What indicates that stopping is necessary for a school bus?

The indication that stopping is necessary for a school bus is marked by the activation of flashing red lights and stop arms. When a school bus stops to allow children to board or exit, these lights and arms serve as critical visual signals for other drivers on the road. The flashing red lights alert approaching vehicles that they must stop, as children may be crossing the street or walking near the bus. The extended stop arms create a physical barrier, further emphasizing the necessity for vehicles to halt their approach.

Understanding this mechanism is vital for ensuring the safety of students as they navigate around school buses. It's crucial for drivers to recognize the legal requirement to stop when these signals are present, as failing to do so can result in severe penalties, and more importantly, can endanger children. The other options, such as passengers boarding or flashing yellow lights, do not convey an immediate need to stop; rather, they represent different stages of bus operation and safety protocols.