Oregon legislators and highway officials remained opposed to a routing that bypassed Umatilla, leading to several attempts at finding a compromise along the Wallula Gap or in other areas southeast of the Tri-Cities.

In 1973, Oregon and Washington adopted a federal compromise to build I-82 through Umatilla and around the outskirts of the Tri-Cities with a spur route (I-182) to serve the area directly.

[2] The four-lane divided highway forms part of the link between Seattle and the inland West, which includes Boise, Idaho and Salt Lake City, Utah.

Here, I-82 also forms the western edge of the Yakima Firing Range, a military training and exercise facility that stretches across the plateau to the Columbia River Gorge.

[24] I-82 and US 395 travel southward and ascend the Horse Heaven Hills to an intersection with SR 397, a highway that provides an alternate truck route for Kennewick and Finley.

Northeast of Plymouth, it intersects the eastern terminus of SR 14, a cross-state highway that follows the Columbia River westward to Vancouver, and crosses the BNSF Fallbridge Subdivision, which carries Amtrak's Empire Builder passenger trains.

[30] The freeway runs along the edge of the Umatilla Chemical Depot and terminates at an interchange with I-84, which is concurrent with US 30, southwest of Hermiston;[15] I-84 and US 30 continue westward along the Columbia River toward Portland and eastward to Pendleton and Boise, Idaho.

[32] In the 1880s, the Northern Pacific Railway constructed a railroad along the Yakima River between Ellensburg and Pasco as part of its transcontinental route to Tacoma via Stampede Pass.

[52] The 132-mile (212 km) 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.

[55] 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.

[57][58] 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.

[59][60] The routing of the freeway's northwestern half was subject to disputes, namely the bypassing of the Yakima River Canyon that was favored by truckers due to its gentler grades.

[53][64][65] I-82's chosen route between Union Gap and Granger would pass through 15 miles (24 km) of the Yakima River's flood plain, attracting criticism from the federal Environmental Protection Agency for its potential effects on the area.

[74][75] The study produced four general corridors, including alternatives that shifted I-82 closer to the Tri-Cities, traversed the area, and continued southeastward along Lake Wallula.

[71][76] The states remained committed to the Umatilla crossing and formally approved the Horse Heaven routing after a two-day public hearing in October 1963.

[73][80] Magnuson later proposed a bill to add 19,000 miles (31,000 km) to the Interstate system, including an allotment for the Tri-Cities,[81] but it failed to advance beyond Congressional committees for several years before quietly excluding I-82.

[89] The Washington State Highway Commission gave preliminary approval to the Wallula route in December 1967, with support from the regional director of the Bureau of Public Roads,[90] but their Oregon counterpart remained opposed.

[91] Oregon governor Tom McCall met with Senator Magnuson to propose a compromise route that would serve the Tri-Cities and the Port of Umatilla, which would later form the basis of a new study begun in mid-1968.

[94] The Washington State Highway Commission approved the compromise in July 1969,[95] but the Oregon delegation expressed its support of the Wallula routing after it was modified to terminate farther west near Stanfield.

[110][111] The 26-mile (42 km) section between Ellensburg and Yakima was funded earlier than scheduled, money being diverted from stalled freeway projects in the Seattle area, and construction began in October 1968.

[114][115] WSDOT contractors built the longest concrete arch spans in North America on the Fred G. Redmon Bridge, which crosses Selah Creek near the city of the same name.

[38][122][123] The freeway's construction created an embankment between the Yakima River and surrounding areas, which helped to worsen major floods; it also required the digging of several gravel pits nearby, which were later converted into seven trout-stocked ponds that feed a local osprey population.

[133][134] The final section of I-82 within Washington state, spanning 17 miles (27 km) from Kiona to an interchange south of Kennewick, was dedicated on February 23, 1986, and opened the following month.

[135][136] During construction of I-82, a pair of fossilized tusks belonging to a mastodon and Columbian mammoth were found by workers near Kiona and Plymouth, respectively, and were excavated by local archaeologists.

[150] I-80N was renumbered to I-84 in 1980 as part of a mandate by American Association of State Highway and Transportation Officials to eliminate suffixed routes and reduce traveler confusion.

[152][153] A 1970s proposal to renumber I-82 to remain in compliance with the numbering scheme was rejected by the Washington State Department of Highways due to the cost of sign replacement and potential for public confusion.

[156] The study found that a new freeway would have little effect on economic growth in eastern Oregon and congestion relief in the Willamette Valley, but would provide a suitable alternative route for long-haul travel.

[159][160] A separate proposal in the early 2010s included a third lane for I-82 in northern Yakima, but it was postponed in favor of the building of a new interchange and east–west road at the Cascade Mill development site.

[161][162] A proposal to add climbing lanes for trucks on the steep grades in the Manastash Ridge between Ellensburg and Yakima was made in the 2000s and remains unfunded as of 2017[update].

[164] Construction of the new interchange, which was intended to divert traffic bound for the winery region and new development near West Richland, was proposed by local politicians in the early 2000s but failed to earn funding from the state.