What triggers emergency braking in an ETCS Level 1 system?

In an ETCS (European Train Control System) Level 1 system, an emergency brake application is triggered when the train exceeds the permitted speed or approaches a signal at danger (red) without appropriate braking, as determined by the balise data read by the train. ETCS Level 1 is a train protection system that uses trackside signals and Eurobalises (transponders) to transmit information to the train. The balises are located at specific points along the track and transmit data about the permitted speed, signal aspects (indications), and other relevant information to the train's onboard computer. The onboard computer continuously monitors the train's speed and location and compares it to the information received from the balises. If the train exceeds the permitted speed or approaches a signal at danger without the driver initiating appropriate braking, the onboard computer will automatically trigger an emergency brake application to stop the train before it reaches a point where a collision or other hazardous situation could occur. This system is designed to prevent train accidents caused by human error, such as speeding or failing to observe signals. The specific braking curves and intervention thresholds are precisely calculated and programmed into the onboard computer to ensure that the train stops safely within the available braking distance. The system relies on the driver to primarily control the train, but provides a safety net to prevent accidents if the driver makes a mistake.