Washington State Route 518

State Route 518 (SR 518) is a 3.42-mile-long (5.50 km) state highway located entirely within King County in the U.S. state of Washington. The freeway begins in Burien at an interchange with SR 509 and travels east to serve Seattle–Tacoma International Airport and intersect SR 99 in SeaTac. SR 518 continues east into Tukwila and ends at an interchange with Interstate 5 (I-5), as the freeway becomes I-405. The highway was codified in 1937 as the western segment of Secondary State Highway 1L (SSH 1L) and designated as SR 518 during the 1964 highway renumbering. During the 1970s, the roadway was widened into a freeway to serve the airport and serves over 100,000 vehicles per day.

State Route 518
SR 518 is highlighted in red
Route information
Auxiliary route of I-5
Defined by RCW 47.17.715
Maintained by WSDOT
Length3.42 mi[1] (5.50 km)
Existed1964[2]–present
Major junctions
West end SR 509 in Burien
  SR 99 in Seatac
East end I-5 / I-405 in Tukwila
Location
CountiesKing
Highway system
← SR 516SR 519 →

Route description
SR 518 eastbound approaching its interchange with I-5 and I-405 in Tukwila.

SR 518 begins at a partial cloverleaf interchange with SR 509 east of Burien and travels east as a divided freeway,[3] passing north of Highline High School.[4] The freeway intersects Des Moines Memorial Drive and 154th Street north of Seattle–Tacoma International Airport and continues east into SeaTac.[5][6][7] SR 518 intersects the Airport Expressway and International Boulevard, signed as SR 99, south of the Tukwila International Boulevard station.[8][9] The freeway follows the Central Link light rail line into Tukwila and intersects 51st Avenue before an interchange with I-5.[10][11][12] At the interchange, located northwest of the Westfield Southcenter Mall, the Central Link turns north along I-5 and SR 518 ends as the roadway continues east as I-405 towards Renton.[13][14]

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 average annual daily traffic (AADT), which is a measure of traffic volume for any average day of the year. In 2011, WSDOT calculated that between 38,000 and 102,000 vehicles per day used the highway, mostly between Seattle–Tacoma International Airport and I-5.[15] SR 518 are designated as part of the National Highway System and as a Highway of Statewide Significance for serving Seattle–Tacoma International Airport.[16][17][18]

History
Southbound I-5 at its interchange with I-405 and SR 518 in Tukwila.

A highway between Burien and Tukwila has existed since the 1890s and was first codified in 1937 as a segment of SSH 1L, which extended from PSH 5 in Renton west to intersect PSH 1 and US 99 in Tukwila and end at SSH 1K south of Sunnydale, later renamed Burien.[19][20] The section between PSH 5 in Renton and PSH 1 in Tukwila was removed in 1957 after the construction of the Seattle–Tacoma International Airport, located on PSH 1 and US 99.[21][22] The remaining highway was later re-designated as SR 518 during the 1964 highway renumbering,[23] being codified as such in 1970.[2][24] The western terminus of SR 518, an interchange with SR 509, was opened to traffic in November 1968,[25] while the Airport Expressway was opened in 1970 and widened in the 1990s by the Port of Seattle.[26][27] The freeway segment between SR 99 and I-5 was built in the 1970s. No major revisions to the route of SR 518 have occurred since the 1990s,[28] however SR 99 from SR 518 to SR 599 was removed to the highway system in 2003.[29]

Beginning in 2005, an elevated light rail guideway was constructed on the north side of SR 518, for Sound Transit's Central Link line serving Downtown Seattle, the Rainier Valley and Sea-Tac Airport. The construction led to nighttime closures of the highway and other interruptions until construction finished in 2007.[30] Tukwila International Boulevard station was built to the north of SR 518 at its interchange with SR 99 (International Boulevard) near Sea-Tac Airport.[31]

Exit list

The entire highway is in King County.

Locationmi[1]kmDestinationsNotes
Burien0.00–
0.32		0.00–
0.51		 SR 509 – Des Moines, SeattleWestern terminus, continues as 148th Street
0.831.34Des Moines Memorial DriveWestbound exit and eastbound entrance
SeaTac0.83–
1.39		1.34–
2.24		 To SR 99 / South 154th StreetEastbound exit and westbound entrance
1.62–
2.31		2.61–
3.72		Sea-Tac Airport
2.36–
2.52		3.80–
4.06		 SR 99Westbound exit and eastbound entrance
Tukwila2.69–
2.94		4.33–
4.73		51st Avenue South, Southcenter ParkwayEastbound exit and westbound entrance
3.01–
3.42		4.84–
5.50		 I-5 / I-405 – Seattle, Renton, Tacoma, PortlandEastern terminus, continues as I-405; I-5 north exit 154, south exits 154A-B
1.000 mi = 1.609 km; 1.000 km = 0.621 mi
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gollark: Sure. I'll probably just buy a few as I actually need them.

References
  1. Staff (2012), State Highway Log: Planning Report 2011, SR 2 to SR 971 (PDF), Washington State Department of Transportation, pp. 1592–1594, retrieved January 30, 2013
  2. "47.17.715: State route No. 518", Revised Code of Washington, Washington State Legislature, 1970, retrieved January 30, 2013
  3. SR 509: Junction SR 518/S 146th St (PDF), Washington State Department of Transportation, August 1, 2011, retrieved January 30, 2013
  4. "Feature Detail Report for: Highline High School", Geographic Names Information System, United States Geological Survey, September 10, 1979, retrieved January 30, 2013
  5. SR 518: Junction Des Moines Way S (PDF), Washington State Department of Transportation, August 15, 2006, retrieved January 30, 2013
  6. "Feature Detail Report for: Seattle-Tacoma International Airport", Geographic Names Information System, United States Geological Survey, March 1, 1990, retrieved January 30, 2013
  7. "Feature Detail Report for: SeaTac", Geographic Names Information System, United States Geological Survey, June 1, 1990, retrieved January 30, 2013
  8. SR 518: Junction S 154th St (PDF), Washington State Department of Transportation, May 10, 2010, retrieved January 30, 2013
  9. SR 518: Junction SR 99 (PDF), Washington State Department of Transportation, May 10, 2010, retrieved January 30, 2013
  10. "Feature Detail Report for: Tukwila", Geographic Names Information System, United States Geological Survey, September 10, 1979, retrieved January 30, 2013
  11. SR 518: Junction 51st Ave S (PDF), Washington State Department of Transportation, May 6, 2010, retrieved January 30, 2013
  12. SR 5 - Exit 154: Junction SR 405/SR 518 (PDF), Washington State Department of Transportation, January 5, 2009, retrieved January 30, 2013
  13. Google (January 30, 2013). "State Route 518" (Map). Google Maps. Google. Retrieved January 30, 2013.
  14. Staff (2011), 2011 Annual Traffic Report (PDF), Washington State Department of Transportation, p. 195, retrieved January 30, 2013
  15. National Highway System: Seattle, WA (PDF) (Map). Federal Highway Administration. October 1, 2012. Retrieved January 30, 2013.
  16. Transportation Commission List of Highways of Statewide Significance (PDF), Washington State Transportation Commission, July 26, 2009, retrieved January 30, 2013
  17. Puget Sound Region: Highways Of Statewide Significance (PDF) (Map). Washington State Department of Transportation. 2009. Retrieved January 30, 2013.
  18. Washington: Tacoma Quadrangle (JPG) (Map). 1:125,000. United States Geological Survey. March 1900. Retrieved January 30, 2013.
  19. Washington State Legislature (March 18, 1937), "Chapter 207: Classification Public Highways", Session Laws of the State of Washington, Session Laws of the State of Washington (1937 ed.), Olympia, Washington: Washington State Legislature, p. 996, retrieved January 30, 2013, (l) Secondary State Highway No. 1L; beginning at a junction with Primary State Highway No. 5 in the vicinity south of Renton, thence in a westerly direction by the most feasible route to a junction with Primary State Highway No. 1, thence in a westerly direction by the most feasible route to a junction with Secondary State Highway No. 1K near Sunnydale.
  20. Washington State Legislature (1957), "Chapter 172", Session Laws of the State of Washington, Session Laws of the State of Washington (1957 ed.), Olympia, Washington: Washington State Legislature, p. 632, retrieved January 30, 2013
  21. Seattle, 1958 (JPG) (Map). 1:250,000. United States Geological Survey. 1958. Retrieved January 30, 2013.
  22. Prahl, C. G. (December 1, 1965), Identification of State Highways (PDF), Washington State Highway Commission, Department of Highways, retrieved January 30, 2013
  23. Seattle, 1965 (JPG) (Map). 1:250,000. United States Geological Survey. 1965. Retrieved January 30, 2013.
  24. "Slide Blocks Two Lanes of Freeway", The Spokesman-Review, Spokane, Washington, p. 3, December 25, 1968, retrieved January 30, 2013
  25. Port of Seattle Centennial: The 1970s, Port of Seattle, retrieved January 30, 2013
  26. "New thoroughfare proposed for Sea-Tac", Moscow-Pullman Daily News, Moscow, Idaho, p. 11, December 27, 1990, retrieved January 30, 2013
  27. Washington State Highways, 2011–2012 (PDF) (Map). 1:842,000. Washington State Department of Transportation. 2011. Retrieved January 30, 2013.
  28. Washington State Legislature (January 23, 2003), "Senate Bill 5376: An Act Relating to the alignment of state route number 99", Session Laws of the State of Washington, Session Laws of the State of Washington (1937 ed.), Olympia, Washington: Washington State Legislature
  29. "Sound Transit completes construction of elevated light rail trackway between Seattle and Tukwila" (Press release). Sound Transit. September 27, 2007. Retrieved August 22, 2016.
  30. Hubbard, Ian (July 16, 2009). "The long bridge to Tukwila". Seattle Daily Journal of Commerce. Retrieved August 22, 2016.

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