Which of the following can trigger an Emergency brake application on the Safety Loop?

The choice of the Coupler Fault Relay as a trigger for an Emergency brake application on the Safety Loop is valid because this part of the system is designed to ensure the safety of the train's operation. When a significant fault is detected in the coupler system—such as a failure in the mechanical connection between railcars—it can pose an immediate risk to the integrity of the train and its passengers. By activating the Emergency brake through the Safety Loop, the system prevents potential accidents by ensuring that the train comes to a stop quickly and safely in response to such a critical issue.

In contrast, while the other options have their roles in monitoring various aspects of train operation, they do not directly trigger an emergency brake application on the Safety Loop in the same critical manner. A Train Speed Monitor primarily regulates and monitors the speed for operational purposes, rather than issuing emergency commands. The Passenger Door Sensor is essential for safety regarding door operation but generally does not trigger an emergency stop unless it detects an unsafe condition related to the doors. The Automatic Signal Alert serves to inform the train crew of signal changes, but it does not intrinsically invoke an emergency brake scenario. Therefore, the Coupler Fault Relay stands out as the most appropriate trigger for an emergency brake application due to its critical