I-405 and SR 18 which also allow single-passenger vehicles to use them for a variable fee, also known as HOT lanes. SR 99/SR 599 SR 99/SR 599, parts of which are also known as West Marginal Way, begins in Tukwila at I-5 and continues north to the First Avenue South Bridge, where it interchanges with SR 509, then continues as a surface street (East Marginal Way) for a few miles, then, adjacent to CenturyLink Field, becomes the SR 99 Tunnel. This tunnel passes under downtown Seattle and emerges in South Lake Union as Aurora Avenue, a divided expressway (partial control of access with interchanges) until Green Lake, where it becomes a surface street again. SR 599 was built in 1968, the freeway portion of SR 99 was built in 1956 as was the First Avenue South Bridge (a second structure was built next to the first in the early 1990s), and the Alaskan Way Viaduct was open in 1952, with an extension open in 1959, until its closure and demolition in 2019. North of that, Aurora Avenue was built in 1932, including the cantilever/truss George Washington Memorial Bridge. West Seattle Freeway The West Seattle Freeway begins in Seattle at I-5 and continues west, where it interchanges with SR 99 and terminates at a signal at Fauntleroy Way SW and 35th Avenue SW. The West Seattle Freeway was built in 1941, and the high-level bridge opened in 1984 and the roadway was widened in 2012 between I-5 and SR 99. Other freeways Most of the other freeways in the Seattle area are two lanes in each direction and generally travel in a north–south direction, with the exceptions of US 2, SR 410, SR 512, SR 518, SR 526, and Waaga Way. SR 16 is signed east–west but it travels mostly north–south. Mass transit Two public transportation agencies serve the city of Seattle: King County Metro Transit and Sound Transit. Snohomish County's Community Transit also runs bus routes to Downtown Seattle and the University of Washington. Sound Transit is the regional transit authority, commissioned by voters in 1996 to build a system of light rail, express buses, and commuter rail within the Central Puget Sound area. The agency provides a number of regional express bus routes connecting Seattle with neighboring suburbs and cities. Metro Transit's system includes a network of trolleybus routes The Sounder commuter rail system consists of two lines, linking