SR 99 Tunnel

Alaska Way Viaduct Replacement Tunnel

Project Details


Tutor Perini Civil
Design-Build Contractor
Contract Amount: $1.5 Billion

Fisk Electric Company
Electrical Subcontractor
Contract Amount: $112 Million

Desert Mechanical Inc.
Mechanical Subcontractor
Contract Amount: $77 Million

Frontier-Kemper Constructors, Inc.
TBM Recovery Subcontractor
Contract Amount: $13.6 Million

Becho, Inc.
Drilled-Shaft Subcontractor
Contract Amount: $4.6 Million

Washington State Department of Transportation

Seattle, WA


1.8 Miles


Project Description

The SR 99 Alaskan Way Viaduct is being replaced with an approximately two-mile-long double-deck tunnel underneath downtown Seattle. Replacing the viaduct with a tunnel allows the highway to remain open for much of construction, thus minimizing closures and impacts to traffic. Once the tunnel opens, the viaduct will be taken down to clear the way for new public space along Seattle’s downtown waterfront.

Seattle Tunnel Partners was responsible for designing and building the SR 99 tunnel. In addition to boring the tunnel and building the highway within it, STP is responsible for building highway ramps and other connections at the north and south ends of the tunnel. They are also constructing buildings at each tunnel portal to house lighting, ventilation and other systems needed to operate the tunnel.

“This truly is a remarkable feat of engineering. We've had delays and there’s still work to be done, but the individuals working on this job should be proud of this accomplishment.”
Roger Millar
Washington State Department of Transportation

Photo Credits: WADOT