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subsection</span> </button> <ul id="toc-Principles_and_operation-sublist" class="vector-toc-list"> <li id="toc-Basic_circuit" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Basic_circuit"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>Basic circuit</span> </div> </a> <ul id="toc-Basic_circuit-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Circuits_under_electrification" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Circuits_under_electrification"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Circuits under electrification</span> </div> </a> <ul id="toc-Circuits_under_electrification-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Jointless_track_circuits" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Jointless_track_circuits"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3</span> <span>Jointless track circuits</span> </div> </a> <ul id="toc-Jointless_track_circuits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-CSEE_UM71" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#CSEE_UM71"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.4</span> <span>CSEE UM71</span> </div> </a> <ul id="toc-CSEE_UM71-sublist" class="vector-toc-list"> <li id="toc-Data_pickup_unit" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Data_pickup_unit"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.4.1</span> <span>Data pickup unit</span> </div> </a> <ul id="toc-Data_pickup_unit-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-DC_coded_track_circuits" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#DC_coded_track_circuits"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.5</span> <span>DC coded track circuits</span> </div> </a> <ul id="toc-DC_coded_track_circuits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Cut_tracks" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cut_tracks"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.6</span> <span>Cut tracks</span> </div> </a> <ul id="toc-Cut_tracks-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-High-voltage_tracks" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#High-voltage_tracks"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.7</span> <span>High-voltage tracks</span> </div> </a> <ul id="toc-High-voltage_tracks-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Single_rail_and_double_rail" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Single_rail_and_double_rail"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.8</span> <span>Single rail and double rail</span> </div> </a> <ul id="toc-Single_rail_and_double_rail-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Failure_modes_and_prevention" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Failure_modes_and_prevention"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Failure modes and prevention</span> </div> </a> <button aria-controls="toc-Failure_modes_and_prevention-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Failure modes and prevention subsection</span> </button> <ul id="toc-Failure_modes_and_prevention-sublist" class="vector-toc-list"> <li id="toc-Wheels_and_brakes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Wheels_and_brakes"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Wheels and brakes</span> </div> </a> <ul id="toc-Wheels_and_brakes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Relays" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Relays"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>Relays</span> </div> </a> <ul id="toc-Relays-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Circuit_failures" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Circuit_failures"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Circuit failures</span> </div> </a> <ul id="toc-Circuit_failures-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Railhead_contamination_and_rust" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Railhead_contamination_and_rust"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.4</span> <span>Railhead contamination and rust</span> </div> </a> <ul id="toc-Railhead_contamination_and_rust-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Scale" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Scale"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.5</span> <span>Scale</span> </div> </a> <ul id="toc-Scale-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Immunization" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Immunization"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.6</span> <span>Immunization</span> </div> </a> <ul id="toc-Immunization-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Transitory_problems" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Transitory_problems"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.7</span> <span>Transitory problems</span> </div> </a> <ul id="toc-Transitory_problems-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Siding_turnout" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Siding_turnout"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Siding turnout</span> </div> </a> <ul id="toc-Siding_turnout-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Track-circuit_operating_clips" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Track-circuit_operating_clips"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Track-circuit operating clips</span> </div> </a> <ul id="toc-Track-circuit_operating_clips-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>History</span> </div> </a> <ul id="toc-History-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Accidents" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Accidents"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Accidents</span> </div> </a> <button aria-controls="toc-Accidents-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Accidents subsection</span> </button> <ul id="toc-Accidents-sublist" class="vector-toc-list"> <li id="toc-Caused_by_lack_of_track_circuits" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Caused_by_lack_of_track_circuits"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Caused by lack of track circuits</span> </div> </a> <ul id="toc-Caused_by_lack_of_track_circuits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Caused_by_track_circuit_failure" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Caused_by_track_circuit_failure"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>Caused by track circuit failure</span> </div> </a> <ul id="toc-Caused_by_track_circuit_failure-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Broken_rails" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Broken_rails"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.3</span> <span>Broken rails</span> </div> </a> <ul id="toc-Broken_rails-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Track circuit</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. 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href="https://cs.wikipedia.org/wiki/Kolejov%C3%BD_obvod" title="Kolejový obvod – Czech" lang="cs" hreflang="cs" data-title="Kolejový obvod" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Gleisfreimeldeanlage#Gleisstromkreis" title="Gleisfreimeldeanlage – German" lang="de" hreflang="de" data-title="Gleisfreimeldeanlage" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Circuito_de_v%C3%ADa" title="Circuito de vía – Spanish" lang="es" hreflang="es" data-title="Circuito de vía" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Circuit_de_voie" title="Circuit de voie – French" lang="fr" hreflang="fr" data-title="Circuit de voie" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Circu%C3%ADto_de_v%C3%ADa" title="Circuíto de vía – Galician" lang="gl" hreflang="gl" data-title="Circuíto de vía" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EA%B6%A4%EB%8F%84_%ED%9A%8C%EB%A1%9C" title="궤도 회로 – Korean" lang="ko" hreflang="ko" data-title="궤도 회로" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Circuito_di_binario" title="Circuito di binario – Italian" lang="it" hreflang="it" data-title="Circuito di binario" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Spoorstroomloop" title="Spoorstroomloop – Dutch" lang="nl" hreflang="nl" data-title="Spoorstroomloop" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E8%BB%8C%E9%81%93%E5%9B%9E%E8%B7%AF" title="軌道回路 – Japanese" lang="ja" hreflang="ja" data-title="軌道回路" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link 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class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%A7%E0%B8%87%E0%B8%88%E0%B8%A3%E0%B9%84%E0%B8%9F%E0%B8%95%E0%B8%AD%E0%B8%99" title="วงจรไฟตอน – Thai" lang="th" hreflang="th" data-title="วงจรไฟตอน" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A0%D0%B5%D0%B9%D0%BA%D0%BE%D0%B2%D0%B5_%D0%BA%D0%BE%D0%BB%D0%BE" title="Рейкове коло – Ukrainian" lang="uk" hreflang="uk" data-title="Рейкове коло" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E8%BD%A8%E9%81%93%E7%94%B5%E8%B7%AF" title="轨道电路 – Chinese" lang="zh" hreflang="zh" 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class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Electrical device used to detect the presence of trains on rail tracks</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">This article is about an electrical device used on railways. For racecourses, see <a href="/wiki/Race_track" title="Race track">race track</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Track_circuit" title="Special:EditPage/Track circuit">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Track+circuit%22">"Track circuit"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Track+circuit%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Track+circuit%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Track+circuit%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Track+circuit%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Track+circuit%22&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">June 2009</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Track_circuit_Robinson_1874.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/82/Track_circuit_Robinson_1874.jpg/220px-Track_circuit_Robinson_1874.jpg" decoding="async" width="220" height="127" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/82/Track_circuit_Robinson_1874.jpg/330px-Track_circuit_Robinson_1874.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/82/Track_circuit_Robinson_1874.jpg/440px-Track_circuit_Robinson_1874.jpg 2x" data-file-width="1296" data-file-height="746" /></a><figcaption>Illustration of track circuit invented by William Robinson in 1872</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Izolirka.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/92/Izolirka.jpg/220px-Izolirka.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/92/Izolirka.jpg/330px-Izolirka.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/92/Izolirka.jpg/440px-Izolirka.jpg 2x" data-file-width="4032" data-file-height="3024" /></a><figcaption>Track circuit transformer on the right, new axle counter on the left (Slovenia).</figcaption></figure> <p>A <b>track circuit</b> is an electrical device used to prove the absence of a <a href="/wiki/Train" title="Train">train</a> on <a href="/wiki/Rail_tracks" class="mw-redirect" title="Rail tracks">rail tracks</a> to signallers and control relevant signals. An alternative to track circuits are <a href="/wiki/Axle_counter" title="Axle counter">axle counters</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Principles_and_operation">Principles and operation</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=1" title="Edit section: Principles and operation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The basic principle behind the track circuit lies in the connection of the two rails by the wheels and axle of <a href="/wiki/Locomotive" title="Locomotive">locomotives</a> and <a href="/wiki/Rolling_stock" title="Rolling stock">rolling stock</a> to short an electrical circuit. This circuit is monitored by electrical equipment to detect the absence of the trains. Since this is a safety appliance, <a href="/wiki/Fail-safe" title="Fail-safe">fail-safe</a> operation is crucial. Hence the circuit is designed to indicate the presence of a train when failures occur. On the other hand, false occupancy readings are disruptive to railway operations and must be minimized. </p><p>Track circuits allow <a href="/wiki/Railway_signalling" title="Railway signalling">railway signalling</a> systems to operate semi-automatically, by displaying signals for trains to slow or stop in the presence of occupied track ahead of them. They help prevent <a href="/wiki/Train_dispatcher" title="Train dispatcher">dispatchers</a> and <a href="/wiki/Manual_block" class="mw-redirect" title="Manual block">operators</a> from causing accidents, both by informing them of track occupancy and by preventing signals from displaying unsafe indications. </p> <div class="mw-heading mw-heading3"><h3 id="Basic_circuit">Basic circuit</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=2" title="Edit section: Basic circuit"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Clear_track_circuit.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/07/Clear_track_circuit.svg/220px-Clear_track_circuit.svg.png" decoding="async" width="220" height="136" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/07/Clear_track_circuit.svg/330px-Clear_track_circuit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/07/Clear_track_circuit.svg/440px-Clear_track_circuit.svg.png 2x" data-file-width="714" data-file-height="442" /></a><figcaption>Schematic drawing of track circuit for unoccupied block<br /> (series resistor next to battery not shown)</figcaption></figure> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Occupied_track_circuit.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Occupied_track_circuit.svg/220px-Occupied_track_circuit.svg.png" decoding="async" width="220" height="136" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Occupied_track_circuit.svg/330px-Occupied_track_circuit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Occupied_track_circuit.svg/440px-Occupied_track_circuit.svg.png 2x" data-file-width="714" data-file-height="442" /></a><figcaption>Schematic drawing of occupied track circuit<br /> (series resistor next to battery not shown)</figcaption></figure> <p>A track circuit typically has power applied to each rail and a <a href="/wiki/Relay" title="Relay">relay</a> coil wired across them. When no train is present, the relay is energised by the current flowing from the power source through the rails. When a train is present, its axles short (<a href="/wiki/Shunt_(electrical)" title="Shunt (electrical)">shunt</a>) the rails together. The current to the track relay coil drops, and it is de-energised. Circuits through the relay contacts therefore report whether or not the track is occupied. </p><p>Each circuit detects a defined section of track, such as a <a href="/wiki/Railway_signalling#Blocks" title="Railway signalling">block</a>. These sections are separated by insulated <a href="/wiki/Jointed_track" class="mw-redirect" title="Jointed track">joints</a>, usually in both rails. To prevent one circuit from falsely powering another in the event of insulation failure, the <a href="/wiki/Electrical_polarity" class="mw-redirect" title="Electrical polarity">electrical polarity</a> is usually reversed from one section to an adjacent section. Circuits are powered at low voltages (1.5 to 12 V DC). The relays and the power supply are attached to opposite ends of the section to prevent broken rails from electrically isolating part of the track from the circuit. A series <a href="/wiki/Resistor" title="Resistor">resistor</a> limits the current when the track circuit is short-circuited. </p> <div class="mw-heading mw-heading3"><h3 id="Circuits_under_electrification">Circuits under electrification</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=3" title="Edit section: Circuits under electrification"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In some <a href="/wiki/Railway_electrification" title="Railway electrification">railway electrification</a> schemes, one or both of the running rails are used to carry the return traction current. This precludes use of the basic DC track circuit because the substantial <a href="/wiki/Traction_motor" title="Traction motor">traction</a> currents overwhelm the very small track circuit currents. </p><p>Where DC traction is used on the running line or on tracks in close proximity then DC track circuits cannot be used; similarly if 50 Hz AC electrification is used then 50 Hz AC track circuits cannot be used. </p><p>To accommodate this, AC track circuits use <a href="/wiki/Alternating_current" title="Alternating current">alternating current</a> (AC) signals instead of <a href="/wiki/Direct_current" title="Direct current">direct current</a> (DC) but typically, the AC frequency is in the range of <a href="/wiki/Audio_frequency" title="Audio frequency">audio frequencies</a>, from 91 Hz up to 10 kHz. The relays are arranged to detect the selected frequency and to ignore DC and AC traction frequency signals. Again, fail-safe principles dictate that the relay interprets the presence of the signal as unoccupied track, whereas a lack of a signal indicates the presence of a train. The AC signal can be coded and locomotives equipped with inductive pickups to create a <a href="/wiki/Cab_signalling" title="Cab signalling">cab signalling</a> system. </p><p>There are two common approaches to provide a continuous path for traction current that spans multiple track circuit blocks. The simplest method installs insulated track circuit joints on only one of the two rails with the second being a path for the return current and a ground for the track circuit rail. This has the disadvantage of only being able to detect breaks in one rail so the more popular two rail system uses <a href="/wiki/Electrical_impedance" title="Electrical impedance">impedance</a> bonds to permit traction current to pass between isolated track circuit blocks while blocking current at track circuit frequencies. </p><p>AC circuits are sometimes used in areas where conditions introduce stray currents, which interfere with DC track circuits. </p> <div class="mw-heading mw-heading3"><h3 id="Jointless_track_circuits">Jointless track circuits</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=4" title="Edit section: Jointless track circuits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1237032888/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:312px;max-width:312px"><div class="trow"><div class="tsingle" style="width:84px;max-width:84px"><div class="thumbimage" style="height:108px;overflow:hidden"><span typeof="mw:File"><a href="/wiki/File:A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4f/A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg/82px-A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg" decoding="async" width="82" height="109" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4f/A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg/123px-A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4f/A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg/164px-A_local_variant_of_the_GRS_Wee-Z_Bond_at_Jinjiang_Park_Station.jpg 2x" data-file-width="1951" data-file-height="2585" /></a></span></div></div><div class="tsingle" style="width:224px;max-width:224px"><div class="thumbimage" style="height:108px;overflow:hidden"><span typeof="mw:File"><a href="/wiki/File:S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/94/S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg/222px-S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg" decoding="async" width="222" height="108" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/94/S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg/333px-S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/94/S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg/444px-S-Bond_of_an_Alstom_Digicode_track_circuit_at_Shanghai_Railway_Station_of_Metro_Line_3.jpg 2x" data-file-width="4032" data-file-height="1960" /></a></span></div></div></div><div class="trow" style="display:flex"><div class="thumbcaption">Electric "joints" of jointless track circuits on <a href="/wiki/Shanghai_Metro" title="Shanghai Metro">Shanghai Metro</a>. Left: Wee-Z Bond of a <a href="/wiki/General_Railway_Signal" title="General Railway Signal">GRS</a> audio frequency track circuit; Right: S-Bond of an <a href="/wiki/Alstom" title="Alstom">Alstom</a> Digicode track circuit</div></div></div></div> <p>Modern track is often <a href="/wiki/Continuous_welded_rail" class="mw-redirect" title="Continuous welded rail">continuously welded</a>, the joints being welded during installation. This offers many benefits, except to the signalling system, which no longer has natural breaks in the rail to form block sections. The only method to form discrete blocks in this scenario is to use different audio frequencies (AF) in each block section. To prevent the audio signal from one section passing into an adjacent section, pairs of <a href="/wiki/Tuned_circuit" class="mw-redirect" title="Tuned circuit">tuned circuits</a> are connected across the rails at the section boundary. The tuned circuit often incorporates the circuit to either apply the transmitted signal to the track or recover the received signal from the other end of the section. </p><p>Consider a railway with two block sections as in the diagram. Section 1 has frequency A injected at the left-hand end and received at the right-hand end. Section 2 continues from the right hand end of section 1 where frequency B is injected and then received at the right-hand end of section 2. </p> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Track_circuit_tuned_zone.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/en/thumb/5/5a/Track_circuit_tuned_zone.gif/220px-Track_circuit_tuned_zone.gif" decoding="async" width="220" height="193" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/5/5a/Track_circuit_tuned_zone.gif/330px-Track_circuit_tuned_zone.gif 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/5/5a/Track_circuit_tuned_zone.gif/440px-Track_circuit_tuned_zone.gif 2x" data-file-width="624" data-file-height="546" /></a><figcaption>Track circuited railway with two block sections</figcaption></figure> <p>There is often a gap between where frequency A is received and frequency B is injected. This is referred to as a 'tuned zone' and is a section of track where the amplitude of frequency A reduces in the direction of section 2 and the amplitude of frequency B reduces in the direction of section 1. The tuned zone can be of the order of 20 m long. </p><p>Advantages of jointless track circuits: </p> <ul><li>Eliminates insulated block joints, a component liable to mechanical failure (both of insulation and by introducing stress to adjoining rails) and maintenance.</li> <li>In electrified areas, jointless track circuits require fewer impedance bonds than any other double rail traction return track circuits.</li></ul> <p>Disadvantages of jointless track circuits: </p> <ul><li>Restrictions on placing impedance bonds, hence any connection for electrification purposes, in or near tuned zones as this may upset the filter properties of the tuned zone.</li> <li>Electronic circuits are more vulnerable to lightning strikes.</li></ul> <div class="mw-heading mw-heading3"><h3 id="CSEE_UM71">CSEE UM71</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=5" title="Edit section: CSEE UM71"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/86/The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg/250px-The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg" decoding="async" width="250" height="122" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/86/The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg/375px-The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/86/The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg/500px-The_matching_unit_of_an_ZPW-2000A_track_circuit.jpg 2x" data-file-width="4032" data-file-height="1960" /></a><figcaption>Tuning unit of a ZPW-2000 (Chinese variant of UW71) track circuit and a sign indicating "do not stop at circuit boundary", where loss-of-shunt may occur.</figcaption></figure> <p>CSEE (now <a href="/wiki/Ansaldo_STS" class="mw-redirect" title="Ansaldo STS">Ansaldo STS</a>) UM71 is another kind of jointless track circuit. It uses 1700 Hz and 2300 Hz on one track and 2000 Hz and 2600 Hz on the other.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> To reduce the chance of stray currents causing a <a href="/wiki/Wrong_side_failure" class="mw-redirect" title="Wrong side failure">wrong side failure</a> the modulation frequency is calculated by dividing the base frequency by 128. Different rates of modulation can be detected by equipment on the trains and used for <a href="/wiki/Automatic_train_control" title="Automatic train control">automatic train control</a>, so long as the transmitter end (Tx) is at the front of the train. </p><p>The <b>EBItrack</b> (formerly <b>TI21</b>) and Westinghouse <b>FS2500</b> jointless track circuits are similar to the UM71. </p> <div class="mw-heading mw-heading4"><h4 id="Data_pickup_unit">Data pickup unit</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=6" title="Edit section: Data pickup unit"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:DPU_CSEE_End_View.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/37/DPU_CSEE_End_View.jpg/220px-DPU_CSEE_End_View.jpg" decoding="async" width="220" height="178" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/37/DPU_CSEE_End_View.jpg/330px-DPU_CSEE_End_View.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/37/DPU_CSEE_End_View.jpg/440px-DPU_CSEE_End_View.jpg 2x" data-file-width="515" data-file-height="417" /></a><figcaption>Data pickup unit CSEE; end view</figcaption></figure> <p>A jointless track circuit such as the CSEE can be divided with a <b>data pickup unit</b> (DPU), which is cheaper than splitting it into two track circuits. A DPU avoids the need to change the frequency of a whole series of track circuits in a cascade. The DPU consists of a tuned coil which detects the presence or absence of current in the adjacent rail and picks up or drops a relay accordingly. One use of DPUs is for timing circuits. Each track circuit frequency has its own DPU tuned to that frequency. DPUs can be located almost anywhere; they overcome the limitation that jointless tracks have a minimum length. </p> <div class="mw-heading mw-heading3"><h3 id="DC_coded_track_circuits">DC coded track circuits</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=7" title="Edit section: DC coded track circuits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In non-electrified areas, DC coded track circuits may be used. These modulate the current going from the powersource end to the relay end and control the signals and cab signals without the need for line wires. The modulated currents can be detected by equipment connected to the track to provide signaling and indication information to activate proper <a href="/wiki/Cab_signalling" title="Cab signalling">cab signalling</a> if available. <sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> They can be overlain by predictor systems to operate level crossings.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>Brands of coded track circuit include: </p> <ul><li>Alstom née GE Electrocode 5</li> <li>Microtrax/E-Code by Hitachi née <a href="/wiki/Union_Switch_%26_Signal" title="Union Switch & Signal">Union Switch & Signal</a></li></ul> <div class="mw-heading mw-heading3"><h3 id="Cut_tracks">Cut tracks</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=8" title="Edit section: Cut tracks"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Where the length of a section exceeds the practical length of a track circuit, cut tracks can be provided. With a cut track, the relay of the last track cuts the powersource feed of the second last track circuit, and so on. Cut tracks are only suitable for unidirectional tracks. </p><p>Track circuits with ballast contamination will be shorter than those with good ballast, thus needing more cut tracks. </p> <div class="mw-heading mw-heading3"><h3 id="High-voltage_tracks">High-voltage tracks</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=9" title="Edit section: High-voltage tracks"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>One common brand of high-voltage impulse track (HVIT) circuit is made by <a href="/wiki/Jeumont-Schneider" title="Jeumont-Schneider">Jeumont-Schneider</a>. The high voltage penetrates rust and other problems. </p><p>The HVIT transmits two pulses alternately, a narrow positive one at about 100 V DC and a negative broader one at about 30 V DC. The energy of the two pulses is the same. At the receiver end an R-C circuit integrates the two pulses, which must be of the correct proportions for the relay to pick up. The R-C circuits check that the positive and negative pulses are in correct phase. The two pulses operate at about 1 Hz. </p><p>The circuit operates on AC and DC electrified lines, with additional equipment. </p> <div class="mw-heading mw-heading3"><h3 id="Single_rail_and_double_rail">Single rail and double rail</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=10" title="Edit section: Single rail and double rail"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In non-electrified areas, insulated blockjoints come in pairs, one on each rail. </p><p>In electrified areas, a workaround is needed to allow the traction current, of the order of thousands of amperes, to return to the substation. This may be achieved by having no insulated block joints in one of the rails, called the return rail. </p><p>If both rails are needed to carry the heavy traction return current, then insulated blockjoints are provided in both rails, and impedance bonds are provided to carry the traction current around the insulated joints. Impedance bonds are essentially centre-tapped coils, which offer low impedance to traction current at say 50 Hz, while offering high impedance to signalling current at say 1.7 kHz. </p> <div class="mw-heading mw-heading2"><h2 id="Failure_modes_and_prevention">Failure modes and prevention</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=11" title="Edit section: Failure modes and prevention"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Wheels_and_brakes">Wheels and brakes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=12" title="Edit section: Wheels and brakes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Railway wheels are made from steel and provide a good short circuit from rail to rail (<i>shunt resistance</i>). </p><p>Longer trains with more wheels have better conductivity. Short trains, light railmotors or single engines can be a problem. In New Zealand there were problems with light <a href="/wiki/NZR_RM_class" title="NZR RM class">Rm class</a> railmotors not always being detected; see <a href="/wiki/Railway_signalling_in_New_Zealand#Signalling_equipment_problems_and_failures" title="Railway signalling in New Zealand">Railway signalling in New Zealand</a>. Trains with a single <a href="/wiki/Budd_Company" title="Budd Company">Budd</a> railmotor, which are also lightweight, and with discbrakes, had some problems when they stopped, and had to make a double stop to ensure good contact with the rails.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (September 2009)">citation needed</span></a></i>]</sup> </p><p>Cast iron brake shoes tend to clean the wheels of non-conductive debris (such as leaves and sand-based traction compounds), while <a href="/wiki/Disc_brake" title="Disc brake">disc brakes</a> do not. As a result, some disc-braked vehicles have "scrubber pads" cleaning the wheels to aid in proper track circuit operation.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (September 2009)">citation needed</span></a></i>]</sup> </p> <div class="mw-heading mw-heading3"><h3 id="Relays">Relays</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=13" title="Edit section: Relays"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Track circuit <a href="/wiki/Relay#Railway_signalling" title="Relay">relays</a>, referred to by signal maintainers as "vital relays," are specially designed to reduce the chance of <a href="/wiki/Wrong-side_failure" title="Wrong-side failure">wrong-side failures</a>. They may, for example, have carbon-silver contacts to reduce the likelihood of the wrong contacts welding shut after power surges and lightning strikes. </p> <div class="mw-heading mw-heading3"><h3 id="Circuit_failures">Circuit failures</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=14" title="Edit section: Circuit failures"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The circuit is designed so the vast majority of failures will cause a "track occupied" indication (known as a right-side failure). For example: </p> <ul><li>A broken rail or wire will break the circuit between the power supply and the relay, de-energizing the relay. See exception below.</li> <li>A failure in the power supply will de-energize the relay.</li> <li>A short across the rails or between adjacent track sections will de-energize the relay.</li></ul> <p>On the other hand, failure modes which prevent the circuit from detecting trains (known as a wrong-side failure) are possible. Examples include: </p> <ul><li>Mechanical failure of the relay, causing the relay to be stuck in the "track clear" position even when the track is occupied. <ul><li>One perspex case warped in the heat, and touched the relay contacts, holding them up.</li> <li>Another Q-series "miniature" relay saw a metal washer slip off and jam the relay contacts up; the half-washers had to be replaced by full-circle washers.</li></ul></li> <li>Conditions which partially or completely insulate the wheels from the rail, such as rust, sand, or dry leaves on the rails. This is also known as "poor shunting" ("failure to shunt" in North America and Australia). Sanding gear which operates on all wheels of an engine traveling light can temporarily insulate it from the rails until the sanding ceases and the locomotive has moved further down the track.</li> <li>Where multiple parallel paths exist for traction return purposes broken rail detection will be lost for the rail that is used for the traction return. If more than one break occurs in that rail a false clear can occur when the train is between the breaks.</li> <li>Conditions in the <a href="/wiki/Trackbed" class="mw-redirect" title="Trackbed">trackbed (roadbed)</a> which create stray electrical signals, such as muddy ballast (which can generate a "battery effect") or <a href="/wiki/Faraday%27s_law_of_induction#Parasitic_induction_and_waste_heating" title="Faraday's law of induction">parasitic electrical currents</a> from nearby power transmission lines.</li> <li><a href="/wiki/Parasitic_oscillation" title="Parasitic oscillation">Parasitic oscillations</a> in the equipment that controls the track circuits.<sup id="cite_ref-metro_4-0" class="reference"><a href="#cite_note-metro-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></li> <li>Equipment which is not heavy enough to make good electrical contact (shunt failure) or whose wheels must be electrically insulated.</li> <li>A rail break between the insulated rail joint and the track circuit feed wiring would not be detected.</li></ul> <p>Failure modes that result in an incorrect "track clear" signal (known usually in North America as a "false clear") may allow a train to enter an occupied block, creating the risk of a collision. Wheel scale and short trains may also be a problem. They may also cause the warning systems at a grade crossing to fail to activate. This is why in UK practice, a <a href="/wiki/Treadle_(railway)" title="Treadle (railway)">treadle</a> is also used in crossing circuitry. </p><p>Different means are used to respond to these types of failures. For example, the relays are designed to a very high level of reliability. In areas with electrical problems, different types of track circuits may be used which are less susceptible to interference. Speeds may be restricted when and where fallen leaves are an issue. Traffic may be embargoed to let equipment pass which does not reliably shunt the rails. </p><p>Sabotage is possible. In the <a href="/wiki/1995_Palo_Verde_derailment" class="mw-redirect" title="1995 Palo Verde derailment">1995 Palo Verde derailment</a>, saboteurs electrically connected sections of rail which they had displaced to conceal the breaks in the track they had made. The track circuit therefore did not detect the breaks, and the engine driver was not given a "Stop" indication. Another form of sabotage, not intended to cause a train crash but merely to make trains stop and slow down unnecessarily in an effort to sabotage an economy or potential injuries, is to tie a wire between the 2 rails, causing a false obstruction signal.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Railhead_contamination_and_rust">Railhead contamination and rust</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=15" title="Edit section: Railhead contamination and rust"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The track circuit relies upon an adequate electrical contact between the rail and the wheel; contamination can insulate the one from the other. A common problem is fallen leaves, though there have been cases where crushed insects have also caused detection failures.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>A more persistent problem is rust. Usually the railhead is kept clean of rust by the regular passage of trains' wheels. Lines which are not used regularly can become so rusty as to prevent vehicles being detected. Seldom-used points and crossovers and the extremities of terminal platform lines are also prone to rusting. Measures to overcome this include: </p> <ul><li><i>Depression bars</i> or <i>treadles</i> to detect vehicles; these are mechanical;</li> <li><i><a href="/wiki/Stainless_steel" title="Stainless steel">Stainless steel</a> strips</i> (often zig zag in shape) welded on the railheads; stainless steel does not rust;</li> <li><i>High-voltage impulse</i> track circuits;</li> <li><i>Track circuit assistor (TCA)</i> - a train-mounted system that breaks down the resistance of the rust layer;</li> <li><i><a href="/wiki/Axle_counters" class="mw-redirect" title="Axle counters">Axle counters</a></i> over the affected section</li> <li><i>Tunnel sticks</i> whereby a track circuit cannot pick up unless a train is detected in the next track circuit.</li></ul> <div class="mw-heading mw-heading3"><h3 id="Scale">Scale</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=16" title="Edit section: Scale"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Insulated blockjoints can be bridged by wheel scale in some circumstances causing one or two track circuits to fail. This problem may be reduced by having a pair of blockjoints in series about 4 m apart. The short 4 m section would not itself be track circuited.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Immunization">Immunization</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=17" title="Edit section: Immunization"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Electric locomotives must avoid generating noise in the frequencies that track circuits use. The <a href="/wiki/SNCB_Class_13" class="mw-redirect" title="SNCB Class 13">SNCB Class 13</a> had such problems. </p> <div class="mw-heading mw-heading3"><h3 id="Transitory_problems">Transitory problems</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=18" title="Edit section: Transitory problems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A short, lightweight and fast train passing over an insulated blockjoint may disappear from the departing track circuit before it appears in the arriving track circuit, allowing false clear signals to be given. This problem can be overcome by introducing a time delay of say 1–2 seconds into the departing track circuit. Electronic track circuits such as the CSEE can easily incorporate such a time delay. </p> <div class="mw-heading mw-heading2"><h2 id="Siding_turnout">Siding turnout</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=19" title="Edit section: Siding turnout"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>It is sometimes convenient to wire the detectors of a set of points through the track circuit over those points. This can be done in one of two ways: </p> <ul><li>A contact of the points detector can shunt the track circuit when the points are reverse, putting the signals to red, however this is not failsafe.</li> <li>The track circuit can be split with extra blockjoints and the detectors in the points complete the track circuit when the points are normal and the signal is entitled to receive a green light. This is partially fail-safe.</li> <li>A second relay can be installed on the turnout, with its contacts wired in series with the main relay. This is fail-safe but expensive.<sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Accuracy_dispute#Disputed_statement" title="Wikipedia:Accuracy dispute"><span title="See talk section (September 2015)">dubious</span></a> – <a href="/wiki/Talk:Track_circuit#Siding_Turnout" title="Talk:Track circuit">discuss</a></i>]</sup></li></ul> <div class="mw-heading mw-heading2"><h2 id="Track-circuit_operating_clips">Track-circuit operating clips</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=20" title="Edit section: Track-circuit operating clips"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A simple piece of safety equipment which is carried by all heavy rail trains in Britain is a <i>track-circuit operating clip (TCOC)</i>.<sup id="cite_ref-tcoc_9-0" class="reference"><a href="#cite_note-tcoc-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> This is a length of wire connecting two metal spring clips that clip onto a rail. In the event of accident or obstruction a clip applied to both rails will indicate that that line is occupied, putting the signal for that section to danger. </p><p><i>Emergency protection</i> procedure<sup id="cite_ref-tcoc_9-1" class="reference"><a href="#cite_note-tcoc-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> in the UK requires TCOCs to be placed on all affected running lines if contact cannot be made immediately with the signaller following an accident where adjacent lines are blocked. </p><p>TCOCs are ineffective where train detection is not by means of track circuits, such as <a href="/wiki/Axle_counters" class="mw-redirect" title="Axle counters">axle counters</a> or <a href="/wiki/Treadle_(railway)" title="Treadle (railway)">treadles</a>. </p> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=21" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The first use of track circuiting was by <a href="/wiki/William_Robert_Sykes" title="William Robert Sykes">William Robert Sykes</a> on a short stretch of track of the <a href="/wiki/London_Chatham_and_Dover_Railway" class="mw-redirect" title="London Chatham and Dover Railway">London Chatham and Dover Railway</a> at Brixton in 1864.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> The failsafe track circuit was invented in 1872 by <a href="/wiki/William_Robinson_(inventor)" title="William Robinson (inventor)">William Robinson</a>, an American electrical and mechanical engineer. His introduction of a trustworthy method of block occupancy detection was key to the development of the automatic signalling systems now in nearly universal use.<sup id="cite_ref-ARA_11-0" class="reference"><a href="#cite_note-ARA-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 3ff">: 3ff </span></sup> </p><p>The first railway signals were manually operated by <a href="/wiki/Signalman_(rail)" class="mw-redirect" title="Signalman (rail)">signal tenders</a> or station agents. When to change the signal aspect was often left to the judgement of the operator. Human error or inattentiveness occasionally resulted in improper signalling and train collisions. </p><p>The introduction of the <a href="/wiki/Electrical_telegraph" title="Electrical telegraph">telegraph</a> during the mid-nineteenth century showed that information could be electrically conveyed over considerable distance, spurring the investigation into methods of electrically controlling railway signals. Although several systems were developed prior to Robinson's, none could automatically respond to train movements. </p><p>Robinson first demonstrated a fully automatic railway signalling system in model form in 1870. A full-sized version was subsequently installed on the <a href="/wiki/Philadelphia_and_Erie_Railroad" title="Philadelphia and Erie Railroad">Philadelphia and Erie Railroad</a> at <a href="/wiki/Ludlow,_Pennsylvania" title="Ludlow, Pennsylvania">Ludlow, Pennsylvania</a> (aka Kinzua, PA), where it proved to be practical. His design consisted of electrically operated discs located atop small trackside signal huts, and was based on an open track circuit. When no train was within the block no power was applied to the signal, indicating a clear track.<sup id="cite_ref-ARA_11-1" class="reference"><a href="#cite_note-ARA-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 4">: 4 </span></sup> </p><p>An inherent weakness of this arrangement was that it could fail in an unsafe state. For example, a broken wire in the track circuit would falsely indicate that no train was in the block, even if one was. Recognizing this, Robinson devised the closed loop track circuit described above, and in 1872, installed it in place of the previous circuit. The result was a fully automatic, failsafe signalling system that was the prototype for subsequent development.<sup id="cite_ref-ARA_11-2" class="reference"><a href="#cite_note-ARA-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 6–9">: 6–9 </span></sup> </p><p>Although a pioneer in the use of signals controlling trains, the UK was slow to adopt Robinson's design. At the time, many carriages on UK railways had wooden axles and/or wheels with wooden hubs, making them incompatible with track circuits. </p> <div class="mw-heading mw-heading2"><h2 id="Accidents">Accidents</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=22" title="Edit section: Accidents"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Caused_by_lack_of_track_circuits">Caused by lack of track circuits</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=23" title="Edit section: Caused by lack of track circuits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Numerous accidents would have been prevented by the provision of track circuits, including: </p> <ul><li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_Kingdom" title="United Kingdom"><img alt="United Kingdom" src="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/23px-Flag_of_the_United_Kingdom.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/35px-Flag_of_the_United_Kingdom.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/46px-Flag_of_the_United_Kingdom.svg.png 2x" data-file-width="1200" data-file-height="600" /></a></span></span> <a href="/wiki/Norton_Fitzwarren_rail_crash_(1890)" class="mw-redirect" title="Norton Fitzwarren rail crash (1890)">Norton Fitzwarren rail crash (1890)</a></li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_Kingdom" title="United Kingdom"><img alt="United Kingdom" src="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/23px-Flag_of_the_United_Kingdom.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/35px-Flag_of_the_United_Kingdom.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/46px-Flag_of_the_United_Kingdom.svg.png 2x" data-file-width="1200" data-file-height="600" /></a></span></span> <a href="/wiki/Hawes_Junction_rail_crash" title="Hawes Junction rail crash">Hawes Junction rail crash</a> (1910)</li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_Kingdom" title="United Kingdom"><img alt="United Kingdom" src="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/23px-Flag_of_the_United_Kingdom.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/35px-Flag_of_the_United_Kingdom.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/46px-Flag_of_the_United_Kingdom.svg.png 2x" data-file-width="1200" data-file-height="600" /></a></span></span> <a href="/wiki/Quintinshill_rail_crash" class="mw-redirect" title="Quintinshill rail crash">Quintinshill rail crash</a> (1915)</li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/Australia" title="Australia"><img alt="Australia" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/23px-Flag_of_Australia_%28converted%29.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/35px-Flag_of_Australia_%28converted%29.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/46px-Flag_of_Australia_%28converted%29.svg.png 2x" data-file-width="1280" data-file-height="640" /></a></span></span> <a href="/wiki/Geurie_crossing_loop_collision" title="Geurie crossing loop collision">Geurie crossing loop collision</a> (1963)</li></ul> <div class="mw-heading mw-heading3"><h3 id="Caused_by_track_circuit_failure">Caused by track circuit failure</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=24" title="Edit section: Caused by track circuit failure"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Much rarer are accidents caused when the track circuits themselves fail. For example: </p> <ul><li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/Australia" title="Australia"><img alt="Australia" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/23px-Flag_of_Australia_%28converted%29.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/35px-Flag_of_Australia_%28converted%29.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/88/Flag_of_Australia_%28converted%29.svg/46px-Flag_of_Australia_%28converted%29.svg.png 2x" data-file-width="1280" data-file-height="640" /></a></span></span> <a href="/wiki/Cowan_rail_disaster" class="mw-redirect" title="Cowan rail disaster">Cowan rail disaster</a>, which occurred when sand on the rails insulated the wheels from the rails, causing a failure to shunt that allowed a trailing <a href="/wiki/Railway_signal" title="Railway signal">block signal</a> to improperly display a clear aspect, resulting in a rear-end collision.</li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/Czech_Republic" title="Czech Republic"><img alt="Czech Republic" src="//upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Flag_of_the_Czech_Republic.svg/23px-Flag_of_the_Czech_Republic.svg.png" decoding="async" width="23" height="15" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Flag_of_the_Czech_Republic.svg/35px-Flag_of_the_Czech_Republic.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Flag_of_the_Czech_Republic.svg/45px-Flag_of_the_Czech_Republic.svg.png 2x" data-file-width="900" data-file-height="600" /></a></span></span> <a href="/w/index.php?title=Moravany_railway_crash&action=edit&redlink=1" class="new" title="Moravany railway crash (page does not exist)">Moravany railway crash</a>, occurred in <a href="/wiki/Moravany_(Pardubice_District)" title="Moravany (Pardubice District)">Moravany</a> railway station. Broken sand dispenser caused a layer of sand being created on the rail, making it lose the shunt. The station equipment interpreted this as the track is free and allowed another train in to proceed into the station, which then crashed into the previous train from behind.<sup id="cite_ref-moravany_12-0" class="reference"><a href="#cite_note-moravany-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup></li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_States" title="United States"><img alt="United States" src="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/23px-Flag_of_the_United_States.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/35px-Flag_of_the_United_States.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/46px-Flag_of_the_United_States.svg.png 2x" data-file-width="1235" data-file-height="650" /></a></span></span> <a href="/wiki/June_22,_2009_Washington_Metro_train_collision" class="mw-redirect" title="June 22, 2009 Washington Metro train collision">June 22, 2009 Washington Metro train collision</a>, which occurred when a <a href="/wiki/Parasitic_oscillation" title="Parasitic oscillation">parasitic oscillation</a> developed in a track circuit control module.<sup id="cite_ref-metro_4-1" class="reference"><a href="#cite_note-metro-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></li></ul> <div class="mw-heading mw-heading3"><h3 id="Broken_rails">Broken rails</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=25" title="Edit section: Broken rails"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because Track circuits operate by passing a current through one or both of the tracks, they can sometimes detect if a rail has broken completely. However, if the break is only partial or is at a turnout (set of points) detection may not be possible. </p> <ul><li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_Kingdom" title="United Kingdom"><img alt="United Kingdom" src="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/23px-Flag_of_the_United_Kingdom.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/35px-Flag_of_the_United_Kingdom.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/ae/Flag_of_the_United_Kingdom.svg/46px-Flag_of_the_United_Kingdom.svg.png 2x" data-file-width="1200" data-file-height="600" /></a></span></span> <a href="/wiki/Hither_Green_rail_crash" title="Hither Green rail crash">Hither Green rail crash</a> (1967) - derailment due to top of rail having broken off</li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_States" title="United States"><img alt="United States" src="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/23px-Flag_of_the_United_States.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/35px-Flag_of_the_United_States.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/46px-Flag_of_the_United_States.svg.png 2x" data-file-width="1235" data-file-height="650" /></a></span></span> <a href="/wiki/Weyauwega_derailment" class="mw-redirect" title="Weyauwega derailment">Weyauwega derailment</a> (1996) - undetected broken rail in turnout.</li> <li><span class="flagicon"><span class="mw-image-border" typeof="mw:File"><a href="/wiki/United_States" title="United States"><img alt="United States" src="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/23px-Flag_of_the_United_States.svg.png" decoding="async" width="23" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/35px-Flag_of_the_United_States.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/a/a4/Flag_of_the_United_States.svg/46px-Flag_of_the_United_States.svg.png 2x" data-file-width="1235" data-file-height="650" /></a></span></span> <a href="/wiki/Big_Bayou_Canot_rail_accident" title="Big Bayou Canot rail accident">Big Bayou Canot rail accident</a> (1993) - undetected <i>unbroken</i> but badly twisted continuous welded rail on a bridge that still indicated a clear condition to the signal.</li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=26" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Application_of_railway_signals" title="Application of railway signals">Application of railway signals</a></li> <li><a href="/wiki/Track_circuit_interrupter" title="Track circuit interrupter">Track circuit interrupter</a></li> <li><a href="/wiki/Wrong-side_failure" title="Wrong-side failure">Wrong-side failure</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Track_circuit&action=edit&section=27" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239549316">.mw-parser-output .refbegin{margin-bottom:0.5em}.mw-parser-output .refbegin-hanging-indents>ul{margin-left:0}.mw-parser-output .refbegin-hanging-indents>ul>li{margin-left:0;padding-left:3.2em;text-indent:-3.2em}.mw-parser-output .refbegin-hanging-indents ul,.mw-parser-output .refbegin-hanging-indents ul li{list-style:none}@media(max-width:720px){.mw-parser-output .refbegin-hanging-indents>ul>li{padding-left:1.6em;text-indent:-1.6em}}.mw-parser-output .refbegin-columns{margin-top:0.3em}.mw-parser-output .refbegin-columns ul{margin-top:0}.mw-parser-output .refbegin-columns li{page-break-inside:avoid;break-inside:avoid-column}@media screen{.mw-parser-output .refbegin{font-size:90%}}</style><div class="refbegin" style=""> </div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://extranet.artc.com.au/docs/eng/signal/procedures/examination/SES06.pdf">"CSEE UM71 AF Jointless Track Circuits – Set-up, Test and Certification SES 06"</a> <span class="cs1-format">(PDF)</span>. Australian Rail Track Corporation Ltd<span class="reference-accessdate">. Retrieved <span class="nowrap">13 April</span> 2012</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=CSEE+UM71+AF+Jointless+Track+Circuits+%E2%80%93+Set-up%2C+Test+and+Certification+SES+06&rft.pub=Australian+Rail+Track+Corporation+Ltd&rft_id=http%3A%2F%2Fextranet.artc.com.au%2Fdocs%2Feng%2Fsignal%2Fprocedures%2Fexamination%2FSES06.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://extranet.artc.com.au/docs/eng/signal/procedures/maintenance/ESM-07-03.pdf">"Microtrax Coded Track Circuits ESM-07-03"</a> <span class="cs1-format">(PDF)</span>. Australian Rail Track Corporation Limited<span class="reference-accessdate">. Retrieved <span class="nowrap">13 April</span> 2012</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Microtrax+Coded+Track+Circuits+ESM-07-03&rft.pub=Australian+Rail+Track+Corporation+Limited&rft_id=http%3A%2F%2Fextranet.artc.com.au%2Fdocs%2Feng%2Fsignal%2Fprocedures%2Fmaintenance%2FESM-07-03.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCallender" class="citation web cs1">Callender, Earl. <a rel="nofollow" class="external text" href="http://www.irse.org.au/index.php/en/component/docman/doc_download/284-an-application-of-microtrax?Itemid=71">"An Application of Microtrax for the National Rail Corporation on the SRA-NSW North Coast Line"</a>. Union Switch & Signal<span class="reference-accessdate">. Retrieved <span class="nowrap">13 April</span> 2012</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=An+Application+of+Microtrax+for+the+National+Rail+Corporation+on+the+SRA-NSW+North+Coast+Line&rft.pub=Union+Switch+%26+Signal&rft.aulast=Callender&rft.aufirst=Earl&rft_id=http%3A%2F%2Fwww.irse.org.au%2Findex.php%2Fen%2Fcomponent%2Fdocman%2Fdoc_download%2F284-an-application-of-microtrax%3FItemid%3D71&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-metro-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-metro_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-metro_4-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">National Transportation Safety Board (NTSB), Washington, D.C. (2009-09-22). <a rel="nofollow" class="external text" href="http://www.wmata.com/about_metro/WMATASafetyRecLtr.pdf">"Safety Recommendations R-09-15 and R-09-16."</a> Letter from Deborah A.P. Hersman, Chairman, NTSB, to John B. Catoe, Jr., General Manager, Washington Metropolitan Area Transit Authority.</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text">Ezra Levant, The Source, Sun News Network, "Summer Of Terror" <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20131204165727/http://www.sunnewsnetwork.ca/sunnews/straighttalk/archives/2013/07/20130709-072337.html">"Sun News : Summer of terror?"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.sunnewsnetwork.ca/sunnews/straighttalk/archives/2013/07/20130709-072337.html">the original</a> on 2013-12-04<span class="reference-accessdate">. Retrieved <span class="nowrap">2013-07-12</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Sun+News+%3A+Summer+of+terror%3F&rft_id=http%3A%2F%2Fwww.sunnewsnetwork.ca%2Fsunnews%2Fstraighttalk%2Farchives%2F2013%2F07%2F20130709-072337.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text">Anarchist News, Southern Ontario: Solidarity CN Rail Signal Sabotage Tue, 01/15/2013 - 12:53 -- Anonymous (not verified)<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20130912014640/http://anarchistnews.org/content/southern-ontario-solidarity-cn-rail-signal-sabotage">"Southern Ontario: Solidarity CN Rail Signal Sabotage | anarchistnews dot org"</a>. Archived from <a rel="nofollow" class="external text" href="http://anarchistnews.org/content/southern-ontario-solidarity-cn-rail-signal-sabotage">the original</a> on 2013-09-12<span class="reference-accessdate">. Retrieved <span class="nowrap">2013-07-12</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Southern+Ontario%3A+Solidarity+CN+Rail+Signal+Sabotage+%26%23124%3B+anarchistnews+dot+org&rft_id=http%3A%2F%2Fanarchistnews.org%2Fcontent%2Fsouthern-ontario-solidarity-cn-rail-signal-sabotage&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJess2009" class="citation news cs1">Jess, Allison (2009-05-11). <a rel="nofollow" class="external text" href="http://www.abc.net.au/local/stories/2009/05/11/2566690.htm">"Millipede mayhem"</a>. <i>ABC Goulburn Valley</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2012-10-22</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=ABC+Goulburn+Valley&rft.atitle=Millipede+mayhem&rft.date=2009-05-11&rft.aulast=Jess&rft.aufirst=Allison&rft_id=http%3A%2F%2Fwww.abc.net.au%2Flocal%2Fstories%2F2009%2F05%2F11%2F2566690.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text">Rail Corporation New South Wales, Haymarket NSW Australia (2012). <a rel="nofollow" class="external text" href="http://engineering.railcorp.nsw.gov.au/Disciplines/Civil/ESC_220.pdf">"ESC 220: Rail and Rail Joints."</a>. Engineering Standard. Version 4.7.</span> </li> <li id="cite_note-tcoc-9"><span class="mw-cite-backlink">^ <a href="#cite_ref-tcoc_9-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-tcoc_9-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRSSB2012" class="citation book cs1 cs1-prop-long-vol"><a href="/wiki/Rail_Safety_and_Standards_Board" title="Rail Safety and Standards Board">RSSB</a> (2012-12-02). <i>Railway Rule Book</i>. Vol. Module M: Dealing with a train accident or train evacuation, Emergency Protection. p. Section 2. GERT8000.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Railway+Rule+Book&rft.pages=Section+2&rft.date=2012-12-02&rft.au=RSSB&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMarshall1978" class="citation book cs1">Marshall, John (1978). <i>A biographical dictionary of railway engineers</i>. Newton Abbot, Oxford: David & Charles. p. 162. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-7153-7489-3" title="Special:BookSources/0-7153-7489-3"><bdi>0-7153-7489-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+biographical+dictionary+of+railway+engineers&rft.place=Newton+Abbot%2C+Oxford&rft.pages=162&rft.pub=David+%26+Charles&rft.date=1978&rft.isbn=0-7153-7489-3&rft.aulast=Marshall&rft.aufirst=John&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-ARA-11"><span class="mw-cite-backlink">^ <a href="#cite_ref-ARA_11-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-ARA_11-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-ARA_11-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAmerican_Railway_Association_(ARA)1922" class="citation book cs1">American Railway Association (ARA) (1922). <a rel="nofollow" class="external text" href="https://archive.org/details/inventionoftrack00newyrich"><i>The Invention of the Track Circuit</i></a>. New York: ARA.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Invention+of+the+Track+Circuit&rft.place=New+York&rft.pub=ARA&rft.date=1922&rft.au=American+Railway+Association+%28ARA%29&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Finventionoftrack00newyrich&rfr_id=info%3Asid%2Fen.wikipedia.org%3ATrack+circuit" class="Z3988"></span></span> </li> <li id="cite_note-moravany-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-moravany_12-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.dicr.cz/files/uploads/Zpravy/MU/MU_Moravany.pdf">"Srážka lokomotivního vlaku Lv 72461 s osobním vlakem Os 5011</a></span> </li> </ol></div></div> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output 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href="/wiki/Template:Railway_signalling" title="Template:Railway signalling"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Railway_signalling" title="Template talk:Railway signalling"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Railway_signalling" title="Special:EditPage/Template:Railway signalling"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Railway_signalling" style="font-size:114%;margin:0 4em"><a href="/wiki/Railway_signalling" title="Railway signalling">Railway signalling</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Signalling_block_system" title="Signalling block system">Block systems</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Absolute_block_signalling" title="Absolute block signalling">Absolute block signalling</a></li> <li><a href="/wiki/Automatic_block_signaling" title="Automatic block signaling">Automatic block signaling</a></li> <li><a href="/wiki/Centralized_traffic_control" title="Centralized traffic control">Centralized traffic control</a></li> <li><a href="/wiki/Communications-based_train_control" title="Communications-based train control">Communications-based train control</a></li> <li><a href="/wiki/Direct_traffic_control" title="Direct traffic control">Direct traffic control</a></li> <li><a href="/wiki/European_Train_Control_System" title="European Train Control System">European Train Control System</a></li> <li><a href="/wiki/Moving_block" title="Moving block">Moving block</a></li> <li><a href="/wiki/Radio_Electronic_Token_Block" title="Radio Electronic Token Block">Radio Electronic Token Block</a></li> <li><a href="/wiki/Token_(railway_signalling)" title="Token (railway signalling)">Token</a></li> <li><a href="/wiki/Track_Warrant_Control" title="Track Warrant Control">Track Warrant Control</a></li> <li><a href="/wiki/Train_order_operation" title="Train order operation">Train order operation</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Signalling_control" title="Signalling control">Signalling control</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Block_post" title="Block post">Block post</a></li> <li><a href="/wiki/Integrated_Electronic_Control_Centre" title="Integrated Electronic Control Centre">Integrated Electronic Control Centre</a></li> <li><a href="/wiki/Interlocking" title="Interlocking">Interlocking</a></li> <li><a href="/wiki/Lever_frame" title="Lever frame">Lever frame</a></li> <li><a href="/wiki/Rail_operating_centre" title="Rail operating centre">Rail operating centre</a></li> <li><a href="/wiki/Solid_State_Interlocking" title="Solid State Interlocking">Solid State Interlocking</a></li> <li><a href="/wiki/Westlock_Interlocking" title="Westlock Interlocking">Westlock Interlocking</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Railway_signal" title="Railway signal">Signals</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Application_of_railway_signals" title="Application of railway signals">Application of railway signals</a></li> <li><a href="/wiki/Cab_signalling" title="Cab signalling">Cab signalling</a></li> <li><a href="/wiki/North_American_railroad_signals" title="North American railroad signals">North American railroad signals</a></li> <li><a href="/wiki/Railway_semaphore_signal" title="Railway semaphore signal">Railway semaphore signal</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Train detection</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Axle_counter" title="Axle counter">Axle counter</a></li> <li><a class="mw-selflink selflink">Track circuit</a></li> <li><a href="/wiki/Track_circuit_interrupter" title="Track circuit interrupter">Track circuit interrupter</a></li> <li><a href="/wiki/Treadle_(railway)" title="Treadle (railway)">Treadle</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Train_protection_system" title="Train protection system">Train protection</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Advanced_Civil_Speed_Enforcement_System" title="Advanced Civil Speed Enforcement System">Advanced Civil Speed Enforcement System</a></li> <li><a href="/wiki/ALSN" title="ALSN">ALSN</a></li> <li><a href="/wiki/Anuncio_de_Se%C3%B1ales_y_Frenado_Autom%C3%A1tico" title="Anuncio de Señales y Frenado Automático">ASFA</a></li> <li><a href="/wiki/ATACS" title="ATACS">ATACS</a></li> <li><a href="/wiki/Automatic_train_control" title="Automatic train control">Automatic train control</a></li> <li><a href="/wiki/Automatic_train_operation" title="Automatic train operation">Automatic train operation</a></li> <li><a href="/wiki/Automatic_train_protection" title="Automatic train protection">Automatic train protection</a></li> <li><a href="/wiki/Automatic_Train_Protection_(United_Kingdom)" title="Automatic Train Protection (United Kingdom)">Automatic Train Protection (United Kingdom)</a></li> <li><a href="/wiki/Automatic_train_stop" title="Automatic train stop">Automatic train stop</a></li> <li><a href="/wiki/Automatic_Warning_System" title="Automatic Warning System">Automatic Warning System</a></li> <li><a href="/wiki/Automatische_treinbe%C3%AFnvloeding" title="Automatische treinbeïnvloeding">Automatische treinbeïnvloeding</a></li> <li><a href="/wiki/Balise" title="Balise">Balise</a></li> <li><a href="/wiki/Catch_points" title="Catch points">Catch points</a></li> <li><a href="/wiki/Chinese_Train_Control_System" title="Chinese Train Control System">Chinese Train Control System</a></li> <li><a href="/wiki/Cityflo_650_CBTC" title="Cityflo 650 CBTC">Cityflo 650 CBTC</a></li> <li><a href="/wiki/Continuous_Automatic_Warning_System" title="Continuous Automatic Warning System">Continuous Automatic Warning System</a></li> <li><a href="/wiki/Contr%C3%B4le_de_vitesse_par_balises" title="Contrôle de vitesse par balises">Contrôle de vitesse par balises</a></li> <li><a href="/wiki/EBICAB" title="EBICAB">EBICAB</a></li> <li><a href="/wiki/Intermittent_inductive_automatic_train_stop" title="Intermittent inductive automatic train stop">IIATS</a></li> <li><a href="/wiki/Integra-Signum" title="Integra-Signum">Integra-Signum</a></li> <li><a href="/wiki/Interoperable_Communications_Based_Signaling" title="Interoperable Communications Based Signaling">Interoperable Communications Based Signaling</a></li> <li><a href="/wiki/Crocodile_(train_protection_system)" title="Crocodile (train protection system)">Crocodile</a></li> <li><a href="/wiki/Linienzugbeeinflussung" title="Linienzugbeeinflussung">Linienzugbeeinflussung</a></li> <li><a href="/wiki/Positive_train_control" title="Positive train control">Positive Train Control</a></li> <li><a href="/wiki/Pulse_code_cab_signaling" title="Pulse code cab signaling">Pulse code cab signaling</a></li> <li><a href="/wiki/Punktf%C3%B6rmige_Zugbeeinflussung" title="Punktförmige Zugbeeinflussung">Punktförmige Zugbeeinflussung</a></li> <li><a href="/wiki/RS4_Codici" title="RS4 Codici">RS4 Codici</a></li> <li><a href="/wiki/SelTrac" title="SelTrac">SelTrac</a></li> <li><a href="/wiki/Sistema_Controllo_Marcia_Treno" title="Sistema Controllo Marcia Treno">Sistema Controllo Marcia Treno</a></li> <li><a href="/wiki/Syst%C3%A8me_d%27aide_%C3%A0_la_conduite,_%C3%A0_l%27exploitation_et_%C3%A0_la_maintenance" class="mw-redirect" title="Système d'aide à la conduite, à l'exploitation et à la maintenance">SACEM</a></li> <li><a href="/wiki/Railway_slide_fence" title="Railway slide fence">Slide fence</a></li> <li><a href="/wiki/Train_automatic_stopping_controller" title="Train automatic stopping controller">Train automatic stopping controller</a></li> <li><a href="/wiki/Train_Protection_%26_Warning_System" title="Train Protection & Warning System">Train Protection & Warning System</a></li> <li><a href="/wiki/Train_stop" title="Train stop">Train stop</a></li> <li><a href="/wiki/Trainguard_MT" title="Trainguard MT">Trainguard MT</a></li> <li><a href="/wiki/Transmission_balise-locomotive" title="Transmission balise-locomotive">Transmission balise-locomotive</a></li> <li><a href="/wiki/Transmission_Voie-Machine" title="Transmission Voie-Machine">Transmission Voie-Machine</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Crossing signals</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Level_crossing_signals" title="Level crossing signals">Level crossing signals</a></li> <li><a href="/wiki/Crossbuck" title="Crossbuck">Crossbuck</a></li> <li><a href="/wiki/Wigwag_(railroad)" title="Wigwag (railroad)">Wigwag</a></li> <li><a href="/wiki/E-signal" title="E-signal">E-signal</a></li> <li><a href="/wiki/Wayside_horn" title="Wayside horn">Wayside horn</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Manufacturers</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Adtranz" title="Adtranz">Adtranz</a></li> <li><a href="/wiki/Alstom" title="Alstom">Alstom</a></li> <li><a href="/wiki/A%C5%BDD_Praha" title="AŽD Praha">AŽD Praha</a></li> <li><a href="/wiki/Federal_Signal_Company" title="Federal Signal Company">Federal</a></li> <li><a href="/wiki/General_Electric" title="General Electric">General Electric</a></li> <li><a href="/wiki/General_Railway_Signal" title="General Railway Signal">GRS</a></li> <li><a href="/wiki/Griswold_Signal_Company" title="Griswold Signal Company">Griswold</a></li> <li><a href="/wiki/Hall_Signal_Company" title="Hall Signal Company">Hall</a></li> <li><a href="/wiki/Hitachi_Rail_STS" title="Hitachi Rail STS">Hitachi</a></li> <li><a href="/wiki/Magnetic_Signal_Company" title="Magnetic Signal Company">Magnetic</a></li> <li><a href="/wiki/Progress_Rail" title="Progress Rail">Progress Rail</a></li> <li><a href="/wiki/Safetran" title="Safetran">Safetran</a></li> <li><a href="/wiki/John_Saxby" title="John Saxby">Saxby</a></li> <li><a href="/wiki/Siemens_Mobility" title="Siemens Mobility">Siemens</a></li> <li><a href="/wiki/Smith_and_Yardley" title="Smith and Yardley">Smith and Yardley</a></li> <li><a href="/wiki/Thales_Rail_Signalling_Solutions" title="Thales Rail Signalling Solutions">Thales</a></li> <li><a href="/wiki/Union_Switch_%26_Signal" title="Union Switch & Signal">Union Switch</a></li> <li><a href="/wiki/Westinghouse_Brake_and_Signal_Company" title="Westinghouse Brake and Signal Company">Westinghouse Brake & Signal</a></li> <li><a href="/wiki/Westinghouse_Rail_Systems" title="Westinghouse Rail Systems">Westinghouse Rail Systems</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Organisations</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Association_of_American_Railroads" title="Association of American Railroads">AAR</a></li> <li><a href="/wiki/American_Railway_Engineering_and_Maintenance-of-Way_Association" title="American Railway Engineering and Maintenance-of-Way Association">AREMA</a></li> <li><a href="/wiki/European_Union_Agency_for_Railways" title="European Union Agency for Railways">ERA</a></li> <li><a href="/wiki/Federal_Railroad_Administration" title="Federal Railroad Administration">FRA</a></li> <li><a href="/wiki/His_Majesty%27s_Railway_Inspectorate" title="His Majesty's Railway Inspectorate">HMRI</a></li> <li><a href="/wiki/Institution_of_Railway_Signal_Engineers" title="Institution of Railway Signal Engineers">IRSE</a></li> <li><a href="/wiki/Transport_Canada" title="Transport Canada">Transport Canada</a></li> <li><a href="/wiki/International_Union_of_Railways" title="International Union of Railways">UIC</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">By country</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Australian_railway_signalling" title="Australian railway signalling">Australia</a></li> <li><a href="/wiki/Bavarian_railway_signals" title="Bavarian railway signals">Bavaria</a></li> <li><a href="/wiki/Belgian_railway_signalling" title="Belgian railway signalling">Belgium</a></li> <li><a href="/wiki/Canadian_Rail_Operating_Rules" title="Canadian Rail Operating Rules">Canada</a></li> <li><a href="/wiki/Chinese_railway_signalling" title="Chinese railway signalling">China</a></li> <li><a href="/wiki/Finnish_railway_signalling" title="Finnish railway signalling">Finland</a></li> <li><a href="/wiki/French_railway_signalling" title="French railway signalling">France</a></li> <li><a href="/wiki/Railway_signals_in_Germany" title="Railway signals in Germany">Germany</a></li> <li><a href="/wiki/Greek_railway_signalling" title="Greek railway signalling">Greece</a></li> <li><a href="/wiki/Italian_railway_signalling" title="Italian railway signalling">Italy</a></li> <li><a href="/wiki/Japanese_railway_signals" title="Japanese railway signals">Japan</a></li> <li><a href="/wiki/Dutch_railway_signalling" title="Dutch railway signalling">Netherlands</a></li> <li><a href="/wiki/Railway_signalling_in_New_Zealand" title="Railway signalling in New Zealand">New Zealand</a></li> <li><a href="/wiki/North_American_railroad_signaling" title="North American railroad signaling">North America</a></li> <li><a href="/wiki/Norwegian_railway_signaling" title="Norwegian railway signaling">Norway</a></li> <li><a href="/wiki/Polish_railway_signalling" title="Polish railway signalling">Poland</a></li> <li><a href="/wiki/Swedish_railway_signalling" title="Swedish railway signalling">Sweden</a></li> <li><a href="/wiki/Swiss_railway_signalling" title="Swiss railway signalling">Switzerland</a></li> <li><a href="/wiki/Thai_railway_signalling" title="Thai railway signalling">Thailand</a></li> <li><a href="/wiki/UK_railway_signalling" title="UK railway signalling">United Kingdom</a></li></ul> </div></td></tr></tbody></table></div>    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