Which of the following actions is prohibited regarding seat belts in commercial vehicles?

The correct answer is the action of removing the seat belt during travel. In commercial vehicles, it is imperative that all occupants wear their seat belts at all times while the vehicle is in motion. This requirement is a critical safety measure aimed at reducing the risk of injury during accidents or sudden stops. Seat belts are designed to keep the driver and passengers securely in their seats, thus preventing ejections from the vehicle and minimizing movement within the cab during a collision.

While seat belts can be worn in various scenarios, such as when reversing, the act of removing a seat belt while the vehicle is traveling compromises safety. It can lead to severe consequences in the event of an accident. Similarly, using additional harnesses, if not properly integrated, could also be unsafe, but it doesn't directly violate seat belt laws in commercial contexts. Wearing the seat belt at all times is a law that is strictly enforced for the safety of all individuals in the vehicle.