With a population of 4.1 million, Seattle remains one of the fastest-growing large metropolitan areas in the U.S.
As usual, fast growth means a strained transportation system. In addition, the Seattle metropolitan area is restricted by significant bodies of water like Puget Sound, Lake Washington, Lake Sammamish, Henderson Bay and others.
Together, Interstate 5, Interstate 405, Interstate 90 and State Route 16 handle an immense load of traffic navigating these and other obstacles in the Seattle metro. The Washington State Department of Transportation (WSDOT) has engaged Skanska USA Civil West on a project to ease congestion and eliminate backups.
Skanska is the design-builder in the I-405/Brickyard to SR 527 Improvement Project. This design-build project covers 4.5 mi. through Bothell and Kirkland from just south of the State Route 522 interchange and ending at the State Route 527 interchange.
The complex project will address aging infrastructure and connect communities, freight and regional growth centers throughout this vital corridor.
The project costs $834 million.
Most sections of the project will be in use by the public by the end of 2028.
Pat Prendergast, vice president of operations for Skanska USA Civil West, leads the project.
Prendergast told Construction Equipment Guide that the project is 60 percent complete, with most of the work centered around the I-405/SR 522 interchange.
“We are actively working on the project everywhere at once,” he said. “The new northbound and southbound lanes we are building for the express toll lanes (ETL) will add capacity and should help with congestion.”
Many projects like this would simply add lanes on the outside of the existing road or add lanes in the median between lanes. It is not always possible in this project, as steep dropoffs exist in some areas while bus lanes already fill some medians.
Bridges
In addition to building the new lanes, the Skanska construction team is retrofitting and constructing several bridges.
“Certain components of the project, including some bridges, were built in the 1960s, so bridges had to be upgraded to be able to handle seismic conditions,” Prendergast said. “In many cases, we had to strengthen the pier caps and reinforce the footings.”
The construction team is widening and retrofitting four bridges, building four new pedestrian bridges and constructing four new roadway bridges. Each bridge fulfilled distinct functions within the project.
“One of the bridges will cross over I-405 and carry two lanes of bus traffic,” Prendergast said. “Another was a three-lane ramp bridge which is now complete over the Sammamish River. We are building another bridge in the median to carry four lanes of traffic — two for northbound and two for southbound bus traffic to the interchange for route 522.” The new bridge will conform to seismic guidelines and will eliminate some cloverleafs.
“The Federal Highway guidelines are recommending eliminating cloverleafs where practical. This will be a safer configuration, help with congestion, and provide access for new Bus Rapid Transit Routes and toll entry points.”
A huge piece of the I-405 Brickyard Project entailed constructing a nine-span bridge, with three new general-purpose lanes for the new northbound I-405 over the Sammamish River, Woodinville Drive and SR 522. Ground conditions varied for the bridge.
“In some places, we have to sink the drilled shaft foundations 260 ft., which is extremely deep,” Prendergast said.
Most of the bridge construction will use wide flange concrete girders built by a local supplier. This option was determined to be the most cost-effective and time-efficient.
A project of this size has massive requirements for materials including:
• 150,000 tons of asphalt for the roads;
• 20,000 cu. yds. of concrete;
• 10 million lbs. of reinforcing steel; and
• 30,000 cu. yds. of concrete demolition.
The project team salvaged most of the existing roadway, which was determined before the submittal, so the benefit was seen in the price proposal to WSDOT. The Skanska team determined that the finished road would have adequate depth, including approximately 12-in. thick for the roads and 9-in. thick for the ramps.
The next big feature of the job will be completing the Bus Rapid Transit work for Sound Transit, Seattle's bus and rail system provider, to have full access to the new project area to implement the expansion of their Bus Rapid Transit system on the I-405 and SR 522 corridors.
Fish, Water Issues
While road and bridge work continues, other workers are taking care of special needs for area fish.
“Our team is building six new fish passageways within the project limits,” Prendergast said. “Once constructed and fully permitted, the current culverts that have prevented fish from free access to waterways will no longer be blocked, and fish will be able to navigate these waters unobstructed.”
Other water issues played an important role in the construction.
“Every drop of water that hits the project is collected in an independent water collection system,” he said. “We did erosion and sediment control, so we could efficiently treat the water, then send it to the regular wastewater system.”
Skanska planners are taking some extraordinary steps to protect workers on the project as they build a 280-ft.-long tunnel, 35 ft. under the roadway rather than shifting traffic lanes four or more times on mainline I-405 and constructing bridges at each step.
“We decided to use ground-freezing technology to advance the tunnel using a Sequential Excavation Method Tunnel,” Prendergast said. “Our team will introduce a brine into the soil, freeze the ground and create a shotcrete-reinforced arch.” The arch will serve as the final structural element upon the tunnel's completion.
This additional work also added a much safer avenue for workers to get to their jobs, especially during night-paving operations, which are the most accident-prone.
“This effort allowed our people to do their jobs away from traffic,” Prendergast said. “At the same time, it cut some 50,000 worker-hours that would have directly interfaced with the traveling public and no longer has to.”
Safety officers for the project also provided abundant notifications to drivers, outfitted trucks with vibrant lighting and refitted trucks to enable workers to pick up traffic cones from the side of the truck away from vehicle travel, further shielding workers from inattentive or compromised drivers.
As sections of the I-405 Brickyard Improvement Project come online, motorists will notice a difference. They will also have additional travel options. As time passes, WSDOT envisions a full reconstruction of the I-405/SR 167 corridor, a goal that will encompass approximately 50 miles in all.
“Our project will make it easier for people to ride buses, use toll lanes and reduce the number of cars overall,” Prendergast said. “That means fewer cars, fewer emissions and more capacity for travelers.”
