What whistle signal is utilized for calling for a signal?

The correct choice for the whistle signal used to call for a signal is characterized by four long blasts. This specific whistle sequence is standardized within railroad operations to convey clear and unambiguous commands, ensuring effective communication between train engineers and signal personnel.

Using four long blasts indicates a request for a signal, allowing engineers to communicate their need for operational information as they approach signaling points. Such clarity is crucial in maintaining safety and adherence to schedules within the train network.

In contrast, other signals, such as one long blast, typically indicate different operations or commands that do not pertain to requesting a signal. For example, a single long blast might be used to signal departure or alerting other trains in the vicinity but not specifically to indicate a need for a signal. Therefore, recognizing and understanding the specific usage of these signals is vital for effective train control and safety procedures.