Which component is controlled by the trailer hand brake?

The trailer hand brake is designed to control both the emergency and service braking systems of a trailer. When a driver engages the hand brake, it applies the brakes on the trailer, effectively allowing for greater control, especially when parking or performing maneuvers.

The hand brake is particularly useful in preventing the trailer from rolling when it is parked on an incline, and it ensures that it decelerates effectively in emergency situations when needed. This dual capability makes it a crucial safety feature for truck and trailer operators, enabling them to manage braking more safely and efficiently.

In terms of the other options, the service line refers specifically to the supply of air that operates the service brakes under normal conditions, while the emergency brakes have a separate function strictly for stopping the vehicle in a critical situation. Some might think that the hand brake should only control one or the other, but understanding that it manages both systems enhances a driver's ability to operate large vehicles with trailers more safely. It's also important to note that using the hand brake appropriately is generally recommended, especially in situations where maintaining vehicle stability is essential.