The Downtown Seattle Transit Tunnel (DSTT), also referred to as the Metro Bus Tunnel, is a 1.3-mile-long (2.1 km) pair of public transit tunnels in Seattle, Washington, United States. The double-track tunnel and its four stations serve Link light rail trains on Line 1 as it travels through Downtown Seattle. It runs west under Pine Street from 9th Avenue to 3rd Avenue, and south under 3rd Avenue to South Jackson Street. Line 1 trains continue north from the tunnel to Northgate station and south through the Rainier Valley past Seattle–Tacoma International Airport to Angle Lake station as part of Sound Transit's light rail network.