What should you do after supplying air to a trailer to ensure safety?

After supplying air to a trailer, ensuring that the air lines are not crossed is crucial for safety. When connecting the trailer to the tractor, proper routing of the air lines ensures that the braking system will operate effectively. If the air lines are crossed, it can lead to a potentially dangerous situation where the brakes may not engage correctly, causing a loss of control while driving. This step is vital as it directly impacts the functionality of the trailer's brakes, which are essential for safe operation on the road.

Checking the air pressure gauge, inspecting the trailer tires, and performing a visual inspection of the trailer are certainly important safety checks but they do not specifically address the immediate concerns related to air supply and proper function of the braking system. Ensuring that the air lines are correctly connected helps prevent operational failures that may arise if the air supply is incorrectly configured.