The Ellensburg-Pendleton corridor was authorized in 1956 but was not formally added to the Interstate system until October 17, 1957. The corridor was proposed by the Department of Defense and Washington senator Warren Magnuson in part to connect military facilities in the Puget Sound region to the Hanford Site and the Umatilla Chemical Depot but its inclusion was initially opposed by Oregon and Washington. Under the initial plan approved by the Washington state government in January 1958, the highway would travel through the Yakima Valley and cross the Columbia River at Boardman, Oregon, bypassing the Tri-Cities region entirely. It was numbered Interstate 82 in 1958, re-using an older designation for what would become Interstate 80N (now I-84). In 1959, the Washington State Highway Commission requested that the interstate would follow US 410 across Naches Pass to Tacoma and Aberdeen, but the proposal was quietly abandoned.