Interstate 84 or I -84 is an Interstate Highway in the U.S. state of Idaho. The highway runs diagonally through the southwest of the state, calling at the capital Boise. The route is 423 kilometers long. Idaho is a stopover on the long route from Seattle or Portland to Salt Lake City.

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Travel directions

Interstate 84 at Boise.

I-84 through southern Idaho.

Oregon ‘s Interstate 84 crosses the Idaho border at Fruitland. One then enters an irrigated agricultural region, crossing US 95, which runs from southern Oregon to Lewiston. I-84 has 2×2 lanes and passes through one of the more densely populated regions of Idaho. The first larger town is Caldwell, where US 20 and US 26 merge to join I-84, which runs southeast, for a longer distance. Caldwell is followed by the 80,000 inhabitants town of Nampa, more or less a satellite town of Boise. You will then pass through an urban area, including the Meridian suburb of Boise, where the highway has 2×4 lanes. In Boise, Interstate turns 184off, a short link road to downtown Boise. Boise has 212,000 inhabitants and an agglomeration of 635,000 inhabitants.

Immediately after Boise you enter a desert and there are no more exits or suburbs. The next regional town is Mountain Home, where US 20 exits to walk inland to Idaho Falls. One can also follow I-84, I-86 and I-15 to drive to Idaho Falls. After Mountain Home, you pass through remote area again before reaching the valley of the Snake River. One then enters a more densely populated region, that around Twin Falls. At the village of Bliss the US 26 exits and continues inwards to Blackfoot. Following this is a few small towns and you pass Twin Falls, the last larger place before the solitude of southern Idaho.

In Twin Falls one crosses US 93, which runs from Las Vegas to Missoula in Montana. I-84 then temporarily runs due east instead of southeast, parallel to the Snake River. There are also a few places here. At Rupert, I-84 turns southeast, and Interstate 86 continues to Pocatello and Idaho Falls. People come here near mountainous areas. The highway itself runs here at an altitude of 1500 meters. This is another lonely area. At Stone one crosses the Utah border and continues on Interstate 84 in Utah towards Salt Lake City.

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History

I-84’s predecessor is largely US 30. In Burley, US 30 split into US 30N and US 30S, with the later I-84 built parallel to US 30S to the Utah border. Along Twin Falls, I-84 was built closer to State Route 25, as US 30 passed through Twin Falls and I-84 was later built wider north of Twin Falls.

Few exact details of the construction history of I-84 are known. Construction began in the early 1960s and the first routes opened in 1963, from the Oregon state border to near Caldwell, a 30-kilometer stretch northwest of Mountain Home and between Burley and Declo, where I-84 (then I-80N) became I-15W (now I-86). In 1964, extensions opened into Caldwell and the highway between Boise and Mountain Home was open to traffic. This 60-mile stretch was the first long stretch of I-84 to be completed. In the mid-1960s, construction continued on I-84, so by 1967 several routes had been put into use, such as between Caldwell and Meridian, and a longer stretch between Jerome and Burley, which still had a short missing link west of Burley. By 1969, I-84 between Meridian and Boise had been opened, leaving only the Boise bypass missing. Also, the little missing link opened west of Burley. At the end of 1969 the southernmost part of the highway between Declo and the Utah border opened, but this was still a super two for some time.

With this, the longest missing part was between Mountain Home and Jerome. By 1970, the missing bypass of the capital Boise opened, allowing I-84 to pass through for 150 miles between the Oregon border and Mountain Home, and for 100 miles between Jerome and the Utah border. By 1972, the Jerome Bypass opened a short stretch west of Bliss and an extension from Jerome to Wendell. The missing sections are believed to have opened in 1973-1974, as the Interstate Highways network in Idaho was considered complete in 1974.

The highway was originally numbered I-80N, which was changed to I-84 in 1980.

Widenings

Interstate 84 runs through the booming region around Boise. Ada County doubled from 200,000 to 400,000 residents between 1990 and 2010, and Canyon County also more than doubled from 90,000 in 1990 to 190,000 in 2010.

Until the early 1990s, I-84 still had 2×2 lanes. In the mid-1990s, the first section was widened to 2×3 lanes between SR-55 and I-184 west of Boise. By 2003, this section was widened further west to SR-69 in Meridian to 2×3 lanes. At the same time, the section between SR-55 and I-184 was further widened to 2×4 lanes in 2003. In 2009-2010, two further sections of I-84 were widened, e.g., the section from Meridian to Nampa was widened to 2×4 lanes, and widened the portion along the south side of Boise, between I-184 and US 26, to 2×4 lanes. In 2014-2015, I-84 was widened through to 2×4 lanes at SR-69 in Meridian. This project was completed on November 24, 2015. With this, I-84 from Nampa to the south side of Boise has through 2×4 lanes.

Traffic intensities

In 2013, 16,500 vehicles crossed the Oregon border daily, increasing to 116,500 for Boise, as this is an urbanized corridor. After Boise, the intensities quickly drop to about 15,000 to 20,000 vehicles per day. After the I-86 branch, this decreases further to barely 7,000 vehicles per day.