What is not permissible while operating a Ground Motor Vehicle?

Using a cell phone while operating a ground motor vehicle is deemed not permissible due to the significant safety risks it poses. When drivers are distracted by their phones, their attention is diverted from the road and their surroundings, leading to potential accidents and injuries. In a ramp environment, where there is heavy foot and vehicle traffic, maintaining full focus is critical to ensure the safety of all personnel and equipment.

The other options involve safety features or practices that are encouraged or required. Having an open cab can refer to specific vehicle designs that are permitted in certain situations; using turn signals is essential for indicating intentions to other drivers and ensuring clear communication in busy areas; and having seat belts is a standard safety requirement to protect operators in the event of a collision.