How can a driver check their air brake system before a trip?

Performing a brake test to ensure functionality is an essential step for a driver to verify the operational state of the air brake system before embarking on a trip. This test helps confirm that air pressure is building up correctly, that the brakes are responding as intended, and that there are no leaks in the system. By doing a brake test, a driver can assess both the service brakes and the emergency brakes, ensuring that they meet safety standards and can effectively stop the vehicle when necessary.

Other options serve different purposes but do not specifically address the functionality of the air brakes. Checking the horn, while useful for communication, does not impact the operation of the braking system. Evaluating tire pressure is important for overall vehicle safety but is not a direct test of the brakes. Inspecting the cargo area is crucial for load security and balance but does not involve assessing the braking mechanism itself. Thus, conducting a brake test is the most relevant and critically needed action to ensure that the air brake system is properly functioning before hitting the road.