Seattle with Lakewood along its Southern run and Seattle with Everett along its Northern run. Several stations in intermediate cities along the lines are also served. The light rail system, called Link light rail, includes the initial from downtown Seattle to Sea-Tac Airport, which began service in 2009. Extension to the University of Washington via the University Link tunnel and Angle Lake station began service in 2016; they were followed by the Northgate Link Extension in 2021. It was named the 1 Line and will be joined by other lines in future extensions approved by voters in 2008 and 2016. Further light rail extensions are planned to connect to Lynnwood and other areas to the north; east across Lake Washington to Bellevue and Redmond; and south to Federal Way. The Sound Transit 3 ballot measure, passed in 2016, will further expand the system both regionally and within the city, with service to Tacoma, Everett, Issaquah, south Kirkland, and to the neighborhoods Ballard and West Seattle. The Downtown Seattle Transit Tunnel is a 1.3-mile tunnel under downtown built in 1987 and opened in 1990, to relieve bus congestion along surface streets. Originally served by dual-mode buses that operated electrically within it, the tunnel was retrofitted from 2005 to 2007 to accommodate light rail, and in 2009, Link light rail trains began serving tunnel stations as part of the initial Central Link segment. All tunnel bus routes were rerouted to surface streets in 2019 to make way for the demolition of Convention Place Station, making the tunnel an exclusive subway for Link trains within the city core. Above the tunnel, 3rd Avenue through downtown serves as a major bus arterial, with access restricted to buses only during peak commuting hours. The city is currently in the process of expanding a modern streetcar network. In December 2007, the city inaugurated its South Lake Union Streetcar line between Westlake Center and stops in the South Lake Union neighborhood. In 2009, the Seattle city council approved a second line, the First Hill Streetcar, to connect First Hill to Link light rail at Capitol Hill and International District/Chinatown stations. The line began service in 2016 after two years of delays. Metro Transit also operated a historic Waterfront Streetcar line that ran along Alaskan Way, but the streetcar's maintenance barn was demolished to make room for the Olympic Sculpture Park, resulting in the subsequent closure of the