The freeway intersects Des Moines Memorial Drive and 154th Street north of Seattle–Tacoma International Airport and continues east into SeaTac.

[5][6] The freeway follows the Central Link light rail line into Tukwila and intersects 51st Avenue before an interchange with I-5.

[7][8] 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.

[12][13][14] 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.

[25] 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.