Interstate 90 (I-90), designated as the American Veterans Memorial Highway, is a transcontinental Interstate Highway that runs from Seattle, Washington, to Boston, Massachusetts. It crosses Washington state from west to east, traveling from Seattle across the Cascade Mountains and into Eastern Washington, reaching the Idaho state line east of Spokane. I-90 intersects several of the state's other major highways, including I-5 in Seattle, I-82 and U.S. Route 97 (US 97) near Ellensburg, and US 395 and US 2 in Spokane.
I-90 is the only Interstate to cross the state from west to east, and the only one to connect the state's two largest cities, Seattle and Spokane. It incorporates two of the longest floating bridges in the world, the Lacey V. Murrow Memorial Bridge and the Homer M. Hadley Memorial Bridge, which cross Lake Washington from Seattle to Mercer Island. I-90 crosses the Cascades at Snoqualmie Pass, one of the busiest mountain pass highways in the United States, and uses a series of viaducts and structures to navigate the terrain. The freeway travels across suburban bedroom communities in the Seattle metropolitan area, the forests of the Cascade Range, and the high plains of the Columbia Plateau.
The crossing at Snoqualmie Pass was established as a wagon road in 1867 and incorporated into a cross-state auto trail, known as the Sunset Highway, in the early 1910s. The Sunset Highway was incorporated into the national highway system in 1926 as part of US 10, which I-90 replaced when it was designated in 1957. The first segments of the freeway, located in Spokane and Spokane Valley, opened at around the same time and the state government completed upgrades of US 10 to Interstate standards for most of the route by the late 1970s.
The section of I-90 between Seattle and I-405 in Bellevue was delayed for decades because of environmental concerns and lawsuits by local groups over the freeway's potential impact on nearby neighborhoods. A compromise agreement was reached by the federal, state, and local governments in 1976 to build a second floating bridge across Lake Washington and include extensive parks above tunneled sections of I-90, which were completed in the late 1980s and early 1990s. The new floating bridge opened in 1989 and carried bi-directional traffic while the original floating bridge was renovated. The old bridge's center pontoons sank during a November 1990 windstorm due to a contractor error and were rebuilt over the following three years, reopening to traffic on September 12, 1993, marking the completion of the transcontinental highway.
Route description
Interstate 90 is the longest freeway in Washington state, at nearly in length, and is the only Interstate to traverse the state from west to east across the Cascade Mountains., with inset maps. It is listed as part of the National Highway System, classifying important to the national economy, defense, and mobility, and the state's Highway of Statewide Significance program, recognizing its connection to major communities. The Washington State Legislature designated the highway as the "American Veterans Memorial Highway" in 1991 to honor U.S. soldiers. A section of I-90 between Seattle and Thorp named the Mountains to Sound Greenway was designated in 1998 as a National Scenic Byway, in recognition of its scenic views.
I-90 is maintained by the Washington State Department of Transportation (WSDOT), who conduct an annual survey of traffic volume that is expressed in terms of annual average daily traffic (AADT), a measure of traffic volume for any average day of the year. A section of I-90 in Bellevue's Eastgate neighborhood carries a daily average of 150,000 vehicles, making it the highway's busiest. The highway's least busy section, near SR 21 west of Ritzville, carried 11,000 vehicles in 2016. The freeway has a maximum speed limit of in urban areas, in mountainous areas, and in rural areas. Several proposals to raise the speed limit of the rural section between Vantage and Spokane to have been submitted and denied by the state government due to safety concerns.
Seattle, Mercer Island, and Bellevue
I-90 begins its eastward journey at the intersection of Edgar Martinez Drive South (part of SR 519) and 4th Avenue South in the SoDo neighborhood south of Downtown Seattle. The interchange is adjacent to T-Mobile Park, home to the Seattle Mariners baseball team, and includes a pair of ramps to SR 519 and an additional offramp to 4th Avenue South north of Royal Brougham Way and near Lumen Field. The ramps converge over the Stadium light rail station adjacent to King County Metro's bus bases and were formerly joined by bus-only express lane ramps from the Downtown Seattle Transit Tunnel and 5th Avenue in the International District. I-90 travels east through a major interchange with I-5 at the northwest corner of Beacon Hill and passes under the Jose Rizal Bridge.
The freeway wraps around the north end of Beacon Hill and intersects Rainier Avenue at the site of the Judkins Park light rail station, joined by a multi-use bicycle and pedestrian trail that forms part of the Mountains to Sound Greenway. I-90 travels east into the Mount Baker Tunnel, a set of tunnels which run under Sam Smith Park and the Mount Baker Ridge neighborhood to Lake Washington; they are also listed on the National Register of Historic Places. At the east end of the tunnels, traffic continues onto a pair of floating bridges; the eastbound lanes are carried by the Lacey V. Murrow Memorial Bridge, while the westbound lanes, multi-use trail, and light rail tracks are carried by the wider Homer M. Hadley Memorial Bridge. The two floating bridges connect Seattle to the Eastside suburbs and are among the longest in the world, at and in length, respectively.
From the east end of the bridge, I-90 continues onto Mercer Island and travels under the Mercer Island Lid, a landscaped park built atop a curved section of the freeway between West Mercer Way and 76th Avenue Northeast. I-90 emerges in downtown Mercer Island, adjacent to its light rail station in the freeway median and park and ride. The freeway passes under a smaller lid at Luther Burbank Park and leaves the island on the East Channel Bridge, which crosses a smaller arm of Lake Washington into Bellevue. I-90 travels to the south of Enatai and Beaux Arts Village and intersects Bellevue Way, where light rail tracks turn north away from the freeway, before crossing the Mercer Slough and its wetlands. The freeway gains a set of collector–distributor lanes and widens to 16 lanes as it passes under a disused railroad bridge that is slated to be part of the Eastside Rail Corridor trail. The freeway then meets I-405 in a large stack interchange northwest of the Factoria Mall and near the headquarters of T-Mobile US. South of the Bellevue College campus in Eastgate, I-90 intersects 142nd Place Southeast using direct ramps from its high-occupancy vehicle (HOV) lanes. Near the former Bellevue Airfield, I-90 turns southeast to run downhill from Cougar Mountain and along the shore of Lake Sammamish towards Issaquah.
East King, Snoqualmie Pass, and Kittitas
At the south end of Lake Sammamish and northwest of downtown Issaquah, I-90 passes through Lake Sammamish State Park and intersects SR 900. The freeway travels along the north edge of downtown Issaquah, zig-zagging to the south and north to avoid the ridge of Issaquah Highlands and western Tiger Mountain. I-90 leaves Issaquah and enters the heavily forested Issaquah Alps, skirting the north edge of the Tiger Mountain State Forest as it passes Preston. Northeast of Tiger Mountain, the freeway intersects SR 18 and an arterial street connecting to Snoqualmie and Snoqualmie Ridge. I-90 continues southeast past the Snoqualmie Casino to North Bend, where it intersects SR 202. The freeway travels around the southern edge of North Bend and neighboring Tanner in the foothills of Rattlesnake Ridge. I-90 continues southeasterly along the South Fork of the Snoqualmie River into the Snoqualmie National Forest, which also hosts several state parks and campgrounds.
I-90 continues in a southern arc around several mountains in the Alpine Lakes Wilderness while following the South Fork of the Snoqualmie River. At the east end of the arc near the Asahel Curtis Picnic Area, the freeway's westbound and eastbound lanes are split by a wide median that includes the Denny Creek Campground. I-90 continues northeast on two high viaducts and ascends to Snoqualmie Pass, the lowest of the state's three major Cascades passes at an elevation of . The pass handles 28,000 vehicles (including 6,500 trucks) on an average weekday, making it one of the busiest mountain highways in the United States. I-90 intersects the Pacific Crest Trail and SR 906 at the pass, providing access to the adjacent Snoqualmie ski resort. The freeway travels south into Kittitas County and intersects SR 906 Spur at Hyak. I-90 continues south through the Wenatchee National Forest along the eastern shore of Keechelus Lake, under steep cliffs that were cut using controlled blasting. At the south end of the lake, the freeway passes under a arched wildlife bridge, which is the first to be built in Washington state.
While Snoqualmie Pass does not have an annual closure like other passes in the Cascades, it does suffer from vehicle restrictions and occasional days-long shutdowns during the wintertime for avalanche control and clearing collisions. I-90 has several chain-on and chain-off areas on the highway shoulders between North Bend and Cle Elum, including variable-message signage to inform drivers of road conditions. WSDOT estimates that it costs $2–3 million annually to keep Snoqualmie Pass open in the wintertime, which sees an average snowfall of and about 120 hours of closures per year.
I-90 continues southeast along the Yakima River to Easton, where it leaves the national forest and is joined by the Palouse to Cascades State Park Trail, part of Iron Horse State Park. The freeway passes several ranches and resort communities, including Suncadia, before reaching Cle Elum. I-90 runs to the south of downtown along the Yakima River and intersects SR 10 east of the city before crossing the river. SR 10 follows the former route of US 10 on the north side of the Yakima River, connecting to SR 903 and SR 970. The two highways continue southeast along the Yakima River and enter the Kittitas Valley near Thorp. I-90 begins a concurrency with US 97 west of Ellensburg, which continues as the freeway travels around the outskirts of the city to an interchange with I-82, which travels south with US 97 along the Yakima River towards Yakima.
Columbia Plateau and Spokane area
I-90 crosses into the Columbia Plateau at the east end of the Kittitas Valley, traveling due east past Olmstead Place State Park and the town of Kittitas. The freeway travels across a series of hills while following the Ryegrass Coulee, including a rest area at Ryegrass Hill near the Wild Horse Wind Farm. I-90 then reaches Vantage, where it travels past the Ginkgo Petrified Forest State Park, one of the largest collections of petrified trees in the world, before crossing the Columbia River on the Vantage Bridge. The bridge ascends up to the cliffs on the western shore of Grant County, where I-90 intersects SR 26 and turns north along the Babcock Bench. The freeway then passes several scenic viewpoints for Lake Wanapum and the Wild Horse Monument, a piece of public art placed atop a hill to the east.