What is the primary purpose of the stop arm on a school bus?

The primary purpose of the stop arm on a school bus is to signal to other drivers that they must stop. When the stop arm is extended, it serves as a clear and unmistakable indicator that the bus is in the process of loading or unloading students. This is crucial for the safety of the children entering or exiting the bus, as it creates a designated zone where they can safely board or disembark without the risk of injury from passing vehicles.

The stop arm is designed to be highly visible, making it evident to drivers that they need to halt their vehicles and allow students to cross the street safely. This functionality is reinforced by state laws, which mandate that vehicles must stop when a school bus has its stop arm extended.