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CHAP 1 - Introduction
CHAP 2 - Signals Common in the United States Today
CHAP 3 - Glossary of Signal Terminology
CHAP 4 - Reading And Interpreting Railroad Signals 1
CHAP 5 - Reading And Interpreting Railroad Signals 2

So what are signals?  We know what they are when we see one sitting alongside the tracks (commonly referred to as a wayside signal), but how many of us think of a flag as a signal?  There are also hand signals whistles and horns, and crossing signals, in addition to the familiar wayside signal.  We also consider signs as a type of signal.  Each has its own specific purpose and method of communicating information.  Signals came about because there was a need - because there was no other way to get the desired information to the engineer.  This website concentrates mostly on wayside signals you can find in the United States today.

If you go cruising around the internet, you will find a lot of information on railroad signaling.  Some sites are better at explaining the principles than others.  The website for the Railway Technical Web Pages (1) is one of the better sites around for explaining things in an easy to understand format, along with some really good graphics to accompany the discussion. You will hopefully consider this site as one of the better ones.

Volumes can be written on early signals.  As such, there is a separate section that deals with them on this website.  Another good reference is (2) – JB Calvert goes into detail with numerous illustrations, and includes many references to many American signs and signals.         

Outside of the basic three aspect color light signal, most railroad signals are confusing to the uninitiated, and it makes no matter which type of signal you are looking at, what railroad you are on, or what country you are in.  Fortunately for the world, every country in the world has decided to use the same three colors in their traffic lights, and those colors dominate the railroad industry as well.

The simple three color light signal  can be roughly interpreted the same as a standard auto traffic light:  Green -- go, yellow -- slow down, and red -- stop.  It’s the definition of railroad signals that sets them apart from the above interpretation.  Most railroads would name those aspects clear, approach, and stop.

In the United States, most signal systems relay either speed information (predominate in the east) or routes (prevails in the west) to the engineer.  In Britain, signals indicate the condition of the track ahead, and it is left up to the engineer to adjust his speed accordingly.  This generalization does not preclude the signals from also displaying the status of the blocks ahead with the American systems, as we will see later.

The signal systems of today are becoming increasingly all electronic, replacing a cabinet full of vital and non-vital relays with redundant computers.  Even though computers still need some sort of output device (like a relay) to isolate and handle the bulb current, we are finding these jobs handled more and more by solid state relays.  The reasoning behind this effort to update and replace is simple -- cost.

Rulebooks, most of which contain signal aspects for the territory they cover, are interesting reading.  In addition to wayside signals, they also provide the reader with hand signals, whistle signals, and the rules that govern the operation of the railroad.  In looking over various rulebooks, many of the east coast railroads adopted a similar structure to their rulebooks.  For most, the signal rules were numbered 281 (clear) through 292 (stop) for defining the regular wayside signal indications.  For some reason, western railroads seem to organize their rulebooks with the signal aspects covered under one numerical section, and the different aspects used different letters.  For instance: the UP has all of their wayside signal aspects in rule 245, using rule 245A for clear, to rule 245Q for stop….. their cab signals are in rules 246 thru 246C.

Here's a link to the rulebooks in my rulebook section.

If you are looking for a good all around explanation of model railroad signaling, I recently came across this PDF by Richard Johannes:

Scientific American had a great article on the electro-pneumatic block signal in the April 5th, 1890 issue if you can locate it.

Sidebar - In talking about inventing things, the U.S. Patent Office is responsible in the United States for issuing patents on inventions.  They had their start in 1790, but formally became the Patent Office as we know it today in July of 1836.  They also had “the great fire of 1836” (3), in December, which destroyed about 10,000 of the early patents - 2845 of which could be “reconstructed” and re-issued in a “X” format, where the “X” preceded the patent number.  What the Patent Office now considers patent No.1 goes to J. Ruggles, for the design of a traction wheel for locomotive engines. (4)  The Patent Office has TIFF pictures of the patents issued prior to 1976, after that, you can get both a text synopses and TIFF pictures of the patents.  It’s a most interesting way to spend time on the internet.  The only problem is that you can’t do a text search on the old (pre 76) patents since they exist only as images.

In looking thru some of the patents issued in modern times, it seems that inventors are still coming up with interesting ideas that never make it into the real world.  Take for instance, patent No. 4,073, 453 from Feb 1978.  Marion Thomas of Baton Rouge LA came up with an idea for grade crossing protection that overcame the inherent disadvantage of having only a bulb that flashes when the train was coming.  It was a mechanical nightmare that involved motors and gears to make two discs spin around the blinking light.  Another invention that never hit the big-time was No. 4.067,522 from Jan 1978.  Orie Williams of Evansville IN came up with a foot pedal to activate the bell and whistle of a locomotive at the same time.  One “recent” patent from Oct 1989 that may have been used was No. DES. 304,039 by two guys from Louisville KY – it is a warning sign that attaches to the rail head.  I’ve seen blue flag type signs that attach this way to the railhead, so I wonder if these flags use this patent?

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1        http://www.sh1.org/eisenbahn/sac.htm   A rather humorous analysis of Canadian and North American railroad signaling by Wolfgang Meyenberg (more of his stuff on index page)

2        http://www.du.edu/~etuttle/rail/sigs.htm  Good primer on mainly British railroad Signals, some American references

3        http://www.uspto.gov/web/offices/ac/ahrpa/opa/kids/special/1836fire.htm the great fire of 1836

4        webpage for patent search

5        http://www.railserve.com/Equipment/Signals/ Many signal and communications links

6        Quick primer from Trains magazine

7        http://en.wikipedia.org/wiki/Railway_signaling Quick primer from Wikepedia

8        http://www.catskillarchive.com/rrextra/sdbk.Html Scientific American article from 1890

9        http://www.catskillarchive.com/rrextra/Page0002.Html All around reference on old trains, etc

10      http://www.alpharail.net/corp/signals/sigmaint/Signal3.htm Tour of CORP’s signal system

11      http://broadway.pennsyrr.com/Rail/Signal/learning_the_aspects.html  Primer on US signaling by Mark Bej

Links without the blue stuff have been deleted or moved since I originally compiled this list, unfortunate.

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NEW 05/07/2007
Last Modified: 08/26/2013