What is the proper test to determine if hand brakes on a laid-up train will hold on a steep grade?

The proper test to determine if hand brakes on a laid-up train will hold on a steep grade involves releasing the valve. By releasing the valve, the operator can assess whether the hand brakes are effectively maintaining the train's position on the incline. This action simulates the conditions the train would face if it were subjected to the gravitational forces present on a steep gradient.

When the valve is released, the brake system's functionality can be evaluated. If the hand brakes do not hold the train in place, the operator can immediately identify an issue that needs to be addressed before the train resumes operation. This test is crucial for ensuring safety and preventing potential accidents caused by equipment failure on a steep grade.

The other choices do not directly contribute to assessing the effectiveness of the hand brakes. Increasing the throttle would introduce power to the train, which is irrelevant when determining whether the hand brakes are functioning correctly. Engaging the front coupler has no direct relationship with evaluating the hand brake system's holding capacity. Checking the brake lights may indicate whether the system is operational in a general sense but does not specifically test the hand brakes' ability to hold the train on a slope.