Seattle, Washington

According to, Seattle is a city in the United States, in the state of Washington. It is a port city with 734,000 inhabitants and an urban area with 4,012,000 inhabitants (2021). It is the largest city in the state, but not the capital, which is Olympia.


The Interstate 90 Floating Bridges over Lake Washington.

According to, the conurbation is located on the Puget Sound, an inlet of the Pacific Ocean. Also in the metropolitan area is the larger Lake Washington, which separates Seattle from the eastern suburbs. The eastern suburbs border the Cascade Mountains, and Mount Rainier is visible from almost the entire metropolitan area on clear days. Large parts of the suburban area are hilly. The agglomeration measures approximately 100 kilometers from north to south and 25 kilometers from east to west, so it is elongated. In fact, the agglomeration consists of 3 large centers with their own suburbs, which have grown together over time. These centers are Seattle, Bellevue, and Tacoma. Some distance away is Washington’s capital Olympia, southwest of Seattle, at the southernmost tip of the Puget Sound.


Seattle is located in slightly hilly terrain, surrounded by higher mountains of the Cascades. There are minor height differences throughout the conurbation, with the highest peaks around the suburb of Issaquah. The 4,392 meter high Mount Rainier is visible from large parts of the metropolitan area. The region has a lot of afforestation, especially the expensive eastern suburbs are located in wooded areas. The islands in the region also have a lot of afforestation.

Seattle’s climate is a temperate oceanic climate, and the city has an unfair reputation for being rainy. Summers are usually dry, but clouds are often present.


The metropolitan area is a major industrial center in the United States, with a long industrial valley running from the south side of downtown to suburbs like Tukwila, Renton, Kent, and Auburn. In addition, there are large companies such as Boeing and Microsoft in the urban area. The main port activities are in Tacoma, although Seattle itself also has a port. Although Seattle has the largest business center, many suburbs also have many office parks, including Everett, Bellevue, Redmond and Tacoma. In addition, the larger suburbs also have industrial estates.

Population growth

The Ship Canal Bridge from Interstate 5.

The metropolitan area is divided into King County, which includes Seattle, Pierce County, which includes Tacoma, and Snohomish County, which contains the northern suburbs.

Year King pierce Snohomish total
1920 389.000 144,000 68,000 601,000
1930 464,000 164,000 79,000 707,000
1940 505,000 182,000 89,000 776,000
1950 733,000 276,000 112,000 1,121,000
1960 935,000 322,000 172,000 1,429,000
1970 1,157,000 411,000 265,000 1,833,000
1980 1,270,000 486,000 338,000 2,094,000
1990 1,507,000 586,000 466,000 2,559,000
2000 1,737,000 701,000 606,000 3,044,000
2010 1,931,000 795,000 713,000 3,439,000
2020 2,273,000 929,000 829,000 4,025,000
2021 2,252,000 926,000 834,000 4,011,000

The metropolitan area of Seattle was already quite a large city in the early 20th century, but it only started to grow strongly after World War II, a steady growth that has continued for decades, and there are no signs of slowing down yet. The growth is strong, but not explosive. In 2020, the agglomeration exceeded the 4 million inhabitants mark, but growth came to a halt from that point on. The conurbation will still have room to grow in the coming decades, but in the long term the Cascade Mountains will form a barrier.

Road network

Seattle’s highway network.

Most of the commuter traffic is oriented north-south. Interstate 5 is the metropolitan area’s major transit route, serving most suburbs and sub-centers from the south, with the exception of Bellevue, which is served by the Interstate 405 bypass. However, I-405 only goes around Seattle itself, and SR-167 and SR-512 form an additional bypass south of Seattle, around Tacoma. In terms of east-west traffic, Interstate 90 is a major route, connecting downtown Seattle to the suburb of Bellevue and heading inland. The SR-520 does this too, just a little further north. Both roads cross Lake Washington via floating bridges. There is no question of large-scale east-west traffic, although both bridges are bottlenecks.

The main highway network is supplemented by a number of State Routes, mainly in the 500 series. SR-16 connects relatively remote Bremerton to Tacoma, and State Route 99 parallels Interstate 5 between Tacoma and Everett, and is a major north-south route in the city of Seattle that runs through downtown. SR-18 is a major bypass for traffic from the industrial areas around Tacoma and Auburn heading east, as it eliminates I-405 and Bellevue.

List of freeways

The Alaskan Way Viaduct.

length first opening last opening max AADT 2013
116 km 196x 1969 263,000
26 km 1940 199x 160,000
49 km 1954 1968 202,000
2 km ? 1990 73,000
29 km 1963 1973 69,000
43 km 1940 ? 113,000
46 km ? ? 95,000
15 km 1953 2019 88,000
46 km 196x 197x 119,000
3 km 1972 1972 68,000
12 km 197x 1997 62,000
19 km 1972 1972 106,000
3 km ? ? 38,000
6 km ? ? 116,000
21 km 1963 1990 100,000
15 km 197x 197x 91,000
5 km 1965 1965 62,000
7 km 198x 198x 75,000
3 km 1968 1968 46,000


Seattle has traditionally been one of the major industrial centers of the western United States, especially in the south, and the southern suburbs have traditionally been heavily industrialized. However, Seattle’s growth started relatively late. Only around 1905 the limit of 100,000 inhabitants was exceeded, after which the city grew to 560,000 inhabitants in 1960, after which the population decreased for about 20 years to 495,000 inhabitants in 1980. Since then, the city has grown steadily again, to 610,000 inhabitants in 2010. The growth of the metropolitan area was stronger, although not nearly as extensive as in the major cities in California. Construction of Seattle’s highway network began in the late 1930s with the construction of bridges. In 1940, the first floating bridge between Seattle and Mercer Island was opened, which would later become I-90. Also opened in 1940, the Tacoma Narrows Bridge, which collapsed later that year and was replaced by a new bridge in 1950. From the early 1950s, a highway network was built in the city, which was accelerated from 1956 by the creation of the Interstate Highway system. In 1953, the Alaskan Way Viaduct opened in downtown Seattle. Interstate 5 was built through Seattle in the early and mid-1960s. At the same time, I-405 was immediately constructed as a bypass, at the time mainly intended to connect the eastern cities with the southern industrial cities.

During the 1970s, the last links were opened, and I-405 was widened to a more modern highway. One of the most prominent missing links was I-90 in Bellevue. It was only opened in the early 1990s. The motorway network has hardly been adapted since the late 1970s, which has resulted in a sharp increase in traffic jams, partly due to the geographical spread of the urban area, the work locations and the dependence on only a few links, which also have little capacity. Only Interstate 5 has been run at significant capacity, most other highways have 2×2 or 2×3 lanes. Construction has been underway since 2005 to widen the highways, most prominently I-405. There have also been plans for an I-605 to form Seattle’s outer ring road. So far this has not come to pass. Tacoma Narrows Bridge for traffic. In 2019, the Alaskan Way Viaduct was replaced with a tunnel.


Seattle has a number of well-known bridges and tunnels.

Toll roads

Tolls have to be paid at some points around Seattle. Toll collection is fully electronic everywhere with Good To Go!, except on the Tacoma Narrows Bridge.

  • Washington Interstate 405 (Express Lanes)
  • Washington State Route 16 (Tacoma Narrows Bridge)
  • State Route 99 in Washington (Alaskan Way Viaduct replacement tunnel)
  • Washington State Route 167 (HOT lanes)
  • Washington State Route 520 (Evergreen Point Floating Bridge)


Seattle is one of the most congested cities in the United States, in 2016 Seattle was in 4th place in the TomTom Traffic Index. [2] One problem is that the city is stretched in the north-south direction, making these routes also the most traffic-prone, especially I-5 and I-405 have notorious congestion and can therefore not be a good alternative to each other. Moreover, the highways are largely not that wide, only I-5 is a really wide highway and intensities of more than 200,000 vehicles per day are also measured here. On other highways, the intensities are lower, but fewer lanes are available.

Seattle, Washington