The Downtown Seattle Transit Tunnel, also referred to as the Metro Bus Tunnel, is a 1.3-mile (2.1 km) public transit tunnel that runs the length of downtown Seattle, from 9th Avenue and Pike Street to 5th Avenue S. and S. Jackson Street. Approved by Metro Transit in 1983, construction began in 1987. It was completed and service began in 1990, at a total cost of $455 million. In May 2000, the King County Council transferred ownership to Sound Transit, but ownership was transferred back to King County Metro in 2002.
The tunnel was closed on September 24, 2005 for modification to accommodate both buses and Sound Transit's Central Link light rail trains on a shared alignment. Prior to closure, around two dozen bus routes ran through the tunnel. The buses were dual-powered, operating as trolleybuses in the tunnel using electricity from overhead wires and as diesel buses on city streets. It reopened on Monday, September 24, 2007. The two-year closure included retrofits for light rail and other operating system upgrades. A stub tunnel, branching from the main tunnel, was constructed under Pine Street between 7th and Boren Avenues to allow light rail trains to stop and reverse direction and for future extension of Central Link.
Due to the conversion to light rail, dual-mode trolleybuses can no longer operate in the tunnel. Those buses have already been replaced by Metro's current new fleet of hybrid buses, which produce fewer emissions than standard diesel buses, and, unlike the trolleybuses, require no connection to overhead wires.
Sound Transit Link Light Rail is a rapid transit project in the Greater Seattle region, originally approved by a ballot measure in November 1996. Two lines are currently operating as of 2009: Tacoma Link, which uses 3 vehicles built by Škoda, and Central Link, which uses 35 vehicles built by Kinki Sharyo. The University Link extension, extending Central Link northward from downtown Seattle to the University of Washington, began preliminary construction work in late 2008 with service slated to start in 2016. In addition, voters approved a November 2008 ballot measure to extend Link light rail north via Northgate to Lynnwood (with planning and property acquisition to support later extension to Everett), south to Redondo Heights Park & Ride in Federal Way (with route planning to support later extension to Tacoma and extensions of Tacoma Link to the east and west), and east via Mercer Island and Bellevue to Microsoft's main campus in Redmond (with route planning and right-of-way acquisition to support later extension to downtown Redmond).