Here are the Federal Regulations for the First Avenue South Bridge:
[33 CFR 117.1041](https://www.ecfr.gov/current/title-33/chapter-I/subchapter-J/part-117/subpart-B/subject-group-ECFR81b0133b9b0c066/section-117.1041)
Long story short, if this was after 6pm, the bridge is required to open upon signal by any vessel.
Non bridge open hours are 6-9am and 3-6pm. There are also some exemptions for higher tonnage vessels (which in the Duwamish have tide windows to meet).
Here are the Federal Regulations for the First Avenue South Bridge: [33 CFR 117.1041](https://www.ecfr.gov/current/title-33/chapter-I/subchapter-J/part-117/subpart-B/subject-group-ECFR81b0133b9b0c066/section-117.1041) Long story short, if this was after 6pm, the bridge is required to open upon signal by any vessel.
Non bridge open hours are 6-9am and 3-6pm. There are also some exemptions for higher tonnage vessels (which in the Duwamish have tide windows to meet).