SR 99 tunnel construction is starting north of downtown. Are you ready? SR 99 Tunnel Project Crews working for the Washington State Department of Transportation have started construction for the SR 99 tunnel - the replacement for the Alaskan Way Viaduct. The tunnel route starts near the stadiums and ends near Aurora Avenue North and Harrison Street. The shaded section shows the future location of the SR 99 tunnel’s north entrance. Tunnel construction in this area will soon join Mercer Street, Gates Foundation and other projects already underway in the neighborhood. Excavation will begin at this site in summer 2012. Tunnel boring begins beneath downtown in mid-2013, with the tunnel scheduled to open in late 2015. SR 99/Aurora Avenue N. Harrison Street Mercer Street N Broad Street SR 99 tunnel north portal site Gates Foundation construction