Interstate 405 Widening Project

The new widened Interstate 405 will add greater capacity through two new southbound auxiliary lanes. Credit: Flatiron Construction Corporation.

Dual express toll lane system will be installed between SR167 in Renton and NE 6th Street in Bellevue. Credit: Flatiron Construction Corporation.

Washington State Department of Transportation (WSDOT) is undertaking the project with an investment of $705m. Credit: Flatiron Construction Corporation.

The Washington State Department of Transportation (WSDOT) is undertaking the Interstate 405 widening project to ease traffic congestion between Renton and Bellevue in Washington, US.

The $750m project will involve the development of a multi-modal transport system, ensuring the rapid and reliable movement of riders and freight. The project will also install a dual express toll system between Northeast 6th Street in Bellevue and State Route 167 in Renton, Washington.

WSDOT issued a notice to proceed with the I-405 widening works in October 2019. Construction of the widening and dual expressway is expected to begin in 2020 and be completed in 2024.

Interstate 405 widening project details

The Interstate 405 widening project will add a toll lane in both directions of the highway. The existing high-occupancy vehicle (HOV) lane will be merged with the new lane to create a dual express toll lane system.

New toll lanes will intersect with the existing toll lane system between Lynnwood and Bellevue. In addition, the lanes will be connected to the SR 167 HOT lanes through the I-405/SR 167 Interchange Direct Connector, creating 64km of express toll lanes.

A portion of the 67.6km-long Eastside Rail Corridor Trail will also be developed as part of the project, including a 4km-long paved section and a new crossing for the I-405 in downtown Bellevue at the Wilburton rail bridge.

A direct access ramp and inline transit station will be built at NE 44th Street in Renton, which is expected to support bus rapid transit operations.

The number of lanes on the southbound I-405 to eastbound I-90 ramp will be increased from one to two as part of the ramp configurations. The two-lane northbound I-405 to SR 520 ramp will be expanded with a third lane.

The project will include the construction of an overpass and bridge improvements at SE 8th Street and Main Street.

Construction of Interstate 405

A braided ramp bridge will be constructed to separate vehicles entering and exiting I-405 at the interchange with state route 522. This is aimed to ease congestion and increase safety. Other works include the installation of a new intelligent transportation system network, widening and retrofitting an existing bridge, installation of noise walls, and resurfacing a portion of the existing freeway.

Major interchange works of the project include the replacement of the 112^th Avenue SE interchange bridge structure over I-405, as well as replacement of northbound and southbound I-405 bridge structures over May Creek.

Approximately 15,000 linear feet of new media filter drains and 10,000 linear feet of compost-amended biofiltration swale will also be installed. Two fish passage crossings under NE 44^th Street and I-405 will be created and new noise walls constructed, while the existing noise walls will be relocated.

The project also covers the construction of stormwater management and water quality facilities, permanent signage, pavement markings, illumination, tolling gantries, and barriers.

Contractors involved in Interstate 405 widening project

The joint venture (JV) between Flatiron West and Lane was awarded the design-build contract for the project, in October 2019.

Flatiron Construction subsidiary Flatiron West will be responsible for providing construction and engineering services for the I-405 project. Salini Impregilo subsidiary Lane Construction is responsible for providing solutions for sustainable mobility and minimising traffic congestion on I-405.

Hart Crowser was awarded the contract to provide geotechnical engineering services for the I-405 widening project.