Which sound signal should be used for opening the Duwamish River Railroad Bridge?

The correct choice for the sound signal to be used for opening the Duwamish River Railroad Bridge is one prolonged blast followed by one short blast (1 PL - 1S). This signaling method is consistent with the guidelines established by the United States Coast Guard and the relevant maritime navigation rules.

In situations involving drawbridges, the use of sound signals serves to communicate specific intents to vessels navigating nearby waters. The prolonged blast signifies the intention to open the bridge, while the short blast serves as a follow-up to indicate that the opening process has been initiated and to signal an awareness of the operation to vessels in the vicinity.

This particular combination of signals ensures clarity and promotes safety, as it effectively informs boat operators of the bridge's status and future actions. In maritime operations, clear communication through sound signals helps prevent misunderstandings that could lead to hazardous situations in navigable waters.

Other signal combinations, such as solely prolonged signals or different variations of short signals, do not correlate with the recognized signaling practices for drawbridges, making them less appropriate in this specific context.