This from King County Metro Transit:
King County Metro Transit bus routes will operate with a Sunday schedule on Thursday, July 4, for Independence Day, and many routes will be redirected around community celebrations around the county. Changes also are in store for the South Lake Union Streetcar and water taxis.
The holiday schedule means many commuter bus routes will not be in service that day. Bus riders should check the schedule for their routes, as well as scheduled event and celebration reroutes. Sunday fares are in effect on all Metro routes on July 4.
All Metro offices, including the Customer Information phone lines, will be closed on Thursday in observance of the holiday. When the Customer Information Office is closed, most transit information and the trip planner are available on Metro Online.
South Lake Union Streetcar – Fourth of July service
Some added evening service is planned for the South Lake Union Streetcar before and after the fireworks show on Thursday, July 4th. From 10 a.m. to 7 p.m., service is scheduled every 15 minutes. From about 7:30 p.m. until about 10:15 p.m. (fireworks show time), the streetcar will operate every 10-15 minutes, with service stopping temporarily during the fireworks show to better position streetcars at South Lake Union Park to carry passengers exiting the event. After the fireworks show, southbound streetcars will only travel non-stop to the Westlake hub, and return non-stop to South Lake Union to pick up additional customers exiting the event. Service will conclude by midnight. A route map is online.
The King County Water Taxi between downtown Seattle and West Seattle will operate with a Sunday schedule on July 4, as will the free Water Taxi shuttles – Routes 773 and 775. There will be no service on the Vashon Water Taxi route on Thursday. Go online to see water taxi service details.