What is the primary function of a parking brake control in the cab?

The primary function of a parking brake control is to engage the brakes to secure the vehicle when it is parked, preventing it from rolling away. This is particularly important for large commercial vehicles, as they can be difficult to manage if they start to move unintentionally. The parking brake typically operates by applying the brakes through a mechanical linkage or by activating an air brake system in air-braked vehicles.

When the parking brake control is activated, it releases air pressure in the brake lines, allowing the brakes to engage and hold the vehicle in place. This ensures safety when the vehicle is parked, especially on inclines or uneven surfaces.

The other functions listed do not pertain to the operation of the parking brake. Controlling vehicle speed relates to the accelerator and service brakes, engaging the air compressor is part of maintaining the air pressure system but is not directly related to parking, and monitoring fuel levels pertains to the fuel gauge rather than the brake system.