Final answer:
The question seems to inquire about the conditions under which a train operator is not required to receive a buzzer signal to start the train. While the provided text references the Doppler effect, more context is needed to answer this railroad operation question accurately.
Step-by-step explanation:
The question revolves around the scenario where a train operator is required to wait for a buzzer signal before starting the train in addition to a starting light, except in certain conditions. The inquiry seems to be focused on understanding under what circumstances the buzzer signal is not necessary for the train to start. The provided texts seem to reference concepts of motion and sound, potentially relating to the Doppler effect, which is a phenomenon observed when there is relative motion between an observer and a sound source. However, these references in the question snippet do not provide enough context to directly answer the student's question. Instead, they touch upon the principles of physics that might be tangentially related to train operations and signals. Generally, in train operations, a buzzer might not be required if there are clear visual cues or other redundant safety systems in place that ensure safe operation without the need for auditory confirmation.