New Frontiers in the Northwest: I-405 Project Underway

Crews work on an operation to widen and retrofit an existing bridge as part of the I-405 project near Seattle, Washington.

Work is well underway on Flatiron Construction’s first project in the Northwest – the Interstate 405 project in Washington. Flatiron is widening and installing express toll lanes from Bellevue to Lynnwood, Washington, a major artery running along the east side of Lake Washington near Seattle. The $155.5 million design-build project will relieve congestion along 17 miles of the interstate by adding tolling infrastructure and an additional lane in each direction. Crews are also constructing a braided ramp bridge to separate vehicles entering and exiting I-405 at the interchange with state route 522, further easing congestion and increasing safety. Other work includes a new Intelligent Transportation System network, widening and retrofitting an existing bridge, adding noise walls, upgrading barriers and resurfacing much of the existing freeway.

The project is intersected by State Route 522, which cuts it in half.

“North of 522, we’re installing tolling infrastructure and doing some repaving,” explained deputy project manager Shawn Marvin. “South of 522 we’re also widening the roadway by adding a lane in each direction, and repaving the entire roadway.”

Crews are building ductbank, foundations, overhead structures and signage in preparation for tolling equipment which will be installed under a separate contract. The system will use dynamic tolling, charging drives based on traffic volume—more during rush hour, and less in off-peak times.

Along the entire corridor, crews are also retrofitting the roadway with advanced storm water treatment systems – essentially new ditches that include filtration media to capture pollution in runoff. Crews will install 15,000 linear feet of new media filter drains, and, for the first time on a WSDOT project, 10,000 linear feet of a more advanced version called a compost-amended biofiltration swale. Flatiron is also performing extensive wetland and stream mitigation work, part of an effort by owner Washington State Department of Transportation to improve water quality and restore salmon habitat throughout the state. As part of this effort Flatiron recently rehabilitated a portion of Yarrow Creek adjacent to the project.

“WSDOT’s upped the ante on what they do environmentally. All of our design had to meet their new criteria, and if we found existing deficient systems, we had to update or retrofit them,” said Shawn.

Flatiron’s offices are co-located with the team from WSDOT and designer URS.  The design phase of the project is now about 95 percent complete. Flatiron is partnering closely with WSDOT, which Shawn credits with helping to overcoming some unforeseen design challenges.

“As far as the collaboration process and getting things done, it’s much more efficient. We do a lot of over the shoulder design and are able to schedule impromptu meetings when needed. We were able to resolve many design issues early in the process—it went a lot smoother than most people anticipated. We all worked together to make this thing successful,” said Shawn.

Flatiron and designer URS incorporated some innovations into their design that were critical to winning the project. For example, the WSDOT plan allowed for one full closure, while Flatiron proposed completing the project without any full closures.  The team was also able to propose slightly shifting toll zones in either direction so dual toll structures could be installed, further driving down construction costs.

“One innovation was that the original design had a giant cut wall in an area with an historic slide,” said Shawn. “We changed both the alignment of WSDOT’s project design and the future Master Plan design to eliminate the need to build a wall and excavate 200,000 cubic yards of material.  We were the only bidder to eliminate the wall and we think it was one of the biggest changes we made at bid time to lower our price and get the job.”

Flatiron has about 40 employees on the job, the company’s first in the state. Shawn sees a lot of potential for growth for Flatiron in the area, both in traditional bid-build work and on design-build projects. “We’re looking at a few other transportation infrastructure projects coming out in the area in the next year,” said Shawn. “WSDOT is very sophisticated in the use of design-build. They’ve been using it for the past 10 years or more. They were one of the first public owners in Washington to adopt it, and other transportation owners look to WSDOT’s program as a model.”

In addition, Washington’s highway tolling system is in its infancy and WSDOT plans an additional 25 miles of tolling facilities under Design-Build procurements in the near future.  Flatiron’s experience on this project makes us uniquely positioned amongst other contractors in pursuit of this work.

The I-405 project officially started in February 2012, and construction began the following July. The new toll lanes are slated to open at the end of September 2015, but the majority of Flatiron’s work will be complete in late 2014. A smaller crew will then provide support to the toll equipment contractor through the installation and testing phases and then restripe for the toll lanes, open the braided ramp and complete other finishing touches on the job.