Juridical Recorder Unit (JRU)
The Juridical Recorder Unit (JRU) is the onboard black box of an ETCS-equipped train. It records driving and train-control data (speed, brake commands, movement authorities and driver actions) as defined in UNISIG Subset-027, for post-incident investigation and audit.
How it works
The JRU receives a defined set of messages from the onboard ETCS computer (EVC) and stores them in a crash-protected memory with precise timestamps. Recorded data includes the train's position and speed, the movement authorities received, mode changes, brake interventions and driver inputs.
Subset-027 specifies the exact message formats so that data can be downloaded and analyzed with standard tools after an incident or during routine review.
Why it matters for security
JRU data is a trustworthy, standardized record of what the train control system actually did. Ingesting it alongside network monitoring provides ground truth for investigating anomalies, correlating suspected cyber events with operational effects, and supporting forensic analysis on rolling stock.
Related solution
Operating ERTMS across national rail networks
Correlating onboard recorder data with network monitoring for rail-safe investigation.
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