U.S. Route 20 in Idaho

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

U.S. Highway 20
US 20 highlighted in red
Route information
Maintained by ITD
Length	411 mi[1] (661 km)
Existed	1940[2]–present
Major junctions
West end	US 20 / US 26 at the Oregon state line
	US 95 in Parma I-84 in Caldwell I-84 in Garden City I-84 / US 26 in Mountain Home US 26 in Carey US 26 / US 93 in Atomic City I-15 in Idaho Falls
East end	US 20 at the Montana state line
Location
Counties	Payette, Canyon, Ada, Elmore, Camas, Blaine, Butte, Bingham, Bonneville, Jefferson, Madison, Fremont
Highway system
United States Numbered Highway System List Special Divided State Highways in Idaho Interstate U.S. State ← SH-19 → SH-21

Route description

I-15/US-20 Jct. in Idaho Falls, ID

US 20 crosses into Idaho northwest of Parma, running concurrently with US 26 and joins US 95 through Parma. US 20/US 26 leaves US 95 southeast of Parma and runs to Caldwell where US 20/US 26 joins with I-84 and US 30 for a short time. These four highways parallel each other (on two roadways) to Boise where US 20/US 26 runs through downtown before joining with I-84 and US 30 again to Mountain Home, where it departs at exit 95 to head east, past Rattlesnake Station, Anderson Ranch Dam road, and cresting at Cat Creek summit at 5,527 feet (1,685 m) above mean sea level. It continues into and across Camas County through Fairfield to Timmerman Junction, the intersection in Blaine County with State Highway 75, the route to Sun Valley, Galena Summit, and Stanley. US 20 continues east through Picabo and Carey, joined with US 26 and US 93, to Craters of the Moon 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 the Idaho National Laboratory, where the highways split just west of Atomic City; US 26 heads 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.[2]

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.[3]

Junction list

County	Location	mi[4]	km	Exit	Destinations	Notes
Snake River		0.000	0.000		US 20 / 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	West 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	East 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 Rd.) and 59B (Memory Rd.) 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 west / 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 junctions
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	Signalized interchange; eastern end of I-15 concurrency; I-15 exit 119; access to airport via Grandview Avenue
				West end of Rigby Freeway
				—	Lindsay Boulevard
				—	Riverside Drive – City Center
				—	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 US 20 Bus. to SH-48 – Rigby	Eastbound signage 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	East 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       Concurrency terminus       Incomplete access       Route transition

References

1. Google (February 29, 2016). "Snake River to Yellowstone National Park" (Map). Google Maps. Google. Retrieved February 29, 2016.
2. 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. "Thornton Interchange opens, U.S. 20 improvements now complete". East Idaho News. November 18, 2016. Retrieved July 16, 2018.
4. "Milepoint Log — State Highway System" (PDF). Idaho Transportation Department. Retrieved April 15, 2016.

External links