What must be done at road crossings when cars are shoved or a gravity switch move is made?

When cars are shoved or a gravity switch move is made at road crossings, having an employee on the ground to provide warning is essential to ensure safety. This practice helps alert both motorists and pedestrians of the train's movements, particularly since the visibility and timing can be unpredictable during these operations. The presence of a ground employee acts as an additional layer of safety, reducing the risk of accidents and ensuring that vehicles and individuals are aware of the upcoming train movements.

The other options suggest alternative safety measures. However, these may not practically apply in every situation involving road crossings during such maneuvers. For instance, requiring all vehicles to stop completely is not always feasible or necessary if proper warnings are given. Similarly, activating crossing guards or signals may not be appropriate for all types of switch moves and could lead to unnecessary delays or confusion. Thus, the focus on having an employee on the ground to provide direct warning aligns with standard safety protocols in the rail industry.