In normal driving, how do some drivers use the hand valve to prevent jackknifing?

Using the hand valve, also known as the trailer brake control, can be a beneficial tool for drivers operating combination vehicles, particularly to prevent jackknifing, which is a dangerous situation where the trailer swings out to the side of the towing vehicle. The correct approach is to utilize the hand valve as it is designed to give the driver more precise control over the trailer brakes separate from the vehicle brakes.

When drivers apply the hand valve, they can slow down the trailer independently, which helps to stabilize the combination vehicle and maintain a straight line while decelerating. This method allows drivers to effectively manage the braking power on the trailer without locking up the tractor's brakes, thereby reducing the risk of the trailer swaying out of control and triggering a jackknife scenario.

In contrast, simply relying on the regular brake pedal may not provide the same level of control, especially in slippery conditions or when a quick response is necessary. The hand valve lets the driver modulate the brake pressure applied to the trailer, enabling a smoother stop and maintaining stability throughout the braking process.