Tetra Tech INCA was a significant contributor as a designer of the Puget Sound’s premier transportation program of the 1980s, the improvements to the I-90 corridor across Mercer Island. This $23,000,000 construction effort was a major undertaking of WSDOT, resulting in several new approaches for integrating of landscape, transit, and community access. INCA provided preliminary design of the eight-lane depressed freeway, including landscaped cut and cover overpasses, aerial ramps, and transit access. INCA provided value engineering services and final design for numerous retaining walls with several construction techniques.