CBTC Acronyms & Glossary
202 terms, organized by subsystem rather than alphabetically — because that is how they arrive. When an RFP starts describing the Data Communication System, six related terms follow within the same paragraph. Read by section and the vocabulary builds itself; use it alphabetically and you learn definitions without learning how the words relate.
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What's inside
- 202 terms across 11 sections, each defined in one or two sentences.
- Core subsystems: ATP, ATO, ATS, zone controller, VOBC, DCS and the rest of the architecture.
- Separation and capacity: movement authority, end of authority, moving block, headway, TPHPD, braking curve.
- Position and odometry, including why three sensor types are fused and what balises are actually for.
- All five GoA levels plus the operating and degraded modes that surround them.
- Safety and assurance: SIL, THR, vital and non-vital, the safety case, 2oo2 and 2oo3 architectures.
- Standards, procurement, testing and the external systems outside the IEC 62290 boundary.
- Where two terms are commonly confused — PTC and CBTC, fixed and virtual block, FTA the analysis and FTA the agency — the entries say so.
Why it is not alphabetical
An alphabetical glossary is easy to search and useless to learn from. It puts axle counter next to ATS and separates movement authority from end of authority, which is exactly backwards: those two terms only make sense together. This sheet groups terms the way the work presents them — subsystems, then separation, then position, then communications, then automation grades, then assurance, standards, procurement, testing and interfaces. Read a section end to end and you have the vocabulary for one conversation.
The confusions worth pre-empting
A few pairs cause most of the misunderstanding in US practice. PTC and CBTC are not variants of one another: PTC is fixed-block mainline overspeed enforcement under a different regulator, and calling a CBTC project "PTC for metros" will mislead everyone in the room. FTA means Fault Tree Analysis to a safety engineer and the Federal Transit Administration to a program manager, often in the same meeting. Vital and non-vital is not a synonym for important and unimportant — ATS is non-vital and indispensable. And SIL 4 is a design posture with an evidence burden, not a certificate a supplier holds.
Sources & method
Compiled by Chunjun (Francisco) Wang from the vocabulary used across Communications-Based Train Control, Volumes 1 and 2. Definitions are deliberately short — the long-form treatment of each concept is in the book. Where usage differs between suppliers or between US and international practice, the entry says which is which.