What indications signal an emergency brake application in CBTC?

The indication of an emergency brake application in Communications-Based Train Control (CBTC) systems is signaled by a loss of Maximum Allowed Speed (MAL) accompanied by a red disk. The MAL represents the highest speed that a train is permitted to travel, and when this is lost, it typically indicates a situation requiring immediate action, often resulting in the application of the emergency brakes.

When the disk turns red, it visually communicates to the engineer and the systems in control that there is an urgent need to stop the train safely and promptly. This visual cue, coupled with the loss of MAL, is designed to ensure that the operator is fully aware of the critical situation at hand and can take necessary actions to protect passengers and the train.

Other choices do not accurately reflect the indicators used in an emergency braking scenario within a CBTC framework. For instance, if all lights turn green, it generally suggests normal operations rather than an emergency condition. A beep from the control panel might signify alerts or notifications, but it is not a definitive indication of an emergency brake application. Lastly, a gradual reduction in speed does not align with the urgent nature of an emergency stop, where immediate braking is required to halt the train as quickly as possible.