I-405 is a 30-mile interstate corridor east of Seattle with an average total of approximately 125,000 vehicles using the roadway between SR 527 and I-5 every day. This northern section lacks enough capacity to keep up with those demands. WSDOT needed to respond to public feedback and find solutions to relieve congestion as quickly as possible. Ultimately, the project team developed the innovative dynamic peak-use shoulder lane design, a first in Washington State.
WSDOT developed the design-build contract with the goal of prioritizing early congestion relief and incentivized the design-builder to open the shoulder within 120 days of contract execution. The $11.5 million project was identified and funded in March 2016 and opened to traffic in April 2017, a year ahead of the original schedule identified by the state legislature. Since opening the peak-use shoulder lane, congestion during the northbound afternoon commute from 3 to 7 p.m. has decreased significantly in both the general purpose and express toll lanes, providing benefits for drivers and transit riders alike. Average northbound peak general purpose travel times have decreased by almost half, allowing more vehicles to move through the area.