How many control devices are required to operate all brakes on trailers?

To operate all brakes on trailers, only one control device is required. This is typically the brake controller, which allows the driver to control the braking system of the trailer from the towing vehicle. A single control device efficiently engages the brakes when needed, ensuring a smooth and coordinated stop. This simplicity is particularly important for ease of operation and safety while towing, as multiple control devices could complicate the braking process and increase the potential for errors.

Other options suggesting two, three, or four devices are not necessary for the basic operation of trailer brakes. The regulatory framework and design standards for trailer brakes ensure that one adequately placed control device can manage the system effectively without redundancy.