From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Trains (Rated Start-class, Mid-importance)
WikiProject icon This article is within the scope of WikiProject Trains, an attempt to build a comprehensive and detailed guide to rail transport on Wikipedia. If you would like to participate, you can visit the project page, where you can join the project and/or contribute to the discussion. See also: WikiProject Trains to do list
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 Mid  This article has been rated as Mid-importance on the project's importance scale.
Note icon
This article lacks sufficient references and/or adequate inline citations.

What are the odds?[edit]

Slambo: What are the odds

  • that when I visited Wikipedia's Interlocking page, that I discover that the image illustrating the article is of the very same interlocking tower I grew up near and spent time visiting?
  • that, when I searched my photo archives for images to illustrate the locking machinery, it dawned on me that my best image was of the same tower?

Small world, eh?

By the way, I updated the opening paragraph per your suggestion. The definition that appears there is a typical railroad definition of interlocking; I didn't provide attribution because there are so many unpublished sources (railroad rule books and the like) that make the same or similar definition. Regards. — JonRoma 18:25, 21 January 2006 (UTC)

Indeed. That's the only tower that I've actually visited (although I never got to look inside). I'm a little farther north now, but still within range for a day trip. Slambo (Speak) 19:45, 21 January 2006 (UTC)
Sadly, Deval Tower closed during 2005 after an electrical fire damaged the 1910-vintage interlocking machine to the degree where it could not economically be repaired. The plant is now remote-controlled, though the tower still stands and is used by railroad maintenance forces. I'm glad I took lots of photos inside and around before it closed. — JonRoma 20:03, 21 January 2006 (UTC)

An image like this one would be great[edit]

Something like [1] would be useful for understanding the concept of a mechanical interlocking. --NE2 22:07, 12 February 2007 (UTC)

But that picture doesn't show any interlocking; it's just a load of rodding and cranks. A better picture would be one like this: [2] which the article already has. A diagram might help to clarify things too. Signalhead 22:22, 12 February 2007 (UTC)
It shows one part of the system - the connection between the board and the tracks. --NE2 22:57, 12 February 2007 (UTC)
It might be more relevant to an article on mechanical signalling. I'm sure I have a similar photo of my own that could be used, were such an article to be written. Signalhead 23:08, 12 February 2007 (UTC)
This article mentions those: "In purely mechanical plants, the levers operate the field devices, such as signals, directly via a mechanical rodding or wire connection." --NE2 23:16, 12 February 2007 (UTC)
There is also the lever frame article, which mentions the rods and wires as well. I just feel that an article on interlocking isn't the most appropriate place to discuss the connections to the outside apparatus, as that doesn't form part of the interlocking. Signalhead 23:34, 12 February 2007 (UTC)

Not solid state[edit]

Modern interlocking in germany (as implemented by Siemens and SEL) is operating on special general purpose computers. These work with a 2-out-of-3 logic in software. Any command will only be obeyed too after two out of three of the computers issue essentually the same command. Therefore any command will be analysed before, that the numbers of the issuing computers in the telegram are different and not equal to 0 (zero), redundancy bits in the telegram must be correct. These programs have to be approved by the german institution called Eisenbahn-Bundesamt. Both providers use different computer hardware bought "off the shelve". So its not solid state - its software only. --SonniWP 13:55, 12 June 2007 (UTC)

interlang link[edit]

Interlang links about this article are very confusing, I think. Japanese ja:連動装置 means interlocking machines, so this is correct. However, German de:Stellwerk means signal box. I'm not familiar with other languages, but they seem to be incorrect. The edit of 19:19, 19 June 2008 UTC modified some interlang links, but it made things more confusing. The article before the edit had linked to German de:Streckenblock, but this means block system. I know that English Wikipedia already have Automatic Block Signal, but I think enwp needs a general article about railway block system (including non-automatic block system like token system). Then, the article can be linked to de:Streckenblock. Can anyone write such an article?--Tam0031 (talk) 16:38, 1 July 2008 (UTC)

In German, de:Stellwerk means signal box (the building) as well as interlocking (the machinery). So that link is fine.haraldmmueller 14:00, 24 November 2012 (UTC) — Preceding unsigned comment added by Haraldmmueller (talkcontribs)

International history section[edit]

Added some information and image from Canada and removed the Globalize/USA|date=August 2008 tag. There are also images for signals in the UK and germany on wikimedia commons which may be appropriate here... signal boxes Kind Regards SriMesh | talk 03:04, 7 October 2008 (UTC)

Am I correct in saying that a large number of countries used railway signalling equipment derived from equipment designed by either US and UK companies, or am I neglecting continental Europe? Wongm (talk) 10:42, 7 October 2008 (UTC)
To be honest, I don't see what this Oban, Saskatchewan image adds to the article. There is already one photograph of an interlocking tower (an operational one, not a defunct one in a museum), but actually this article concerns the interlocking equipment housed inside, not the building itself. I see that the same image has been added to a few other articles as well. Could this be an attempt to promote a particular museum or preservation project on Wikipedia? –Signalhead < T > 16:50, 7 October 2008 (UTC)

What preceded interlocking?[edit]

How did railroads prevent track conflicts and collisions prior to the development of interlocking systems? In other words, what system did interlocking replace? --Badger151 (talk) 13:56, 13 January 2010 (UTC)

Nothing preceded interlocking. It was entirely the responsibility of the signalman (to use the British term) not to signal a train to proceed without first checking that the points/switches were correctly set.–Signalhead < T > 17:49, 13 January 2010 (UTC)
So, the point of interlocking is to be sure that the points (switches) are properly aligned, but not to be sure that other trains aren't on the same track? I'm thinking in terms of things like the token system. --Badger151 (talk) 19:58, 14 January 2010 (UTC)
That's about right (in modern interlocking systems, proving that the line is clear may also be considered as a function of the interlocking). The token system is an example of a block system, the primary function of which is to prove that the line is clear (between one interlocking area and the next).–Signalhead < T > 23:23, 14 January 2010 (UTC)
Thanks! --Badger151 (talk) 14:48, 15 January 2010 (UTC)
In "traditional" systems, like a conventional double-track arrangement which consisted of one track signaled in each direction, the interlocking's function was only to ensure that the route through the interlocking is intact and is not in conflict with any other route established through the plant. Separation between trains moving in the same direction was typically provided with some form of a block system, be it the British absolute block system or automatic block signaling such as that typically used in the U. S.
Other than preventing conflicting moves within the same plant, and other than providing block indications when an interlocking signal was part of a block system, it was not within the purview or capability of an interlocking on this type of double-track arrangement to cross-check with the next interlocking in advance. Because of this limitation, wrong-direction moves required some other form of authority. In North America, this was typically done via a written train order which required the interlocking tower operator to hold opposing trains clear of the section to be used in the wrong direction, and which simultaneously gave a train the authority to operate in the wrong direction.
There is, however, a principle called traffic locking that was developed around the turn of the Twentieth century. This provides a fail-safe means of establishing direction on a track between adjacent interlocking plants. This eliminates the written train order and provides a way to give authority to train movements solely with signal indication. This principle is a key component of Centralized Traffic Control.
JonRoma (talk) 18:00, 20 September 2010 (UTC)

Complete and incomplete interlockings (U.S. terminology)[edit]

Where did this section come from? I have never heard this term used among any of the several signal engineers or civil engineers I know. Even if it is an accepted term, it has little to do with the actual subject of this article. JonRoma (talk) 17:40, 20 September 2010 (UTC)

History removal[edit]

I removed the history section at all as it dealt exclusively with US, while the argument is largely international. --'''Attilios''' (talk) 23:56, 14 January 2011 (UTC)

I restored parts of the History section after rewriting to give more of an international flavor. The first paragraph continues to cover the pioneering installations in the UK, but most of the rest refers to North American installations, albeit installed by companies now with European parentage. Other editors are urged to expand the coverage globally (e.g., as in Railway switching networks). Early history is an essential part of the Interlocking article, and this section takes the reader from pure mechanical systems through hydro-mechanical and electro-mechanical to all-electric systems; however, the latest reference is 1913. Knowledgeable editors are welcome to bring the time line forward from relay logic through solid state components and now to computer-based systems. (NB: modern systems are discussed in some detail in subsequent sections.) Casey (talk) 03:56, 28 October 2011 (UTC)


This article needs to use more examples, terminology & sources from outside the US. Not that it isn't good, it just sounds like a US guide to signal interlocking. Archolman User talk:Archolman 21:44, 25 October 2011 (UTC)