The Everett-Seattle-Tacoma Superhighway was planned in 1951, and the legislature approved it in 1953. The Federal Defense Highway Act of 1956 made the project possible. One of the first voices to rise against the route was former Seattle Mayor George Cotterill (1865-1958), who was concerned about the effects of building the route through a slide-prone area. Residents of First Hill were concerned about the separation of their neighborhood from the rest of the city and about pollution and noise. Architect Paul Thiry (1904-1993) supported a lid over the freeway where businesses and apartments could be built. Downtown interests were concerned about the loss of parking spaces and the increase in traffic.
The federal government would not pay for these enhancements and state officials, including Governor Albert Rosellini (1910-2011), were unwilling to delay the project. The freeway opened in 1967.