Why is it advised not to use the trailer hand valve while driving?

Using the trailer hand valve while driving is advised against primarily because it can cause the trailer to skid. The hand valve, often referred to as the trailer brake, is designed to apply brakes specifically to the trailer. When this valve is engaged, it can lead to an imbalance in braking forces between the truck and the trailer. In certain situations, especially on slick or uneven surfaces, this can cause the rear of the trailer to skid or sway, which compromises the stability and control of the entire rig. Maintaining control of both the tractor and the trailer is crucial for safe driving, and unintentional skidding can lead to accidents, loss of control, or jackknifing.

The other options, while they may relate to vehicle operation, do not directly address the critical safety aspect of braking improperly with the trailer hand valve during driving. For instance, increases in fuel consumption, reduction in engine power, or sudden acceleration are not primary concerns associated with the improper use of the hand valve while actively driving a vehicle. The focus should always be on maintaining safe control of the vehicle, which is why avoiding the use of the trailer hand valve is emphasized.