State Route 21 and 22 in Idaho

State Route 21 in Idaho

Get started Boise
End Stanley
Length 131 mi
Length 211 km
BoiseIdaho City



State Route 21 or SH-21 is a state route in the U.S. state of Idaho. The road forms a north-south route through the wilderness of Central Idaho, from the capital city of Boise to Stanley. The road is 211 kilometers long. The road also forms the Ponderosa Pine Scenic Byway tourist route.

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Travel directions

State Route 21 begins southeast of the state capital Boise at its junction with Interstate 84. The road here leads through the edge of town at 950 meters and crosses the Boise River, after which there is a short section of 2×2 lanes to the Lucky Peak Dam. Then the State Route 21 leads through the Boise National Forest, this is a quiet, later even lonely route through remote wilderness. Closer to Boise there are still some houses along the road, after Idaho City the area gets very lonely. There are virtually no intersecting roads on this route.

The road here ascends to the first mountain pass, the 1,865-foot Mores Creek Summit. The mountains in the area are up to approximately 2,400 meters high. The road then descends to approximately 1,600 meters, followed by a second mountain pass of approximately 1,850 meters. Then follows a steep descent to the canyon of the Payette River at 1,160 meters. This is where the hamlet of Lowman is located. State Route 21 then follows the Payette River eastward. This route enters the Sawtooth Range, a high mountain range with peaks up to approximately 3,200 meters. The road rises here to the 2,145 meter high Banner Summit. The road then descends to Stanley, a hamlet at 1,900 feet where the road ends at State Route 75.

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State Route 21 along the Boise River at Lucky Peak Dam.

Idaho City has its origins as a mining town. In the 1860s, a turnpike was constructed between Boise and Idaho City. The other parts of the road lead through remote wilderness and were built much later. The higher mountain passes are sometimes closed in winter.

Ponderosa Pine Scenic Byway

The entire route coincides with the Ponderosa Pine Scenic Byway, a scenic byway with the theme of Pinus ponderosa, a type of pine tree that can reach a height of 70 meters. The scenic byway is listed as one of the most remote in the United States, with more acres of roadless wilderness than anywhere else in the 48 contiguous states. On the entire 211 kilometer route there is only one other intersecting road, a forest service road to Garden Valley.

Traffic intensities

7,000 vehicles drive daily at Boise, dropping to 2,000 vehicles as far as Idaho City and 400 vehicles after Idaho City. The long route from Idaho City to Stanley has only 200 to 600 vehicles per day.

State Route 22 in Idaho

Begin Howe
End Dubois
Length 44 mi
Length 71 km

State Route 22 or SH-22 is a state route in the U.S. state of Idaho. The road forms an east-west link in the east of the state, from near Howe to Dubois. The road is 71 kilometers long.

Travel directions

State Route 22 runs from State Route 33 east of Howe to Interstate 15 at Dubois. There is no place directly on the route. The road is single-lane and leads through flat terrain, but close to the mountains of Central Idaho. The main intersection on the route is with State Route 28.


The original State Route 22 ran from Mountain Home to Trude, a much longer east-west route that ran partly in the same area as today’s State Route 22. This later largely became US 20. The current route was originally State Route 29.

State Route 22 is today the fastest and shortest route between western Idaho and I-15 toward Montana. The highway route via I-84, I-86 and I-15 goes further south and further north there are no good east-west routes because of the mountains.

Traffic intensities

State Route 22 is very light with only 250 to 500 vehicles per day.

State Route 22 in Idaho