Why is it important to lock the tractor glad hands together when not towing a trailer?

Locking the tractor glad hands together when not towing a trailer is important primarily to keep dirt and water out of the lines. The glad hands connect the air supply lines between the tractor and trailer, which are crucial for proper operation of the braking system. If these lines are left exposed, debris, moisture, or contaminants can enter, potentially damaging the air lines or affecting the braking performance when a trailer is attached again. By connecting the glad hands, you create a safeguard against these foreign particles, ensuring that the air system remains clean and functional. This practice helps maintain the safety and reliability of the vehicle's braking system during operational downtime.