Washington Road Network

By | October 13, 2022

Washington state highway network.

Washington’s road network varies in density. The Cascades are a formidable obstacle to east-west traffic in the state. The road network is generally not very dense, but it is around the I-5 corridor where most major cities are located.

  • Bittranslators: State overview of Washington, including geography, economy, population and history as well as introduction to major cities of Washington.

Road management

The state highway authority is the Washington State Department of Transportation, abbreviated WSDOT. WSDOT operates approximately 29,000 lane miles and more than 3,600 bridges in the state. WSDOT also operates the largest network of ferry services in the United States.

WSDOT has its origins in the Washington State Highways Department that was founded in 1905. In that year a plan for 12 state roads was developed. The construction of roads in the management of the state began at the end of the First World War. In 1921, the Washington State Department of Public Works was established, which took over the task of developing the highway network. The first fuel tax was also introduced to pay for the road network. Shortly thereafter, in 1923, the State Highways Department became a stand-alone ministry and began developing a network of paved state highways. In 1964 it was renamed to the Washington Department of Transportation, the state was one of the first to use this name.

WSDOT is known for implementing new technologies from abroad, such as roundabouts. It was also the first state to introduce traffic signaling on a scale larger than lane signaling in tunnels and on bridges.

The Washington State Ferries consist of 10 routes and 22 ferries that are considered part of the state highway network. Most ferry services connect land and islands in the Puget Sound region, including to the isolated San Juan Islands archipelago. In addition, there are various ferry services under private management.

  • Deluxesurveillance: Nickname of Washington as The Evergreen State. Also covers geography, history, economy, politics and administration of the state.

Interstate Highways

I-5 at Seattle.

A small number of Interstate Highways traverse Washington. Interstate 5 is the state ‘s primary north-south route, from Vancouver via Olympia and Seattle to the border with Canada. This is also the primary border crossing between the United States and Canada in the Pacific Northwest. I-5 is also the main highway of the Seattle area. Interstate 82 runs in the southeast of the state, from Ellensburg through Yakima and the Tri-Cities to the Oregon border. This is part of the route from Seattle to Salt Lake City. Interstate 90 is the state ‘s primary east-west route, starting in Seattle and running through the Cascades to Spokane and on to Idaho.

There are also some auxiliary routes. Interstate 182 spurts from I -82 to the Tri-Cities (Richland, Kennewick & Pasco) and Interstate 205 is the northern portion of the Portland, Oregon bypass. Interstate 405 forms Seattle’s bypass, but is often chronically congested, so it doesn’t really function as a through-traffic bypass. Interstate 705 forms a short spur in Tacoma.

US Highways

The remaining routes are mainly single-lane highways, such as the US Highways, of which US 101 along the west coast is a major tourist route. US 2 provides a secondary link between Seattle and Spokane and is not a through route. US 395 is a major north-south route in the east of the state. US 12 is an east-west connection in the south of the state without much through importance. US 97 runs north-south through the central part of the state.

State Highways

In the northwestern state of Washington one speaks of a ‘state highway’ and the number is often written as WA-xxx. All state highways, US Highways and Interstate Highways are numbered in one system. In the case of US Highways and Interstate Highways, these have a corresponding state highway number that is not signposted, for example the SR-5 for the I-5. The system is numbered in a grid where east-west routes have even numbers and north-south routes have odd numbers. The three digit numbers are often branching off or are in the range of the one and two digit numbers. This is why the Seattle area has so many state routes in the Series 500. In Washington state routes can also be operated as freeway, this is mainly the case in the Seattle area, where there are many short freeways with a state route number in the 500 series.

From 1893, roads were already assigned as state highways, but were not given a number yet. This mainly involved roads in the less populated parts of Washington, where there were no counties and cities responsible for construction. Beginning in 1905, 12 state highways were awarded funding for construction, including 6 east-west routes through the Cascades. In 1913 a system of state highways was established with primary and secondary roads. They only had a name then and no number yet. From 1923, numbers were assigned to the primary roads that appeared on signposts shortly afterwards. In 1937 the system was reclassified and the secondary roads were also built and maintained by the state. In 1964 the system was renumbered again to the current numbering system.

Toll roads

The express lane of I-405.

There are some toll roads and express lanes in and around Seattle. Most are fully electronic, with no physical toll booths. One can use the Good To Go! use a transponder, or the more expensive license plate toll. The toll roads are under the control of WSDOT.


Road management was originally a task of the counties and cities, which saw little importance in this until the early 20th century. Transport was mostly by rail or by ship across the Columbia River. In 1905, two agencies were established, the Washington State Highway Board and the Washington State Highways Department. A law was passed that provided $110,000 ($3 million in 2016) for road development in Washington. A plan was drawn up for 12 state roads. Highway districts were created in 1918, starting the development of the road network.

In 1915 only parts of roads were ‘improved’, which often amounted to a gravel road. The vast majority of roads, including between regions, were unimproved dirt roads. In winter, the west was isolated from the east by the excessive snowfall in the Cascades, where snow often accumulates more than 2 meters deep. In 1921, the State Highway Board was replaced by the Highway Committee and the Washington State Highways Department became a division within the Washington State Department of Public Works. The first fuel tax was also introduced in 1921. However, in 1923 the State Highways Department became a separate ministry in Washington.

In 1926, the US Highways were introduced in Washington, 11 routes in all. This made it clear which roads were given priority to be asphalted. By far the highest priority was the US 99 (later I-5) from Vancouver via Olympia and Seattle to the border with Canada, which had already been completely paved in 1931. This was the only long tarmac road in the state at the time. However, approach roads around Seattle and Spokane were paved for some distance from the city. In addition, many other roads were provided with an oil layer to make them more comfortable and dust-free, the so-called ‘oiled road’. US 10 (later I-90) was given the highest priority as a connection between western and eastern Washington.

Later in the 1930s, the first major bridges were built. In 1940, the Lacey V. Murrow Memorial Bridge, a Seattle floating bridge over Lake Washington, opened. This would later become part of I-90. Also in 1940, the first Tacoma Narrows Bridge opened, collapsing in a storm shortly after opening. The Tacoma Narrows Bridge was the third longest suspension bridge in the world at the time. The road network was also significantly improved at the end of the 1930s, especially the coverage ratio of asphalted roads rose sharply. By 1940, nearly all US Highways were paved, including three east-west routes through the Cascades, as well as the Columbia River road, although traditionally US 30 in Oregon the main route was along the river. In the late 1930s, the first longer stretches of road had 2×2 lanes, the most important being US 99 / State Route 1 from Olympia via Tacoma and Seattle to Everett. State Route 2 / US 10 east of Spokane also had 2×2 lanes.

In 1956, the Interstate Highways system was established by President Eisenhower. Originally, two routes were planned in Washington, I-5 and I-90. Later, I-82 was added. These would replace two major US Highways, I-5 would replace US 99 and I-90 would replace US 10. Construction of the Interstate Highways began primarily in the early 1960s, but it was not until the mid-1970s that large sections of the highways were completed. In 1964, the Highways Department was transformed into the current Washington Department of Transportation, and the network of state highways was renumbered that year.

In 1972, the North Cascades Highway (SR-20) was completed as an all-new east-west link through the Cascades in the north of the state. The first HOV lanes in the state also opened in 1972, on State Route 520. A dense network of freeways was built in the Seattle area, mainly short links between the two north-south routes through the metropolitan area. In 1979, the Hood Canal Bridge was destroyed in a storm. In 1980, the Mount St. Helens volcano erupted, destroying many local roads in the area. In 1990 the Lacey V. Murrow Memorial Bridge sank during regular maintenance because the basins were full of water. In 1991, a second, smaller renumbering of the state routes followed. In 2001, the Nisqually earthquake, a magnitude 6.8 earthquake, occurred southwest of Seattle. This made it clear that the road network was vulnerable, and since then a lot of money has been invested in making infrastructure earthquake-proof. One of its largest projects is the replacement of the Alaskan Way Viaduct in Seattle with a drilling tunnel. However, the construction was plagued by setbacks and delays.

Washington Road Network