U.S. Route 26 in Idaho

U.S. Highway 26 (US-26) runs east–west across south central Idaho for 402.5 mi. US-26 enters the state from Oregon across the Snake River east of Nyssa, Oregon, concurrent with US-20 and exits into Wyoming northwest of Alpine. US-26 runs through the large population centers of Boise and Idaho Falls, as well as the smaller communities of Parma, Notus, Garden City, Shoshone, Richfield, Carey, Arco, Blackfoot, Swan Valley, and Irwin.

For a vast majority of its route, US-26 is two lanes and rural, with the exception of portions in and around major towns and cities. It does have significant four-lane segments within the Boise metropolitan area and east of Idaho Falls. Despite its extensive length, US-26 has many hundreds of miles that run concurrently with other highways. In fact, its first 138.97 mi in the state consists of concurrencies with any one of five different highways, principally US-20 and Interstate 84 (I-84). It has additional lengthy concurrencies with US-93, US-20 again, and I-15.

US-26 does have one business route in the state of Idaho, which runs through the small community of Ririe northeast of Idaho Falls.

Oregon state line to Downtown Boise
After crossing the Snake River at the Oregon state line, US-26 and US-20 make a curve toward US-95. At that point, both routes travel south along US-95. The three routes then travel south and then curves southeast in Parma. Then, US-95 branches southward while the rest continues southeast. Both US-26 and US-20 pass through Notus before meeting I-84/US-30. At this point, the four routes meet I-84 Business (I-84 Bus.) and then 10th Avenue before US-20 and US-26 travel east on Franklin Road; all of the exits are in Caldwell.

As the two routes approach Boise, they intersect three state highways: State Highway 16 (SH-16), SH-55 on the Eagle–Boise city line, and SH-44 in Garden City. In Boise, as US-26 and US-20 merge eastward onto I-184, the Interstate designation ends there but the freeway ends in about 0.75 mi. Just after the freeway crosses the Boise River, both routes traveling eastbound serve River Street and Bogus Basin. After this, the freeway approaches a 45 mph curve and then becomes an at-grade one-way pair.

Downtown Boise to Blackfoot
As both routes exit downtown, they turn south and become a two-way street. Also, the two routes cross the Boise River for the second time. After that, they run along the eastern edge of Boise State University. As they approach Boise Airport, they then turn east onto I-84/US-30 again. This time, US-26 runs concurrently with I-84 for about 87 mi. Along the way, the freeway serves several state highways, I-84 business loops, and local roads in different locations. At one point east of Mountain Home, US-20 leaves the freeway and travels northeastward. As the freeway reaches Bliss, US-30, along with I-84 Bus., leaves the freeway as Thousand Springs Scenic Byway. At the next exit, US-26 leaves the freeway.

US-26 went on to serve a handful of state highways in Gooding and Shoshone. Also in Shoshone, the route begins to run concurrently with US-93. Both routes then serve Richfield. In Carey, they begin to run concurrently with US-20. For US-26, this is the second time in Idaho. The three routes serve Craters of the Moon National Monument and Preserve and Blizzard Mountain Ski Area. In Arco, US-93 branches northwestward. The rest continues eastward through Butte City and serving SH-33. Just southeast of the base of Idaho National Laboratory, US-26 branches southeast toward Blackfoot while US-20 continues east. As US-26 approaches Blackfoot, the route intersects SH-39 and then crosses over the same Snake River. Shortly after that, it turns northeast onto I-15 while the road continues as I-15 Bus.

Blackfoot to Wyoming state line
At this point, US-26 begins to run concurrently with I-15 for the next 23 mi. All the interchanges within this concurrency lead to local roads. As the freeway enters Idaho Falls, US-26 leaves the freeway and turns east along I-15 Bus. Both routes then cross the Snake River (the third time for US-26) and then intersect the northern terminus of US-91. At this point, both travel north toward downtown Idaho Falls. In downtown, I-15 Bus. branches westward toward I-15/US-20. Continuing northeast, US-26 intersects several more routes: SH-43 in Beachs Corner, US-26 Bus. (twice) near Ririe, and SH-31 in Swan Valley. Continuing eastward, US-26 travels along the bank of Snake River and then enters Wyoming.

History
When US-26 was initially designated in the state in 1951, it ran only as far west as Idaho Falls. The next year, it was extended into Oregon.

In the Idaho Falls area, US-26 runs along local streets and county roads. In 2022, the Idaho Transportation Board approved a study into relocating parts of the highway onto US-20 following the reconstruction of the I-15/US-20 interchange at the west end of the Rigby Freeway.

Ririe business route
U.S. Highway 26 Business (US-26 Bus.) is a 2.981 mi business route in and around the small town of Ririe northeast of Idaho Falls. It connects US-26 to the community as well as SH-48.

Major intersections