When first posted as such in January 1964, SR 305 began at the State Ferry Terminal in Winslow and headed NNW, crossing the Agate Pass Bridge from Bainbridge Island to the Kitsap Peninsula. From the bridge, SR 305 headed NW to Jct SR 3 at Poulsbo, where SR 305 ended. Winslow had been a town (small city) centered around the ferry terminal. Most of Bainbridge Island was part of unincorporated Kitsap County. In 1990, Winslow annexed the remainder of Bainbridge Island. The Town of Winslow then changed its name to the City of Bainbridge Island. At the Poulsbo end of SR 305 the highway was extended about a half mile in the early 1990s when an interchange was built with a new SR 3 freeway. The Seattle-Bainbridge Island ferry route was explicitly made a part of SR 305 by the state legislature in 1994. Today, SR 305, minus the ferry route, is 13.50 miles long.
Before 1964, SR 305 had been SSH 21A.
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