Alaskan Way Viaduct, Former elevated highway in downtown Seattle, United States

The Alaskan Way Viaduct was a double-deck concrete elevated highway that ran 2.2 miles (3.5 km) along the bay, connecting the southern neighborhoods to the northern downtown area. The upper deck carried northbound traffic while the lower deck served southbound vehicles, both running parallel to the waterfront and spanning above part of the city center.

Built in three phases from 1949 to 1959, the viaduct opened its first section on April 4, 1953, following former railroad lines along the waterfront. The 2001 Nisqually earthquake caused only minor damage, but inspections found the structure vulnerable to collapse in a major quake. A deep-bored tunnel was chosen in 2009; the viaduct closed permanently on January 11, 2019, and the new tunnel opened on February 4.

The viaduct took its name from Alaskan Way, the surface street it ran above from S. Nevada Street to the Battery Street Tunnel. Its route followed earlier railroad lines along the waterfront. The structure was a double-decker freeway with northbound traffic on the upper deck and southbound on the lower, supported by 400 columns spaced about every 51 feet.

The elevated roadway has been closed since 2019, with all traffic now moving through the new tunnel below downtown. New public space is gradually opening along the former route, providing direct access to the waterfront area that was previously cut off.

Demolition crews recycled 240 million pounds (109 million kg) of concrete and 15 million pounds (6.8 million kg) of steel rebar during removal. Most materials were reused in other regional construction projects rather than sent to landfills.