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Override

In the context of ERTMS (European Rail Traffic Management System), “override” is a specific functionality that allows the driver to bypass certain restrictions imposed by the system under particular circumstances. This functionality is critical in scenarios where normal operations are hampered by system failures or unusual situations, such as when a balise or track circuit is defective.

Key aspects of override in ERTMS:

1. Purpose:
  • To allow the train to proceed under specific conditions where the automatic system would otherwise prevent movement.
  • Typically used in ERTMS levels 1 and 2 when errors or faulty equipment (e.g., balises, track circuits) occur.
2. Usage scenarios:
  • Passing a danger signal (SPAD) with clearance (e.g., during degraded mode operations).
  • Passing a balise that signals the train has stopped but is known to be defective.
  • Moving into areas where the train is unable to establish a reliable connection with the radio block center (RBC).
3. Process initiated by the driver:
  • The driver agent must manually activate the override function using the train’s on-board system (e.g., via the driver-machine interface or DMI).
  • The process usually requires explicit confirmation to avoid accidental activations.
4. Safety measures:
  • Override maneuvers are accompanied by strict safety protocols to reduce risk.
  • Speed restrictions are often imposed during overrun operations (e.g., in some scenarios the maximum limit is 40 km/h).
  • Train movement is closely monitored, either through degraded on-board systems or backup safety mechanisms.
5. Operational levels:
  • Level 1: override can be used to overcome a faulty balise that transmitsa “stop” signal.
  • Level 2: The ‘override allows movement in situations where the RBC is unable to establish communication with the train or the system is in a degraded state.
6. Stages of override activation (workflow example):
  • The driver agent receives a stop command or detects a faulty scale/signal.
  • The driver agent contacts the traffic control center to obtain permission to use the override.
  • Once permission is obtained, the conducting agent activates the override mode via the DMI.
  • The train operates under restricted conditions (e.g., limited speed) until normal operation is restored.

Considerations:

Safety first: Override is not a standard operating procedure, but an emergency measure to deal with system failures.
Recording and monitoring: All override activations are recorded in the train’s on-board systems for later review and analysis.
Training: Train drivers are extensively trained to understand when and how to use the override feature while ensuring safety.

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