How can you determine if the brakes have applied or released on the rear car during a test?

The correct answer involves checking the end-of-train telemetry device, which is designed to provide real-time information about various aspects of the train, including the brake status of the rear car. This telemetry system can relay critical data back to the locomotive, allowing the crew to confirm whether the brakes are applied or released without needing to physically inspect the rear car.

Using the end-of-train telemetry device is particularly advantageous as it offers immediate feedback, facilitating quick decision-making and ensuring that safety protocols are maintained. The technology enhances operational efficiency by eliminating the need for manual checks, which can be time-consuming and may introduce opportunities for human error.

In contrast, other options such as visually checking brake lights or measuring temperature changes at the rear wheel provide indirect evidence that may not be reliable in determining the precise status of the brakes. A manual brake test, while effective in confirming functionality, can be more labor-intensive and may not always be feasible in every situation. Thus, relying on the telemetry device streamlines the process and enhances operational safety.