U.S. Route 20 in Idaho
U.S. Highway 20 | ||||
|---|---|---|---|---|
| Idaho Medal of Honor Highway | ||||
US 20 highlighted in red | ||||
| Route information | ||||
| Maintained by ITD | ||||
| Length | 406.30 mi[1] (653.88 km) | |||
| Existed | 1940[2]–present | |||
| Major junctions | ||||
| West end |   US 20 / US 26 at the Oregon state line | |||
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| East end | US 20 at the Montana state line | |||
| Location | ||||
| Country | United States | |||
| State | Idaho | |||
| Counties | Payette, Canyon, Ada, Elmore, Camas, Blaine, Butte, Bingham, Bonneville, Jefferson, Madison, Fremont | |||
| Highway system | ||||
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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
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
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]
Junction list
 | This section contains a table that is missing mileposts for one or more junctions. |
| County | Location | mi[1] | km | Exit | Destinations | Notes |
|---|---|---|---|---|---|---|
| Snake River | 0.000 | 0.000 |  US 20 west / US 26 west – Nyssa | Continuation into Oregon | ||
| Snake River Bridge; Oregon–Idaho state line | ||||||
| Payette | | 1.578 | 2.540 |   US 95 north – Fruitland, Payette | Western end of US 95 concurrency | |
| Canyon | | 9.647 | 15.525 |  US 95 south – Jordan Valley | Eastern end of US 95 concurrency | |
| Caldwell | 21.995– 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 | ||||
| 28 | 10th 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 | | 34.267 | 55.147 |  SH-16 – Emmett | ||
| Boise–Eagle line | 40.229 | 64.742 |  SH-55 – Caldwell, Eagle | |||
| Garden City | 44.166 | 71.078 |  SH-44 – Eagle | |||
| Boise | Main Street | Western end of freeway; westbound entrance only | ||||
| 47.300 | 76.122 | — |    I-184 west to I-84 | Eastern terminus of I-184; westbound left exit and eastbound left entrance | ||
| 48.050 | 77.329 | — | River Street | Eastbound exit only | ||
| — | Front Street west | Eastern end of freeway; westbound exit only | ||||
| 51.975 | 83.646 | Federal Way | Interchange | |||
| 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 City | Exit numbers follow I-84 | ||||
| | 59 | S. Eisenman Road, Memory Road | Signed as exits 59A (S. Eisenman Road) and 59B (Memory Road) eastbound | |||
| | 64 | Blacks Creek Road – Kuna | ||||
| Regina | 71 | Mayfield, Orchard | ||||
| Elmore | | 74 | Simco Road | |||
| | 90 |   I-84 BL east to SH-51 / SH-67 – Mountain Home, Bruneau | Eastbound signage | |||
| West Mountain Home | Westbound signage | |||||
| Mountain Home | 95.066– 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 | ||
| Camas | Fairfield |  SH-46 – Gooding, Wendell | ||||
| Blaine | |  SH-75 – Shoshone, Challis | ||||
| Carey |  US 26 / US 93 – Bliss, Twin Falls | Western end of US 26/US 93 concurrency | ||||
| Butte | Arco | US 93 – Challis | Eastern end of US 93 concurrency | |||
| Butte City |  SH-33 – Howe | |||||
| Atomic City | US 26 – Idaho Falls | Eastern end of US 26 concurrency | ||||
| Bingham | No major intersections | |||||
| Bonneville | Idaho 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 | ||||||
| 307 | Lindsay Boulevard | |||||
| 308A | Riverside Drive – City Center | |||||
| 308B | Science Center Drive | Eastbound exit and westbound entrance | ||||
| | 310 | US 20 Bus. – Lewisville | ||||
| Orvin | 311 | Saint Leon Road, 15th East | ||||
| | 313 | Hitt Road, 25th East | ||||
| Ucon | 315 |  SH-43 – Ucon | ||||
| Bonneville–Jefferson county line | | 318 | County Line Road | |||
| Jefferson | Rigby | 320 |  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 | |||||
| Lorenzo | 325 | Menan, Roberts | ||||
| Snake River | Bridge | |||||
| Madison | | 328 | Thornton | |||
| Rexburg | 332 | BYU-Idaho, South Rexburg | ||||
| 333 | SH-33 – Salmon, Rexburg | |||||
| 337 | North Rexburg | |||||
| Sugar City | 338 | Sugar City, Salem | Eastbound exit and westbound entrance | |||
| 339 | To SH-33 east – Driggs, Jackson, Sugar City | Eastern end of Rigby Freeway | ||||
| Fremont | | 344 | South St. Anthony | At-grade intersection; no exit number southbound | ||
| St. Anthony | 346 | 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 Divide | Targhee 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
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References
- ^ a b "Milepoint Log — State Highway System: US 20" (PDF). Idaho Transportation Department. January 25, 2016. Retrieved February 10, 2023.
- ^ 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.
- ^ 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.
- ^ "Drivers ease on down Boise's new roadway". The Idaho Statesman. August 8, 1992. p. 1A. Retrieved February 10, 2023 – via Newspapers.com.
- ^ "Regular Meeting of the Idaho Transportation Board, August 27, 1992" (PDF). Idaho Transportation Department. August 27, 1992. p. 35. Retrieved February 10, 2023.
- ^ "Thornton Interchange opens, U.S. 20 improvements now complete". East Idaho News. November 18, 2016. Retrieved July 16, 2018.