What sound signal is used when requesting an opening for the Spokane Street Bridge?

When requesting an opening for the Spokane Street Bridge, the proper sound signal is three prolonged blasts, indicated by 1 PL - 3S. This pattern of three prolonged blasts is a universally recognized signal in the maritime community, designed to clearly inform vessels that a bridge is about to open.

Using three prolonged blasts ensures that all nearby vessels are alerted, providing them adequate time to respond and position themselves safely as the bridge opens. This method enhances safety for both the vessels and the bridge operation, facilitating smooth traffic flow in a busy area.

The other signal combinations, while having their own specific meanings, do not correspond to the standard signaling protocol for requesting a bridge opening in this context. Thus, understanding the significance of sound signal patterns is critical for effective communication and operational safety in navigation situations involving movable bridges like the Spokane Street Bridge.