SR 3 begins at a diamond interchange with US 101 south of Shelton in unincorporated Mason County on the Olympic Peninsula.^[3] The highway travels north into Shelton at the end of Oakland Bay on 1st Street and crosses over a Puget Sound and Pacific Railroad line and Goldsborough Creek.^[4] SR 3 turns east on Pine Street and leaves Shelton, traveling northeast along Oakland Bay and a US Navy rail line.^[4] The highway continues north along Oakland Bay and Case Inlet past heavily forested areas to Allyn-Grapeview, where it serves as the western terminus of SR 302 at North Mason High School. SR 3 travels towards the southern end of the Hood Canal and intersects the eastern termini of SR 106 and SR 300 in Belfair.^[5] The highway continues northeast past Bremerton National Airport towards the community of Gorst in Kitsap County, where it forms the western terminus of SR 16.^[6][7]

SR 3 becomes a four-lane divided freeway and travels northeast along the Sinclair Inlet to an interchange with SR 304 in Navy Yard City, serving the city of Bremerton and Naval Station Bremerton.^[8] The freeway continues through western Bremerton past the diamond interchange with SR 310 and the community of Chico along Dyes Inlet.^[9] SR 3 travels west of Silverdale past the western terminus of SR 303 at the Kitsap Mall and east of Naval Submarine Base Bangor in Bangor.^[10] The freeway continues north towards Poulsbo past the termini of SR 308 and SR 305, which serve Keyport and Bainbridge Island respectively.^[11][12] SR 3 travels north from Poulsbo as a two-lane road towards Port Gamble and ends at the eastern approach of the Hood Canal Bridge at an intersection with SR 104.^[1][6]

Every year, the Washington State Department of Transportation (WSDOT) conducts a series of surveys on its highways in the state to measure traffic volume. This is expressed in terms of annual average daily traffic (AADT), which is a measure of traffic volume for any average day of the year. In 2011, WSDOT calculated that the busiest section of SR 3 was between SR 16 in Gorst and SR 304 in Navy Yard City, serving 69,000 vehicles, while the least busiest section was southwest of Allyn-Grapeview at an intersection with Grapeview Loop Road, serving 6,600 vehicles.^[13] SR 3 is designated as a STRAHNET corridor within National Highway System, connecting Naval Base Kitsap to the state highway system between Gorst and Bangor, while the rest of the highway is part of the system, which includes roadways important to the national economy, defense, and mobility.^[14][15] WSDOT designates the entire route of SR 3 as a Highway of Statewide Significance,^[16] which includes highways that connect major communities in the state of Washington.^[17]

SR 3 follows the route of a paved section of State Road 21 between Belfair and Port Gamble on the Kitsap Peninsula that was added to the state highway system in 1915.^[18][19] The highway was later split between the Navy Yard Highway from Belfair to Bremerton and State Road 21 from Bremerton to Port Gamble in 1919.^[20] In 1923, the state highway system was restructured and the Navy Yard Highway was numbered as State Road 14, while State Road 21 kept its designation.^[21] The Navy Yard Highway, an unpaved highway connecting Union to Charleston, was dedicated on June 12, 1923.^[22][23]

During the creation of the primary and secondary state highway system in 1937, the paved State Roads 14 and 21 kept their numerical designations and became PSH 14 and PSH 21, respectively. PSH 21 was extended southwest from Bremerton on the former Navy Yard Highway to Gorst, while PSH 14 turned south at Gorst and headed towards Tacoma. A branch of PSH 14, named SSH 14A, was designated on a gravel road that connected the main highway at Belfair to US 101 in Shelton.^[24][25] In 1955, PSH 21 was extended southwest along PSH 14 from Gorst to Union, shortening PSH 14 to its current route as SR 16.^[26][27]

During the 1964 highway renumbering, a new state route system replaced the existing primary and secondary state highways and SR 3 was designated along SSH 14A, PSH 14, and PSH 21 on its present route when it was codified in 1970.^[2][28][29] Construction of the freeway section of SR 3 began in 1963 between SR 304 in Navy Yard City and Silverdale west of Bremerton and was opened in February 1968 at a cost of $2.2 million.^[30][31] The freeway was extended north towards Poulsbo in late 1973,^[32][33] and further north to Naval Submarine Base Bangor in 1981 after the arrival of Ohio-class submarines at Bangor.^[34][35] The Poulsbo section was widened and extended through an interchange with SR 305 in the early 1990s.^[36] The freeway was originally intended to connect with SR 16 (itself upgraded to a freeway in the 1970s and 1980s) with a bridge across the Sinclair Inlet.^[31]

In the 2000s, WSDOT re-built the interchange between SR 3 and SR 303 in Silverdale at a cost of $26 million, paid for by a 2003 gas tax. The new interchange, opened in November 2007, split the western terminus of SR 303 between two exits, signed as 45A and 45B,^[1] and removed a loop ramp that created turning conflicts.^[10][37] WSDOT began study of a Belfair bypass in 1966 and completed a provisional report in 2010 that did not recommend constructing a bypass of the community,^[38] instead opting for a project to widen the highway and add safety improvements that began work in late 2013.^[39] The project was revived later in the decade and is scheduled to be completed by 2026, carrying the new alignment of SR 3 while the existing road remains as a business route through Belfair.^[40][41]

• Highways of Washington State