Communications-Based Train Control (CBTC)
Communications-Based Train Control (CBTC) is a railway signaling system that locates each train through continuous radio data exchange between trains and wayside equipment, rather than track circuits. This enables moving-block operation: trains run at shorter, dynamically calculated headways, increasing line capacity. Used mainly in metro and urban rail.
How it works
Each train continuously computes its own position using onboard odometry corrected by trackside reference points, and reports it over a train-to-wayside radio link. A zone controller uses these reports to issue each train a movement authority, the distance it may safely travel, and recalculates it in real time as trains move.
Because separation is enforced by data rather than by fixed track blocks, trains can follow one another more closely (moving block). CBTC systems are graded by their degree of automation, from GoA1 (manual driving with protection) through GoA4 (unattended, driverless operation).
Why it matters for security
CBTC replaces isolated trackside circuits with a continuous wireless data network linking onboard and wayside systems. That network is what keeps trains safely separated, which also makes it a safety-critical attack surface. Interference with the radio link, the zone controller, or the integrity of position and authority messages can degrade or halt service, so CBTC deployments are a primary focus of rail OT security monitoring.
Related solution
Securing CBTC systems without disrupting automation
How CylusOne monitors zone-controller and onboard traffic passively, without interfering with certified behavior.
See the solution →
