AKA: State of Washington, Department of Transportation, Alaskan Way Viaduct Replacement Tunnel, Waterfront, Seattle, WA

Structure Type: built works - infrastructure - roads

Designers: Howard Needles Tammen and Bergendoff (HNTB) (firm); Seattle Tunnel Partners (firm); Ruben Bergendoff (architect); Ernest Emmanuel Howard (architect); Enoch Ray Needles (civil engineer); Henry C. Tammen (architect)

Dates: constructed 2013-2019

Waterfront, Seattle, WA


A consortium of two large construction contractors formed calling itself the "Seattle Tunnel Partners" to undertake the construction of the SR 99 Tunnel, a 9,270-foot-long, two-deck, underground roadway designed to replace the 1950s-era Alaska Way Viaduct. Construction on the tunnel began in 2013 and was largely complete by late 2018. Its official dedication occurred on 02/04/2019, about three years behind schedule due to delays with Bertha, the enormous tunnel-boring machine brought in from Japan to complete the digging work.

Building History

The 1989 collapse of the Cypress Structure, an elevated roadway in Oakland, CA, comparable to the Alaska Way Viaduct, caused State of WA Department of Transportation (DOT) engineers to reassess the safety of the Seattle elevated roadway after a large earthquake. The Cypress Structure's fall during the Loma Prieta Earthquake of 10/17/1989 chilled highway engineers up and down the West Coast, and spurred the removal of the damaged Embarcadero Freeway in San Francisco in 1990-1991.

The Nisqually Earthquake of 02/28/2001 forced WA DOT officials to redouble examination of the Alaska Way Viaduct, which found significant problems with the support of its piers in the filled soil of the waterfront.

PCAD id: 24141