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US HIGHWAY 20 |
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Length in Idaho |
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Length nationally |
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Termini in Idaho |
1940-present |
Nyssa, OR |
Targhee Pass |
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MULTIPLEXES |
Nyssa, OR |
Mountain Home |
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(north of Parma) |
(south of Parma) |
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(west of Caldwell) |
Caldwell |
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(west of Caldwell) |
Caldwell |
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Boise |
Mountain Home |
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Boise |
Mountain Home |
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Carey |
(west of Atomic City) |
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Carey |
Arco |
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Idaho Falls |
Idaho Falls |
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BANNERED ROUTES |
US 20 Business |
Idaho Falls |
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Temporary
US 20 |
Mountain Home |
Carey |
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NOTES |
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US 20 is the longest or second-longest highway in the United States, depending on whether the length of the implied route through Yellowstone Park is included (some consider it two separate highways). US 20 is a controlled-access highway for some of its length, more than any other US highway in Idaho (not counting those multiplexed with Interstates); US 20/26 is a freeway for about 2 miles in Boise, and the section from Idaho Falls to St Anthony is being converted to a divided freeway. US 20 is multiplexed with US 26 in all of western Idaho as well as in the Arco area (the highways are also multiplexed from Vale to Nyssa, OR, and from Shoshoni to Orin, WY). US 20 was originally planned through Idaho in 1926 along roughly its present route, but the section between Mountain Home and Carey was a poor dirt road in some places, and nonexistent in others! Therefore, its western terminus was at Yellowstone Park. However, in 1940, apparently ITD got impatient and signed US 20 through Idaho. Where the planned route was not completed (through Fairfield), US 26 was signed as Temporary US 20 (some maps show US 20T). The planned route through Fairfield was signed as Idaho 68 until it was at US highway standards (some alternate routings were used). |
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