# Computer-based interlocking

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{{Short description|Railway signal interlocking using computers}}
'''Computer-based interlocking''' (CBI) is [railway signal](/source/railway_signal) [interlocking](/source/interlocking) implemented with [computer](/source/computer)s and [semiconductors](/source/Semiconductor), rather than using older technologies such as [relays](/source/relays) or [mechanics](/source/mechanics). So it is a special subset (but most common implementation) of [Solid State Interlocking](/source/Solid_State_Interlocking) systems today. In some countries were hybrid constructions established with logic cores from computers and electromechanical interfaces to lineside systems.

== General ==

CBIs are mostly implemented in two parts:

* a section that implements the safety and failsafe requirements, and 
* a second section that implements "non-vital" controls and indications.

The [European Union](/source/European_Union) (EU) with its [European Railway Agency](/source/European_Union_Agency_for_Railways) (ERA) and [International Union of Railways](/source/International_Union_of_Railways) (UIC) have created an umbrella [European Railway Traffic Management Standard](/source/ERTMS) (ERTMS). Under this umbrella framework the interlockings are the interface with security relevance between the trains on the tracks and the higher levels of traffic management. The interface to rolling stock is defined by means of [European Traffic Control System](/source/European_Train_Control_System) (ETCS) as an collection of standards. The standardised communication interface [GSM-R](/source/GSM-R) has a global successor [FRMCS](/source/FRMCS). 

Because the interlockings are traditionally grounded in national infrastructure, they are not fully transparent and standardised. Despite the global companies implementing it, the local implementation is often proprietary closed. The EU is trying to open the framework of information by customers by means of [RailML](/source/RailML), thereby reducing nonstandard efforts and longterm costs.

== Brands ==

Different manufacturers have their own brands of CBI such as

* ''Alister'' from ''Funkwerk AG'' (Germany) [<nowiki/>[de](/source/%3Ade%3AFunkwerk_AG)]<ref>[Railway Gazette International](/source/Railway_Gazette_International) of July 2012, page 18</ref> 
* [EBILOCK](/source/EBILOCK) from [Bombardier Transportation](/source/Bombardier_Transportation), now [Alstom](/source/Alstom)<ref>{{Cite web |title=EBI Lock Computer-Based Interlocking Systems |url=https://www.railway-technology.com/products/ebi-lock-computer-based-interlocking-systems/ |access-date=2026-01-15 |website=Railway Technology |language=en-US}}</ref>
* [EI L90](/source/EI_L90) (also LockTrack L90 or ESTW L90) from [SEL](/source/Standard_Elektrik_Lorenz) -> [Alcatel](/source/Alcatel) -> [Thales](/source/Thales_Group) -> [Hitachi Rail STS](/source/Hitachi_Rail_STS)<ref>{{Cite web |date=2008-08-20 |title=LockTrac 6111 ESTW L90 - Electronic Interlocking System |url=https://scbist.com/scb/uploaded/72135_1371703727.pdf |url-status=live |access-date=2026-01-16}}</ref>
* [Microlok II](/source/Microlok_II) from Ansaldo STS -> Hitachi Rail STS<ref>{{Cite web |date=2010-08-13 |title=Microlok II Design |url=https://extranet.artc.com.au/docs/eng/signal/procedures/design/ESD-05-12.pdf |url-status=live |access-date=2026-01-15 |website= |publisher=[Australian Rail Track Corporation](/source/Australian_Rail_Track_Corporation) |format=PDF}}</ref>
* ''SIMIS-x'' (Siemens Mobility Interlocking System) from [Siemens Mobility](/source/Siemens_Mobility)<ref>{{Cite web |title=Interlocking System |url=https://www.mobility.siemens.com/global/en/portfolio/rail-infrastructure/mainline/interlocking-systems.html |access-date=2026-01-15 |website=Siemens Mobility Global |language=en}}</ref>
* ''Smartlock'' from [Alstom](/source/Alstom)<ref>{{Cite web |title=Interlocking 4.0: safe rail operations for increased capacity and reliability |url=https://www.alstom.com/solutions/signalling/interlocking-40-safe-rail-operations-increased-capacity-and-reliability |access-date=2026-01-15 |website=Alstom |language=en}}</ref>
* [SSI](/source/Solid_State_Interlocking) (Solid State Interlocking) - [British Rail](/source/British_Rail) (BR), [GEC-General Signal](/source/GEC-General_Signal), [Invensys](/source/Invensys), now ''Siemens Mobility''
* Westlock from [Westinghouse](/source/Westinghouse_Electric_Corporation) -> Invensys<ref>{{Cite web |last=Francis |first=John |date= |title=WESTLOCK – Evolving SSI |url=https://www.studocu.com/en-us/document/baptist-university-of-the-americas/cable-details/irse-westlock/64353608 |url-status=live |access-date=2026-01-16 |website=Studocu |publication-date=}}</ref>
* ''ZSB 2000'' from [Scheidt & Bachmann](/source/Scheidt_%26_Bachmann) (Germany)<ref>{{Cite web |title=Interlocking Control System |url=https://www.scheidt-bachmann.de/en/signalling-systems/products-solutions/interlocking-system/interlocking-control-system |access-date=2026-01-16 |website=www.scheidt-bachmann.de}}</ref>

== Interface between different brands ==

When interfacing different brands of CBI equipment, it may be necessary to use relays of each regime, which are then hardwired from one to the other. This happens e.g. in the middle of the [Channel Tunnel](/source/Channel_Tunnel) where French and British signalling equipment meet.

The network division of [Deutsche Bahn](/source/Deutsche_Bahn) (now [DB InfraGo](/source/DB_InfraGO)) has been creating a framework of standard interface definitions under the label ''DSTW'' [<nowiki/>[de](/source/%3Ade%3ADigitales_Stellwerk)] (for "digital" interlocking with full [IPv6](/source/IPv6)-based communication). A project group named [EULYNX](/source/Eulynx) has defined a set of global interface definitions SCI-* (from ''Standard Communication Interface''). These interfaces are defined with RailML terms. Ideally all partnering companies should transform their equipment along these standards and partial mixing of approved suppliers should be possible. The goal was to circumvent vendor lockin and private interfaces. These standards were adopted by other countries like [Denmark](/source/Denmark) and [Norway](/source/Norway) for replacement projects of railway signalling. In [Germany](/source/Germany) the mass rollout has not started in 2025.

== Competition Rules ==

Since only some of the major signalling organisations make CBI equipment, it was agreed that to prevent other players being left out in the cold, CBI equipment would be made available to those players at cost.{{citation needed|date=February 2019}}

== References ==
{{Reflist}}

{{Authority control}}

Category:Interlocking systems
Category:Rail infrastructure

{{rail-transport-stub}}

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Adapted from the Wikipedia article [Computer-based interlocking](https://en.wikipedia.org/wiki/Computer-based_interlocking) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Computer-based_interlocking?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.