Tacoma Narrows Bridge—Pierce County, WA
Client
- Washington State Department of Transportation
Project Value 
$786,000,000 (Total Constructed Value)
Market
Bridge, Transportation
Services
Engineering
The Tacoma Narrows Bridge design-build project included the new Tacoma Narrows Parallel Bridge, a 5,400 ft. long, three-span suspension bridge constructed within 200 ft. of the existing historic suspension bridge in Tacoma, Washington. The bridge work included the new caissons, towers, anchorages, suspension system, stiffening truss, and deck. The approach roadway work for State Route 16 included 2.5 miles of highway realignment and widening from four to six lanes, a new interchange bridge and ramps, signing, striping, a pump station, drainage, retaining walls, lighting and toll facilities. Upgrades to the existing suspension bridge were included in order to modify the deck/barrier system and provide seismic improvements.
An Engineering Marvel: The New Tacoma Narrows Bridge
The new 854 meter main span suspension bridge opened to traffic on July 16, 2007. It carries four eastbound traffic lanes of State Route -16 between Gig Harbor and Tacoma.
The new Tacoma Narrows bridge is the first major suspension bridge in the world to be constructed under a design-build contracting arrangement, with a fixed price and firm delivery date.
The Bridge’s two 155 meter tall reinforced concrete towers are founded on massive reinforced concrete gravity caissons of open-dredge construction. Gravity anchorages on the hillsides of the Narrows serve to secure the suspension cables. The suspended superstructure consists of 7.2 meters deep and 1,646 meters long continuous welded steel trusses with integral orthotropic steel deck. Allowances have been made in design to accommodate a future lower roadway or light rail transit (LRT) system.
Wind And Seismic Considerations
The Tacoma Narrows Bridge project addressed two major design challenges: wind performance and seismic safety.
Navigating Wind Issues
Because the bridges stand only 55 meters apart, unprecedented wind tunnel testing with side-by-side aeroelastic models was conducted at the National Research Council of Canada, ensuring aerodynamic stability and eliminating interference risks.
Ensuring Seismic Safety
A performance-based seismic design approach was adopted, accounting for earthquakes with return periods of 100 and 2,500 years. Extensive soil-structure interaction modeling verified tower and caisson behavior under seismic loading.
Together, these efforts demonstrated that rigorous wind and seismic design criteria can achieve safe, economical, and resilient long-span suspension bridge performance.
Value Added
The congestion that resulted after 57 years of service from the 1950 bridge has been completely eliminated by the opening of the new bridge, coupled with an efficient toll collection using electronic toll tags.
The public has been enthusiastic about the resulting time savings on daily commutes. WSDOT considers the project successful in every regard, noting the budget performance by the contractor, close adherence to schedule and achieving high quality construction standards. Adopting the design-build delivery method for this large-scale project, coupled with international procurement, fabrication and delivery methods, was paramount to the project’s success.
