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CITYFLO 650 CBTC

Logo: The original uploader was TorontoStorm at English Wikipedia ., Public domain, via Wikimedia Commons3

Type of railway signalling system

In railway signalling, a moving block is a signalling block system under which the "blocks", or safe zones around trains, are defined in real time by computers. That requires both the knowledge of the exact location and the speed of all trains at any given time, as well as continual communication between the central signalling system and the signalling system in the train cab. Moving block allows trains to run closer together (reduced headway) while maintaining the required safety margins, thereby increasing the line's overall capacity.2 Wikipedia text CC BY-SA 4.0

Last updated Oct 21, 2026.

Overview

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In railway signalling, a moving block is a signalling block system under which the "blocks", or safe zones around trains, are defined in real time by computers. That requires both the knowledge of the exact location and the speed of all trains at any given time, as well as continual communication between the central signalling system and the signalling system in the train cab.2

Products and brands

"Moving block" is not technically a standard. It is a concept that can be implemented using various standards.

CBTC

CBTC is the most common associated standard. However, CBTC, as it is described in IEEE 1474 (1999), makes no mention of a requirement for moving block operation. That said, the overwhelming majority of moving block systems use a signalling system consistent with the IEEE 1474 (1999) standard. Many different manufacturers create systems consistent with the IEEE 1474 standard, but very few of them (if any) are compatible with each other.

Thales Seltrac

Bombardier CITYFLO (various versions)

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Alstom Urbalis (various versions)

Siemens Trainguard MT CBTC

Nippon Signal SPARCS

Invensys Sirius

Argenia SafeNet CBTC

CAF Optio CBTC Option Solution

TBTC

Transmission-based Train Control (TBTC) is an earlier form of CBTC that used induction loops on the track for communication with the signalling system, rather than radio signals or some other method. The words "transmission" and "communication" are synonyms in some circumstances, so neither one of those names accurately describes what each standard is. Systems considered to use TBTC are:

London Underground Jubilee Line

Docklands Light Railway

Positive Train Control The US standard for a modern train protection system is considered by some to be an example of TBTC; however it potentially is better described as an Automatic Train Protection system, though "advanced" versions exist that allow for moving block signalling.

ETCS

ETCS is the signalling protocol for the European Rail Traffic Management System (ERTMS). That system is commonly known to have three levels: Level 1 (an ATP system only); Level 2 (a virtual block system that can also be provided with Automatic Train Operation (ATO)); and Level 3 (similar to Level 2 but uses moving block and can do away with a lot of the lineside equipment). In practice, level 3 is not yet used, and has become an extension of Level 2. Equipment is produced by various manufacturers, but that standard has protocols, so all ETCS equipment is compatible, unlike CBTC systems.

From Wikipedia’s article on Cityflo 650 CBTC, shared under CC BY-SA 4.0.4

Sources

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