Talk:Track circuit

Merge from track circuits
This article is duplicated by Track circuits.

Tabletop 03:30, 20 Jun 2005 (UTC)


 * They do indeed cover the same topic. I've added mergeto and mergefrom to both articles suggesting that this article be the final destination (following WP:MOS for the article title). slambo 18:17, 17 October 2005 (UTC)
 * Merge --Soumyasch 06:04, 25 February 2006 (UTC)
 * Merge to Track circuit--Lordkinbote 09:32, 7 March 2006 (UTC)


 * Merge I agree that they should be merged, however I've always heard the term Track circuits used in industry and would suggest flipping the merge-to and merge-from tags. Skabat169 14:29, 17 April 2006 (UTC)
 * Obvious merge — Omegatron 16:20, 23 April 2006 (UTC)
 * Merge - Birdhurst 00:29, 26 April 2006 (UTC)


 * It seems this has already been done; therefore, the above discussion should be archived. 69.140.164.142 05:14, 6 April 2007 (UTC)

Merge from Rail circuits
Yet another duplication of efforts. Slambo (Speak) 13:28, 29 August 2006 (UTC) Merge - User:AdrianSavage 20:00, 30 August 2006 (BST)
 * Merge Slambo (Speak) 13:28, 29 August 2006 (UTC)
 * Don't merge - In UK terminology at least, the two things are different. A track circuit has a normally energised relay. The train's wheels short out the circuit, de-energising the relay. A rail circuit has a normally de-energised relay. The train's wheels complete the circuit and energise the relay. Therefore, a track circuit proves the absence of a train, while a rail circuit proves the presence of a train. 81.79.89.122 17:40, 6 October 2006 (UTC)
 * Comment It's exceedingly hard to check this through a search, but evidence seems to suggest that this is not so. Having come across the 1911 Brittanica article on "signals" I find that it describes "track circuits" in the modern normally-energized form, and also uses the phrase "rail circuit" more or less interchangeably. Mangoe 18:23, 6 October 2006 (UTC)
 * The definitions I gave above are supported by Railway Group Guidance Note GK/GN0802 "Glossary of Signalling Terms", available on the RSSB website at: http://www.rgsonline.co.uk/docushare/dsweb/Get/Rail-27026/gn0802.PDF 62.136.37.250 19:50, 6 October 2006 (UTC)
 * Merge - I believe that the "Rail Circuits" should be merged into "Track Circuit," as track circuit is the most common term for the system, and is IMO the better of the two articles. (BTW, this talk page is very confusing, so idk if I'm even posting this under the correct header) TNLTRPB 04:37, 3 December 2006 (UTC)
 * Merge - Although the above user who says dont merge has a valid objection, that the rail circuits and track circuits are different in a way, but they can be covered under one single heading as we all know that WIKIpedia is not a dictonary, that every item should be covered seperately they can be covered under the same heading as they necessarily provide the same information and different sub headings can be defined. --Psghai 08:52, 1 February 2007 (UTC)

Another merge
This time it's poor shunting, which is simply one bit under "circuit failures".

On a related note: we seem to be trying to grow a list of accidents. I can see leaving the Cowan rail crash as it is an example of a failure mode, though I would incorporate it into the main text rather than letting it sit out in a list. Listing accidents which the presence of track circuits would have prevented strikes me as dubious (since it could be expanded to encompass every 19th century collision) and speculative. Mangoe 13:53, 29 September 2006 (UTC)
 * I agree. I was just looking at poor shunting myself and wondering why it existed.  I was also amused that it says that poor shunting is something that affects railroad signalling in North America and the UK, then provides one real-life example&mdash;from Australia!  Philip J. Rayment 13:58, 29 September 2006 (UTC)

Another type of sabotage is to connect rails with a wire. If this wire is hidden in the ballast, it takes rather long time (a couple of hours) to find it. There was such accident in Russia, possibly (but nobody was found and tried) a bad Fool day's joke of students of a near technical institute.--87.251.146.89 11:09, 3 October 2006 (UTC)

The Big Bayou Canot wreck is not an example of track circuit failure as such, the track circuit is not intended to detect a misaligned rail so it did not fail. —Preceding unsigned comment added by 86.132.198.82 (talk) 07:19, 24 September 2007 (UTC)

The examples of accidents due to 'broken rails' are a bit tenuous. Firstly this is an article about track circuits and despite the track engineers best hopes, the primary purpose of track circuits is not to detect broken rails. The two examples prove this by both being undetected by track circuits - Hither Green saw the head of the rail damaged but the rail web was unbroken and therefore would not have been detected by track circuits. The accident at Weyauwega saw a break within the crossing in a position that would be most likely parallel bonded and therefore would be undetected. I suggest removing both of these 23.101.225.195 (talk) 05:44, 6 May 2019 (UTC)

Battery circuit accuracy
I assume the battery circuits shown in the diagrams are simplified versions, only meant as indicative. Even so, I think the battery should be shown with a current-limiting, series resistor. In the short circuit condition, the battery or power supply (as shown) would fail. Looking at such a schematic melts my brain.

216.165.154.93 00:19, 6 November 2006 (UTC) [JM]


 * You are quite right. There should be a resistor at the battery end. A recent book on signalling places this resistor at the wrong or relay end!


 * Seconded. The resistor should be shown.   Tabletop (talk) 03:15, 12 December 2008 (UTC)

Track circuit
Having worked on railroads in several areas of the world (in my early days I was a signal maintainer), the only term I have consistently heard to describe a track circuit is, in fact, track circuit. All information regarding track circuits should, in my opinion, be coalesced into a single article titled Track Circuits.

Also, the article, as presently written, confuses signal operation with track circuit operation, which are mutually independent functions. All a track circuit does is indicate the presence or absence of a train in a given stretch of track. The use of that information has no relationship to the track circuit itself (in fact, most designs carefully isolate a track circuit from what it controls to maximize reliability). A track circuit could control block signals, operate grade crossing signals, set up first-come, first-served interlocking, turn on station platform lights and annunciate the approach of a train to passengers waiting in a station...you get my drift.

BDD 22:15, 23 February 2007 (UTC)

Track Relay
Track relays are designed with the coil in a "vertical" position and the armature contacts at bottom of coil. When there is no current flowing through the coil, the contacts "drop" down, to display an "occupied/red" signal, provided lightning or some other anomaly has not fused the points together in the "clear/green" position. A interesting fact, "Gravity never fails" in regards to the relay contacts dropping downward.

User: Lairbear 16:45, 29 AUG 2010 (UTC) —Preceding unsigned comment added by 75.37.139.108 (talk)

Clapham Junction
I see my addition of this accident has been removed; I'd like to discuss this. The accident occurred because a track-circuit relay had been shorted out, and relay failure is listed as one of the possible causes of track-circuit failure in the article. True, it was a fault in the _wiring_ rather than the actual _relay_, if that's the issue; but I don't really think that's where we should draw the line between a track-circuit failure and (presumably) a signal failure. The signalling system worked as designed, it just wasn't being fed the correct inputs from the track-circuit system, insofar as the two systems could be conceptually seperated at Clapham Junction. If my interpretation of the removal is incorrect, of course, I'd like to know what the criteria for a track-circuit failure are that Clapham Junction fails to meet. Tevildo (talk) 20:10, 25 August 2008 (UTC)
 * It was me who removed the reference to Clapham. A track circuit begins with the feed and ends at the track circuit relay. At Clapham Junction, all the track circuit relays associated with any occupied sections of line were correctly de-energised, therefore the track circuits were working correctly. As you've said yourself, it was a wiring problem that led to the accident.
 * P.S. "separated", not "seperated". – Signal head   &lt; T &gt;  20:34, 25 August 2008 (UTC)
 * OK. I wouldn't personally have drawn the line there, but if that's the consensus, I won't dispute it.
 * PS. "It was I", not "It was me". Tevildo (talk) 20:54, 25 August 2008 (UTC)


 * A key factor in the Clapham accident was the lack of double switching.

Snow and Ice?
How badly are track circuits affected by snow and ice (compared to say sand and rust)?

Tabletop (talk) 11:43, 25 December 2008 (UTC)


 * Snow and ice are seldom problems due to the unit loading that occurs at the interface of wheel and rail&mdash;the snow and/or ice will be liquified and force out. Rust can be a problem and may result in failure to shunt, creating a potentially deadly condition.

Bigdumbdinosaur (talk) 18:22, 9 January 2009 (UTC)

Relays
"Track circuit relays are specially designed to reduce the chance of wrong side failures. They might for example have carbon-silver contacts to reduce the likelihood of the wrong contacts welding shut after power surges and lightning strikes."


 * In French relay practice, IIRC, they use silver-silver contacts.

- Does that really need to be stated in this article? In British practice, all relays in vital signalling circuits have carbon-silver contacts to minimise risk of wrong side failure.– Signal head   &lt; T &gt;  17:55, 29 May 2009 (UTC)

On the relay front, there's the infamous GRS cadmium screw debacle.. General Railway Signal used cadmium-plated screws in type B1 vital relays from 1960 to 1985, and those would corrode and stick to the core head surface. All those relays were supposed to be replaced. This was a big deal; it was very expensive, and some lines, including the Washington Metro, had to run at reduced speeds on manual until the relays were replaced. Transport Canada has a good writeup on this.. --John Nagle (talk) 06:06, 25 June 2009 (UTC)

Circuits under electrification
What does this mean? ''In some countries, AC-immune DC track circuits are used on AC electrified lines. One method provides 5 V DC to the rails, one of the rails being the traction return and the other being the signal rail. When a relay is energised and attached to the track, normal voltage is 5 V DC. When there is a break in the circuit and there is no train, the voltage rises to 9 V DC which provides a very good means for fault finding. This system filters out the voltage induced in the rails from the overhead lines.''

9 volts and 5 volts relative to what? How is the circut made? 86.141.233.251 (talk) 13:21, 16 April 2012 (UTC)


 * Also I would think it preferable for both tracks to carry traction return current to reduce losses.

The track circuit block sections would be isolated with impedance bonds for which Wikipedia has no article 86.141.233.251 (talk) 16:18, 16 April 2012 (UTC)

Jointless tracks circuits is confusing
I'm an electrical engineer, but I can't make sense of this section. It immediately jumps into details of specific commercial products after an inadequate introduction. Somebody who understands this topic should write a longer, clearer introduction followed by more explanation and less jargon. I came here to learn, so I'm not the one. This is written more like a technical presentation than an encyclopedia article. Will any uninformed general reader know what "This can be extended to 2200 m with compensating capacitors." means? Robsavoie (talk) 20:07, 5 June 2011 (UTC)

I am a track circuit expert. I originally updated some of the section on jointless TCs to clarify what had already been written.

The comments above are valid and as time permits I will attempt to introduce the topic in a more encyclopaedic style. BaronVonQuattro (talk) 21:21, 10 April 2012 (UTC)


 * I have similar problems.

To prevent the audio signal from one section passing into an adjacent section, a simple tuned circuit is connected across the rails at the section boundary

How does it do this? 86.141.233.251 (talk) 13:21, 16 April 2012 (UTC)

Some popular AF track circuits used in the UK
''Frequencies of the Aster SF 15 type track circuit are 1700 Hz and 2300 Hz on one track and 2000 Hz and 2600 Hz on the other. ''

What track and what other?

''The lack of modulation can lead to availability problems as well as making the signalling safety case difficult to produce. ''

What? Why?

''To simplify traction pack design in locomotives, many track circuit manufacturers now transmit a unique code from the transmitter to the receiver. ''

Whay would you need a traction pack in the loco if all the system is for is inform the signaller of the presence or absence of a train in the section.?

I think that's all for now. THanks 86.141.233.251 (talk) 13:21, 16 April 2012 (UTC)

Siding Turnout
If this exists anywhere in the world, I suspect it is rare. One of the basic principles of point locking in all the countries I've worked is to disable movement if the track section over it is occupied - thus dropping the track if the points are reverse would lock them permanently! At the very least, citations are required to make this less dubious. — Preceding unsigned comment added by 108.23.115.151 (talk) 20:57, 21 September 2015 (UTC)
 * If this dubious info is not true, then I propose a Db-G3 eval.Lomrjyo 03:01, 20 May 2018 (UTC) — Preceding unsigned comment added by Lomrjyo (talk • contribs)

Lac-Mégantic rail disaster
I’ve read the CTSB report on this wreck. No blame for the wreck was assigned to signalling and/or track circuits. This wreck should not be in the list of wrecks attributable to signalling failure.


 * 216.152.18.132 (talk) 08:04, 11 March 2023 (UTC)


 * The line was unsignaled so yeah.Sturmovik (talk) 13:25, 15 March 2023 (UTC)

Poor terminology
The reference to ‘isolated’ track circuits ought to use a different term (individual?) In CIRCUITS UNDER ELECTRIFICATION paragraph 4 Andyeff (talk) 12:57, 2 February 2024 (UTC)