Three primary, and four auxiliary routes make up the Washington state segment of the Interstate Highway System

Interstate Highway System

The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

, totaling 764.27 miles (1,230 km).The mileage is a sum of the lengths listed and cited on this page. These highways connect every city in the state with a population of over 100,000: Seattle

Seattle, Washington

Seattle is the county seat of King County, Washington. With 608,660 residents as of the 2010 Census, Seattle is the largest city in the Northwestern United States. The Seattle metropolitan area of about 3.4 million inhabitants is the 15th largest metropolitan area in the country...

, Spokane

Spokane, Washington

Spokane is a city located in the Northwestern United States in the state of Washington. It is the largest city of Spokane County of which it is also the county seat, and the metropolitan center of the Inland Northwest region...

, Tacoma

Tacoma, Washington

Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...

, Vancouver

Vancouver, Washington

Vancouver is a city on the north bank of the Columbia River in the U.S. state of Washington. Incorporated in 1857, it is the fourth largest city in the state with a 2010 census population of 161,791 as of April 1, 2010...

, Bellevue

Bellevue, Washington

Bellevue is a city in the Eastside region of King County, Washington, United States, across Lake Washington from Seattle. Long known as a suburb or satellite city of Seattle, it is now categorized as an edge city or a boomburb. The population was 122,363 at the 2010 census.Downtown Bellevue is...

, and Everett

Everett, Washington

Everett is the county seat of and the largest city in Snohomish County, Washington, United States. Named for Everett Colby, son of founder Charles L. Colby, it lies north of Seattle. The city had a total population of 103,019 at the 2010 census, making it the 6th largest in the state and...

, as well as the state capital, Olympia

Olympia, Washington

Olympia is the capital city of the U.S. state of Washington and the county seat of Thurston County. It was incorporated on January 28, 1859. The population was 46,478 at the 2010 census...

.

Interstate 90

Interstate 90 in Washington

Interstate 90 , a transcontinental Interstate Highway from Seattle, Washington, to Boston, Massachusetts, crosses the state of Washington before crossing the Idaho state line between Spokane and Post Falls...

 (I-90) is the longest primary Interstate Highway in Washington measuring 297.52 mi (478.8 km), while I-82

Interstate 82

Interstate 82 is a Interstate Highway that extends from I-90 in Ellensburg, Washington to I-84 near Umatilla, Oregon in the United States. In the state of Washington, it serves the cities of Ellensburg, Yakima, and the Tri Cities , and in Oregon, it serves Umatilla and Hermiston...

 is the shortest at 132.57 mi (213.4 km). The longest auxiliary Interstate Highway in Washington is I-405

Interstate 405 (Washington)

Interstate 405 in Washington is a stretch of freeway that bypasses Seattle east of Lake Washington. The northern terminus is in Lynnwood and the southern terminus is in Tukwila...

 at 30.3 mi (48.8 km), and the shortest is I-705

Interstate 705

Interstate 705 is a short Interstate Highway spur route of Interstate 5 located entirely within Tacoma, Pierce, Washington, United States. I-705 serves as the connector between Interstate 5, Downtown Tacoma, Tacoma's waterfront, North Tacoma, and the Tacoma Dome...

 at 1.5 mi (2.4 km). One route, I-605

Interstate 605 (Washington)

Interstate 605 is the common designation given to several proposals for a new auxiliary route of the Interstate Highway System bypassing Interstate 5 and I-405 in the US state of Washington. Proposals have been heard from since the 1960s, including highways connecting from I-5 all the way to the...

, has been proposed over the years to form another bypass around I-5 and I-405, however there are no plans to construct this fifth auxiliary route.

Primary Interstate Highways

Route	Length	Description	Southern / western terminus	Northern / eastern terminus	References
		I-5 enters the state from Oregon Oregon Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern... , traveling north past the interchange with I-205 and through rural southwestern Washington. The highway passes the state capital Olympia, and turns northeast through Tacoma and I-705, before turning back north. I-405 is intersected, which serves the Eastside Eastside (King County, Washington) File:Seattle-lakewashington-lakesammamish.PNG|250px|right|The Eastside is to the right of Seattle.# rough city boundariespoly 137 256 148 256 158 194 172 179 172 237 212 266 133 266Renton... , as I-5 enters Seattle. After exiting Seattle, I-5 intersects I-405 again and heads towards Everett and meets the Canada – United States border in Blaine.	I-5 Interstate 5 in Oregon In the U.S. state of Oregon, Interstate 5 traverses the state from north to south, passing through the major cities of Portland, Salem, Eugene, and Medford.-Route description:...  at the Oregon state line	BC 99 at the Canada – United States border
		I-82 begins at an intersection with I-90 outside of Ellensburg, heading southeasterly by the Yakima Training Center Yakima Training Center The Yakima Training Center is a United States Army training center located in south central Washington state. It is bounded on the west by Interstate 82, on the south by the city of Yakima, on the north by the city of Ellensburg and Interstate 90, and on the east by the Columbia River...  and the city of Yakima, paralleling the Yakima River Yakima River The Yakima River is a tributary of the Columbia River in south central and eastern Washington State, named for the indigenous Yakama people. The length of the river from headwaters to mouth is , with an average drop of .-Course:... . I-82's sole auxiliary route, I-182, serves the Tri-Cities as I-82 and continues south into Oregon.	I-90 in Ellensburg	I-82 at the Oregon state line
		I-90 begins just west of an interchange with I-5 in Seattle, heading east over floating bridges to Mercer Island and Bellevue, before traveling through more rural Western Washington, crossing the Cascade Mountains over Snoqualmie Pass Snoqualmie Pass Snoqualmie Pass is a mountain pass that carries Interstate 90 through the Cascade Range in the U.S. State of Washington. The elevation of the pass summit is , and is on the county line between Kittitas County and King County...  before dropping into Eastern Washington at Ellensburg. I-82 is intersected outside of Ellensburg as the highway continues east through rural Eastern Washington before turning northeasterly and intersecting Spokane before leaving the state into Idaho Idaho Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state.... .	SR 519 in Seattle	I-90 Interstate 90 in Idaho In the U.S. state of Idaho, Interstate 90 has a small routing in the panhandle, just under 74 miles . Traveling east from Spokane, Washington, I-90 passes through Post Falls and Coeur d'Alene, over Fourth of July Summit, and through the Silver Valley before entering Montana at Lookout Pass.I-90 is...  at the Idaho state line

Auxiliary Interstate Highways

Route number	Length	Western / southern terminus	Eastern / northern terminus	Counties	Description	References
		at the Oregon Oregon Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...  state line	in Salmon Creek Salmon Creek, Washington Salmon Creek is a census-designated place in Clark County, Washington, United States. The population was 16,767 at the 2000 census.-Geography:Salmon Creek is located at ....	Clark Clark County, Washington Clark County is a county located in the southwestern part of the U.S. state of Washington, across the Columbia River from Portland, Oregon.Clark County was the first county of Washington, named after William Clark of the Lewis and Clark Expedition...	I-205 starts on the Glenn L. Jackson Memorial Bridge Glenn L. Jackson Memorial Bridge The Glenn L. Jackson Memorial Bridge, or I-205 bridge, is a segmental bridge that spans the Columbia River between Vancouver, Washington and Portland, Oregon....  over the Columbia River Columbia River The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...  at the Oregon Oregon Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...  state line in Vancouver Vancouver, Washington Vancouver is a city on the north bank of the Columbia River in the U.S. state of Washington. Incorporated in 1857, it is the fourth largest city in the state with a 2010 census population of 161,791 as of April 1, 2010... . From Vancouver, I-205 goes northwest to I-5 in Salmon Creek Salmon Creek, Washington Salmon Creek is a census-designated place in Clark County, Washington, United States. The population was 16,767 at the 2000 census.-Geography:Salmon Creek is located at .... .
		in Tukwila Tukwila, Washington Tukwila is a city in King County, Washington, United States. The northern edge of Tukwila borders the city of Seattle. The population was 19,107 at the 2010 census.-History:...	in Lynnwood Lynnwood, Washington Lynnwood is a city in Snohomish County, Washington, United States. The population was 35,836 at the 2010 census, making it the fourth largest in Snohomish County and twenty-ninth largest in Washington State. The city is a mix of urban, suburban, small city, crossroads and bedroom community to many...	King King County, Washington King County is a county located in the U.S. state of Washington. The population in the 2010 census was 1,931,249. King is the most populous county in Washington, and the 14th most populous in the United States.... , Snohomish Snohomish County, Washington Snohomish County is a county located in the U.S. state of Washington. It is named after the Snohomish tribe. Since 2000, the county's population has grown from 606,024 to 713,335 residents , making it one of the fastest-growing in the state, ranking third in overall population after King and...	I-405 starts at I-5 near the SeaTac International Airport in Tukwila Tukwila, Washington Tukwila is a city in King County, Washington, United States. The northern edge of Tukwila borders the city of Seattle. The population was 19,107 at the 2010 census.-History:... . I-405 goes east to Renton Renton, Washington Renton is an Eastside edge city in King County, Washington, United States. Situated 11 miles southeast of Seattle, Washington, Renton straddles the southeast shore of Lake Washington. Founded in the 1860s, Renton became a supply town for the Newcastle coal fields... , where it intersects with SR 167. Then, it goes north to Bellevue Bellevue, Washington Bellevue is a city in the Eastside region of King County, Washington, United States, across Lake Washington from Seattle. Long known as a suburb or satellite city of Seattle, it is now categorized as an edge city or a boomburb. The population was 122,363 at the 2010 census.Downtown Bellevue is... , where it intersects I-90 and SR 520 before going northwest to I-5 in Lynnwood Lynnwood, Washington Lynnwood is a city in Snohomish County, Washington, United States. The population was 35,836 at the 2010 census, making it the fourth largest in Snohomish County and twenty-ninth largest in Washington State. The city is a mix of urban, suburban, small city, crossroads and bedroom community to many... .
					I-605 is an oft-proposed, but never constructed bypass of I-405 and I-5.
		in Tacoma Tacoma, Washington Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...	Schuster Parkway in Tacoma	Pierce Pierce County, Washington right|thumb|[[Tacoma, Washington|Tacoma]] - Seat of Pierce CountyPierce County is the second most populous county in the U.S. state of Washington. Formed out of Thurston County on December 22, 1852, by the legislature of Oregon Territory...	I-705 begins at I-5/SR 7 and goes north to the Schuster Parkway.
		near Richland Richland, Washington Richland is a city in Benton County in the southeastern part of the U.S. state of Washington, at the confluence of the Yakima and the Columbia Rivers. As of the 2010 census, the city population was 48,058. April 1, 2011 estimates from the Washington State Office of Financial Management put the...	in Pasco Pasco, Washington Pasco is a city in and the county seat of Franklin County, Washington, United States.Pasco is one of three cities that make up the Tri-Cities region of the state of Washington...	Benton Benton County, Washington Benton County is a county located in the south-central portion of the U.S. state of Washington. The Columbia River makes up the north, south, and east boundaries of the county. In 2010, its population was 175,177. The county seat is Prosser, and its largest city is Kennewick... , Franklin	I-182 starts at I-82/US 12 U.S. Route 12 in Washington U.S. Route 12 is a major east-west U.S. Highway, running from Aberdeen, Washington, to Detroit, Michigan. It spans across the state of Washington, and is the only numbered highway to span the entire state from west to east, starting near the Pacific Ocean, and crossing the Idaho state line near...  near the Tri-Cities Tri-Cities, Washington The Tri-Cities is a mid-sized metropolitan area in the southeastern part of the U.S. state of Washington, consisting of three neighboring cities: Kennewick, Pasco, and Richland. The cities are located at the confluence of the Yakima, Snake, and Columbia rivers in the semi-arid region of...  before joining US 12 and going east to Pasco Pasco, Washington Pasco is a city in and the county seat of Franklin County, Washington, United States.Pasco is one of three cities that make up the Tri-Cities region of the state of Washington... , where the freeway ends at the US 395 U.S. Route 395 in Washington In the U.S. state of Washington, U.S. Route 395 is a major state highway in two parts, separated by a long overlap with Interstate 90 between Ritzville and Spokane. The southern piece, from I-82 near the Tri-Cities to I-90 near Ritzville, is a high-speed four-lane divided highway... /US 12 interchange.