaling systems together over the years. It’s often considered too costly to install new, complying signals in the field, and too dangerous and inefficient to re-train crews on new signals for areas they’ve worked for years. So, for railroads like that, you have to know a bit of the history of the line for which the signal you’re staring at came from. Once you know the history of line you’re 'fanning, you will know which page to refer to.

Good news is, I do have three more charts in the works I hope to put up when I get them finished.

For #2… The system, generally, does make sense. But it’s not a system most people (even railroaders) are going to just work out for themselves. Al Krug did a great job explaning the general basics. Unfotunately his site disappeared, but an archive of it is available here. It’s a great read for anyone wanting to understand US railroad signaling. EAch railroad may have a slightly different signaling schema, but the basic concepts are pretty standard.

Railroad signaling is a complex and detailed topic, which is probably why I like it so much. I also find it fascinating how little 8-inch lights can tell a 20 million pound train what to do.

Many years ago, on my first trip aboard the Canadian, a retired CN dispatcher sat next to me in a dome car and he explained the oncoming signals as we proceeded West. At one point he said he thought the dispatcher was just giving the engineer a hard time with the signalling setup.

The following site is basically what you posted but with different formatting.

http://www.mikeroque.com/understanding-railroad-signals/

As with most of railroading, some of my questions were answered here, others by searching. There are too many variations to have them all answered (or for me to know what all to ask).

This goes for all of the rest of railroading. It’s been evolving for a very long time so unless a very specific question is asked, the answer will likely be incomplete. Getting questions answered (for me) has been best if I have done enough researc

That is perhaps the beauty of B&O’s old color position lights (CPL’s). While there was a specified full complement of lights included by the system, in reality specific installations only had the light heads that were needed.

You can read all about them here: https://railroadsignals.us/signals/cpl/index.htm

Most railroads’ signals are somewhere on the web. You’ll find that while there may be some different configurations, and the rule numbers are specific to each railroad, but in the end the meanings are very similar.

If you follow a specific railroad, concentrate on learning their system.

One thing I don’t have down yet is the modifier that is a flashing head.

All that said - if you remember that red is stop, amber is approach, and green is go, as well as (in general) top head is track speed, middle head is medium speed, and the bottom head is slow speed, you’re probably 90% there.

It may be a bit dated, but I have found that my copy of “All About Signals” is still useful in providing the basics. With an assist from a couple of “Rules for Conducting Transportation” in my collection, I can read most signals reasonably correctly.

What can get interesting is figuring out the situation with reverse signalled track governed by CTC.

Action on CSX Old Main Line

https://www.youtube.com/watch?v=8uKqhSTOg_4