Though proposals for a rapid transit tunnel under 3rd Avenue were introduced in the 1910s and 1920s, planning for the modern bus and rail Metro Bus Tunnel only began in 1974. The King County Metro Council approved the bus tunnel proposal in November 1983, but construction did not begin until March 1987. The tunnel between Convention Place and Westlake stations was built using the cut-and-cover method, closing Pine Street for 19 months and disrupting access to the retail core. The segment from Westlake to the International District was bored with two tunnel-boring machines, heading north from Union Station and finishing within a month of each other. Tests of normal buses and the Breda dual-mode buses built specifically for tunnel routes began in March 1989; tunnel construction was declared complete in June 1990, at a cost of $469 million. Light rail tracks were installed in anticipation of future rapid transit service through the tunnel, which was later found to be poorly insulated and unusable for Link light rail. Soft openings and public previews of the five tunnel stations were held from August 1989 to September 1990, with regular bus service beginning on September 15, carrying 28,000 daily passengers in its first year of operation. For the next several years, until June 2004, service in the tunnel was provided exclusively by dual-mode buses, which ran as trolleybuses in the tunnellike the city's extensive trolleybus systemand as diesel buses on surface streets and freeways.