What indicates a CBTC emergency brake application?

A loss of the Movement Authority Limit (MAL) along with the disk turning red is a clear indicator of an emergency brake application in a Communications-Based Train Control (CBTC) system. The MAL is crucial for maintaining safe train operations, as it defines the maximum distance a train is allowed to travel based on the current operational parameters. When the MAL is lost, it signifies that the train no longer has authorization to proceed, prompting the system to trigger an emergency brake application to stop the train safely. The visual cue of the disk turning red provides an immediate and recognizable warning to operators that an emergency condition is present, reinforcing the need for prompt attention to the situation.

Other options, while they might relate to operational changes or alerts within the train control system, do not specifically represent the condition of an emergency brake application as accurately as the loss of MAL and the corresponding visual indication.