International Airport, located on PSH 1 and US 99. The remaining highway was later re-designated as SR 518 during the 1964 highway renumbering, being codified as such in 1970. The western terminus of SR 518, an interchange with SR 509, was opened to traffic in November 1968, while the Airport Expressway was opened in 1970 and widened in the 1990s by the Port of Seattle. 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, however SR 99 from SR 518 to SR 599 was removed to the highway system in 2003. 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. Tukwila International Boulevard station was built to the north of SR 518 at its interchange with SR 99 (International Boulevard) near Sea-Tac Airport. Exit list References External links Highways of Washington State 518 Transportation in King County, Washington