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U.S. Route 20 in Idaho

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This article is about the section of U.S. Route 20 in Idaho. For the entire route, see U.S. Route 20.

U.S. Highway 20 marker
U.S. Highway 20
Idaho Medal of Honor Highway
Map
US 20 highlighted in red
Route information
Maintained by ITD
Length406.30 mi[1] (653.88 km)
Existed1940[2]–present
Major junctions
West end US 20 / US 26 at the Oregon state line
Major intersections
East end US 20 at the Montana state line
Location
CountryUnited States
StateIdaho
CountiesPayette, Canyon, Ada, Elmore, Camas, Blaine, Butte, Bingham, Bonneville, Jefferson, Madison, Fremont
Highway system
  • Idaho State Highway System
← SH-19→ SH-21

U.S. Highway 20 (US 20) is the portion of an east–west United States Numbered Highway in the state of Idaho. It begins northwest of Parma at the Oregon state line and enters Montana 9.6 miles (15.4 km) away from the Yellowstone National Park west entrance.

Since 2019, US 20 has been designated as the Idaho Medal of Honor Highway.[3]

Route description

[edit]
I-15/US 20 junction in Idaho Falls

At the western border, adjacent to Nyssa, Oregon, US 20 (running concurrently with US 26) crosses the Snake River into Idaho at an approximate elevation of 2,200 feet (670 m) above sea level. It joins US 95 and runs southbound to Parma. US 20/US 26 leaves US 95 southeast of Parma and runs to Caldwell, where it briefly joins Interstate 84 (I-84; and US 30) from exit 26 until exit 29.

These four highways parallel each other east (on two roadways) to Boise where US 20/US 26 runs through downtown, then southbound on Broadway Avenue to rejoin with I-84/US 30 at exit 54. The four concurrent routes head southeast to Mountain Home, where US 20 departs at exit 95 to head east, past Rattlesnake Station, Anderson Ranch Dam road, and crests at Cat Creek summit at 5,527 feet (1,685 m). This portion of the route is near Goodale's Cutoff of the Oregon Trail.

US 20 continues east, into, and across Camas County through Fairfield to Timmerman Junction, the intersection in Blaine County with State Highway 75 (SH-75), the northbound route to Sun Valley, Galena Summit, and Stanley. US 20/US 26 goes through Picabo and Carey, joins with US 93, and on to Craters of the Moon National Monument and Preserve and Arco, where US 93 splits off and turns north-northwest to climb the Big Lost River valley.

US 20/US 26 continues on through Idaho National Laboratory, where the highways split just west of Atomic City; US 26 heads southeast to Blackfoot and US 20 to Idaho Falls, where it turns north-northeast to pass near Rexburg as a freeway. US 20 then climbs through the communities of St. Anthony, Ashton, and Island Park, and crosses the Continental Divide at Targhee Pass at 7,072 feet (2,156 m), entering Montana west of West Yellowstone.

History

[edit]

US 20 was expanded past Yellowstone National Park in 1940, replacing the original US 191 and several state highways.[2] Its original alignment through Boise included Main Street and Fairview Avenue for westbound and eastbound traffic, respectively, and Capitol Boulevard. US 20 and US 26 were realigned onto Myrtle and Front streets as well as Broadway following the completion of the Boise Connector extension on August 7, 1992.[4][5]

The Rigby Freeway section of US 20, extending from Idaho Falls to St. Anthony, was constructed in the 1970s. Its northernmost section still featured at-grade intersections until the 2000s, when they were replaced with full interchanges,[6] though a few at grade crossings still exist between Sugar City and St. Anthony as of September 2023.

Major intersections

[edit]
CountyLocationmi[1]kmExitDestinationsNotes
Snake River0.0000.000

 US 20 west / US 26 west – Nyssa		Continuation into Oregon
Snake River Bridge; Oregon–Idaho state line
Payette​1.5782.540
 US 95 north – Fruitland, Payette		Western end of US 95 concurrency
Canyon​9.64715.525
 US 95 south – Jordan Valley		Eastern end of US 95 concurrency
Caldwell21.995–
22.129		35.398–
35.613
 I-84 / US 30 west – Ontario		Western end of I-84/US 30 concurrency; I-84 exit 26
27

 I-84 BL east to SH-19 – Caldwell, Wilder, Homedale		Exit numbers follow I-84
2810th Avenue – City Center
24.840–
24.994		39.976–
40.224
 I-84 / US 30 east – Nampa, Boise		Eastern end of I-84/US 30 concurrency; I-84 exit 29
Ada​34.26755.147 SH-16 – Emmett
Boise–Eagle line40.22964.742 SH-55 – Caldwell, Eagle
Garden City44.16671.078 SH-44 – Eagle
BoiseMain StreetWestern end of freeway; westbound entrance only
47.30076.122—

 I-184 west to I-84		Eastern terminus of I-184; westbound left exit and eastbound left entrance
48.05077.329—River StreetEastbound exit only
—Front Street westEastern end of freeway; westbound exit only
51.97583.646Federal WayInterchange
52.560–
52.664		84.587–
84.754
 I-84 / US 30 west / Commerce Avenue – Nampa		Western end of I-84/US 30 concurrency; I-84 exit 54
57 SH-21 (Gowen Road) – Idaho CityExit numbers follow I-84
​59S. Eisenman Road, Memory RoadSigned as exits 59A (S. Eisenman Road) and 59B (Memory Road) eastbound
​64Blacks Creek Road – Kuna
Regina71Mayfield, Orchard
Elmore​74Simco Road
​90


 I-84 BL east to SH-51 / SH-67 – Mountain Home, Bruneau		Eastbound signage
West Mountain HomeWestbound signage
Mountain Home95.066–
95.307		152.994–
153.382

 I-84 / US 26 / US 30 east / I-84 BL west (SH-51) – Mountain Home, Twin Falls, Air Force Base, Duck Valley		Eastern end of I-84/US 26/US 30 concurrency; I-84 exit 95
CamasFairfield SH-46 – Gooding, Wendell
Blaine​ SH-75 – Shoshone, Challis
Carey US 26 / US 93 – Bliss, Twin FallsWestern end of US 26/US 93 concurrency
ButteArco US 93 – ChallisEastern end of US 93 concurrency
Butte City SH-33 – Howe
Atomic City US 26 – Idaho FallsEastern end of US 26 concurrency
Bingham
 No major junctions
BonnevilleIdaho Falls


 I-15 south / I-15 BL / US 20 Bus. (Broadway Street east) to US 26 – Blackfoot, Pocatello, Jackson, Idaho Falls		Western end of I-15 concurrency; I-15 exit 118

 I-15 north – Roberts, Butte, Airport		Eastern end of I-15 concurrency; I-15 exit 119; access to airport via Grandview Avenue; signalized interchange
Western end of Rigby Freeway
307Lindsay Boulevard
308ARiverside Drive – City CenterSigned as Exit 308 eastbound
308BScience Center DriveEastbound exit and westbound entrance
​310
 US 20 Bus. – Lewisville
Orvin311Saint Leon Road, 15th East
​313Hitt Road, 25th East
Ucon315 SH-43 – Ucon
Bonneville–Jefferson
county line		​318County Line Road
JeffersonRigby320

 US 20 Bus. to SH-48 – Rigby		Eastbound exit and westbound entrance
322
 US 20 Bus. – North Rigby		Eastbound signage


 US 20 Bus. to SH-48 – Rigby		Westbound signage
Lorenzo325Menan, Roberts
Snake RiverBridge
Madison​328Thornton
Rexburg332BYU-Idaho, South Rexburg
333 SH-33 – Salmon, Rexburg
337North Rexburg
Sugar City338Sugar City, SalemEastbound exit and westbound entrance
339

 To SH-33 east – Driggs, Jackson, Sugar City		Eastern end of Rigby Freeway
Fremont​344South St. AnthonyNew interchange under construction
St. Anthony346

 US 20 Bus. east – St. Anthony		Interchange
​

 US 20 Bus. west – St. Anthony
Ashton
 SH-47 to SH-32 – Driggs
Island Park SH-87 – Ennis
Continental DivideTarghee Pass; Idaho–Montana state line

 US 20 east – West Yellowstone, Bozeman		Continuation into Montana
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

References

[edit]
  1. ^ a b "Milepoint Log — State Highway System: US 20" (PDF). Idaho Transportation Department. January 25, 2016. Retrieved February 10, 2023.
  2. ^ a b Weingroff, Richard (October 17, 2013). "Ask the Rambler: What Is the Longest Road in the United States?". Federal Highway Administration. Retrieved December 4, 2014.
  3. ^ Blanchard, Nicole (March 25, 2019). "This Idaho road is now the Medal of Honor Highway. Meet the honorees who crossed its path". Idaho Statesman. Retrieved August 27, 2021.
  4. ^ "Drivers ease on down Boise's new roadway". The Idaho Statesman. August 8, 1992. p. 1A. Retrieved February 10, 2023 – via Newspapers.com.
  5. ^ "Regular Meeting of the Idaho Transportation Board, August 27, 1992" (PDF). Idaho Transportation Department. August 27, 1992. p. 35. Retrieved February 10, 2023.
  6. ^ "Thornton Interchange opens, U.S. 20 improvements now complete". East Idaho News. November 18, 2016. Retrieved July 16, 2018.
[edit]
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U.S. Route 20
Previous state:
Oregon 		Idaho Next state:
Montana
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