U.S. Route 26 in Idaho

After crossing the Snake River at the Oregon state line, US 26 and US 20 make a curve towards 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 BL 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: SH-16, SH-55 in Eagle–Boise 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 3⁄4 mile (1.2 km). 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 (72 km/h) curve and then becomes an at-grade one-way pair.[3]

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 the 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 miles (140 km). 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 BL, 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 towards 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 BL.[3]

At this point, US 26 begins to run concurrently with I-15 for the next 23 miles (37 km). All of 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 BL. Both routes then cross the Snake River (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 BL branches westward towards 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.[3]