and Sunday operation was introduced in May 2009. Simulated light rail testing in the tunnel also began on May 20, 2009, with two-car trains operating alongside in-service buses, making it the first joint bus and rail tunnel with stations in the United States; the Mount Washington Transit Tunnel, a joint bus and rail tunnel in Pittsburgh, Pennsylvania, had already been in operation but lacked underground stations. Service on the Central Link light rail line began on July 18, 2009, operating from Westlake station in the tunnel to Tukwila International Boulevard station near the airport. Light rail service was extended north from Westlake to University of Washington station (via Capitol Hill station) on March 19, 2016, coinciding with the moving of several bus routes out of the tunnel to accommodate increased train frequencies. The ramp from International District/Chinatown station to the Interstate 90 express lanes was closed in September 2018 as part of preparations for East Link construction. End of bus service In November 2015, King County Metro signed a $147 million agreement to sell Convention Place station to the Washington State Convention Center for redevelopment. The convention center plans to build a new expansion on the property, necessitating the closure of the station and transit tunnel to buses earlier than planned. In 2017, Sound Transit and the Seattle Department of Transportation announced that the tunnel would become rail-only in 2019, two years sooner than the planned switch in 2021 to coincide with the opening of the Northgate Link Extension. Convention Place station was permanently closed on July 21, 2018, and was replaced with a set of bus stops on 9th Avenue and a new tunnel access ramp. Bus service in the tunnel ended on March 23, 2019, with a ceremonial trip by a preserved Breda dual-mode bus at 1 a.m. The remaining 830 bus trips through the tunnel, serving approximately 37,000 riders on seven routes, were redirected onto surface corridors on 2nd, 3rd, 4th, 5th, and 6th avenues. Metro and the city government also increased surface street capacity for buses by introducing all-door boarding for all 3rd Avenue and Westlake Avenue routes at 31 stops, improving signal timing, and adding a new northbound bus lane on 5th and 6th avenues. During early 2020, Sound Transit built connections to East Link at International District/Chinatown station. Over a ten-week period that began in January 2020, four-car trains ran on a single track