Wikipedia

U.S. Route 20 in Idaho

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

U.S. Highway 20(US 20) is the portion of an east–westUnited States Numbered Highwayin the state ofIdaho.It begins northwest ofParmaat the Oregon state line and enters Montana 9.6 miles (15.4 km) away from theYellowstone National Parkwest entrance.

U.S. Highway 20 marker
U.S. Highway 20
Idaho Medal of Honor Highway
Map
US 20 highlighted in red
Route information
Maintained byITD
Length406.30 mi[1](653.88 km)
Existed1940[2]–present
Major junctions
West endUS 20/US 26at theOregonstate line
Major intersections
East endUS 20at theMontanastate 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

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

Route description

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I-15/US 20 junction in Idaho Falls

At the western border, adjacent toNyssa, Oregon,US 20 (running concurrentlywithUS 26) crosses theSnake Riverinto Idaho at an approximateelevationof 2,200 feet (670 m) abovesea level.It joinsUS 95and runs southbound toParma.US 20/US 26 leaves US 95 southeast of Parma and runs toCaldwell,where it briefly joinsInterstate 84(I-84; andUS 30) from exit 26 until exit 29.

These four highways parallel each other east (on two roadways) toBoisewhere 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 toMountain Home,where US 20 departs at exit 95 to head east, pastRattlesnake Station,Anderson Ranch Damroad, and crests at Cat Creek summit at 5,527 feet (1,685 m). This portion of the route is nearGoodale's Cutoffof theOregon Trail.

US 20 continues east, into, and acrossCamas CountythroughFairfieldto Timmerman Junction, the intersection inBlaine CountywithState Highway 75(SH-75), the northbound route toSun Valley,Galena Summit,andStanley.US 20/US 26 goes throughPicaboandCarey,joins withUS 93,and on toCraters of the Moon National Monument and PreserveandArco,where US 93 splits off and turns north-northwest to climb theBig Lost Rivervalley.

US 20/US 26 continues on throughIdaho National Laboratory,where the highways split just west ofAtomic City;US 26 heads southeast toBlackfootand US 20 toIdaho Falls,where it turns north-northeast to pass nearRexburgas a freeway. US 20 then climbs through the communities ofSt. Anthony,Ashton,andIsland Park,and crosses theContinental DivideatTarghee Passat 7,072 feet (2,156 m), enteringMontanawest ofWest Yellowstone.

History

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US 20 was expanded past Yellowstone National Park in 1940, replacing the originalUS 191and 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

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CountyLocationmi[1]kmExitDestinationsNotes
Snake River0.0000.000

US 20west /US 26west –Nyssa		Continuation into Oregon
Snake River Bridge; Oregon–Idaho state line
Payette–Canyon
county line		​1.5782.540
US 95north –Fruitland,Payette		Western end of US 95 concurrency
Canyon​9.64715.525
US 95south –Jordan Valley		Eastern end of US 95 concurrency
Caldwell21.995–
22.129		35.398–
35.613
I-84/US 30west –Ontario		Western end of I-84/US 30 concurrency; I-84 exit 26
22.6–
23.1		36.4–
37.2		27

I-84 BLeast toSH-19–Caldwell,Wilder,Homedale		Exit numbers follow I-84
23.5–
24.1		37.8–
38.8		2810th Avenue –City Center
24.840–
24.994		39.976–
40.224
I-84/US 30east –Nampa,Boise		Eastern end of I-84/US 30 concurrency; I-84 exit 29
Ada​34.26755.147SH-16–Emmett
Boise–Eagleline40.22964.742SH-55–Caldwell,Eagle
Garden City44.16671.078SH-44–Eagle
Boise47.20575.969—Main StreetWestern end of freeway; westbound entrance only
47.30076.122—

I-184west toI-84		Eastern terminus of I-184; westbound left exit and eastbound left entrance
48.05077.329—River StreetEastbound exit only
48.51278.072—Front Street westEastern end of freeway; westbound exit only
51.96083.622Federal WayInterchange
52.681–
52.824		84.782–
85.012
I-84/US 30west / Commerce Avenue –Nampa		Western end of I-84/US 30 concurrency; I-84 exit 54
55.389.057SH-21(Gowen Road) –Idaho CityExit numbers follow I-84
​57.993.259S. Eisenman Road, Memory RoadSigned as exits 59A (S. Eisenman Road) and 59B (Memory Road) eastbound
​61.999.664Blacks Creek Road –Kuna
Regina69.2111.471Mayfield,Orchard
Elmore​72.8117.274Simco Road
​88.7142.790


I-84 BLeast toSH-51/SH-67–Mountain Home,Bruneau		Eastbound signage
West Mountain HomeWestbound signage
Mountain Home95.308–
95.467		153.383–
153.639

I-84/US 26/US 30east /I-84 BLwest (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
CamasFairfield156.157251.310SH-46–Gooding,Wendell
Blaine​178.095286.616SH-75–Shoshone,Challis
Carey196.039315.494US 26/US 93–Bliss,Twin FallsWestern end of US 26/US 93 concurrency
ButteArco248.555400.010US 93–ChallisEastern end of US 93 concurrency
Butte City256.073412.110SH-33–Howe
Atomic City263.77424.50US 26–Idaho FallsEastern end of US 26 concurrency
Bingham
 No major junctions
BonnevilleIdaho Falls306.9493.9


I-15south /I-15 BL/US 20 Bus.(Broadway Street east) toUS 26–Blackfoot,Pocatello,Jackson,Idaho Falls		Western end of I-15 concurrency; I-15 exit 118
307.617495.062
I-15north –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
307.72–
307.87		495.23–
495.47		307Lindsay Boulevard
307.967–
308.318		495.625–
496.190		308ARiverside Drive – City CenterSigned as Exit 308 eastbound
308.504496.489308BScience Center DriveEastbound exit and westbound entrance
​309.585–
310.125		498.229–
499.098		310
US 20 Bus.–Lewisville
Orvin310.99–
311.739		500.49–
501.695		311Saint Leon Road, 15th East
​313.063–
313.887		503.826–
505.152		313Hitt Road, 25th East
Ucon314.92–
315.57		506.81–
507.86		315SH-43–Ucon
Bonneville–Jefferson
county line		​317.559–
318.367		511.062–
512.362		318County Line Road
JeffersonRigby320.375515.594320

US 20 Bus.toSH-48–Rigby		Eastbound exit and westbound entrance
322.083–
322.586		518.342–
519.152		322
US 20 Bus.– North Rigby		Eastbound signage


US 20 Bus.toSH-48–Rigby		Westbound signage
Lorenzo325.202–
325.898		523.362–
524.482		325Menan,Roberts
Snake River326.2525.0Bridge
Madison​328.232528.238328Thornton
Rexburg331.63–
332.27		533.71–
534.74		332BYU-Idaho,South Rexburg
333.198–
333.77		536.230–
537.15		333SH-33–Salmon,Rexburg
336.53–
337.098		541.59–
542.507		337North Rexburg
Sugar City338.018543.987338Sugar City,SalemEastbound exit and westbound entrance
338.522–
339.295		544.798–
546.042		339

ToSH-33east –Driggs,Jackson,Sugar City		Eastern end of Rigby Freeway
Fremont​343.64553.03344South St. AnthonyNew interchange under construction
St. Anthony345.2–
345.91		555.5–
556.69		346

US 20 Bus.east –St. Anthony		Interchange
​347.851559.812

US 20 Bus.west –St. Anthony
Ashton360.572580.284
SH-47toSH-32–Driggs
Island Park402.27647.39SH-87–Ennis
Continental Divide406.3653.9Targhee Pass;Idaho–Montana state line

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

References

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  1. ^ab"Milepoint Log — State Highway System: US 20"(PDF).Idaho Transportation Department.January 25, 2016.RetrievedFebruary 10,2023.
  2. ^abWeingroff, Richard (October 17, 2013)."Ask the Rambler: What Is the Longest Road in the United States?".Federal Highway Administration.RetrievedDecember 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.RetrievedAugust 27,2021.
  4. ^"Drivers ease on down Boise's new roadway".The Idaho Statesman.August 8, 1992. p. 1A.RetrievedFebruary 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.RetrievedFebruary 10,2023.
  6. ^"Thornton Interchange opens, U.S. 20 improvements now complete".East Idaho News. November 18, 2016.RetrievedJuly 16,2018.
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KML file(edit•help)
Template:Attached KML/U.S. Route 20 in Idaho
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U.S. Route 20
Previous state:
Oregon 		Idaho Next state:
Montana
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