Interstate 86 (Idaho)

This article is about the Interstate highway located in southeastern Idaho. For the Interstate highway that runs through New York and Pennsylvania, see Interstate 86 (Pennsylvania–New York). For the former alignment of I-86 east of East Hartford, Connecticut, see Interstate 84 (Pennsylvania–Massachusetts).

Interstate 86 (I-86) is an east–west intrastate Interstate Highway located entirely within the state of Idaho. It runs approximately 63 miles (101 km) from an intersection with I-84 east of Declo in rural Cassia County, to an intersection with I-15 in Chubbuck, just north of Pocatello. The highway is part of the main route from Boise and Twin Falls to Idaho Falls and the upper Snake River region.

Interstate 86
I-86 highlighted in red
Route information
Maintained by ITD
Length	62.85 mi^[1]^[2] (101.15 km)
Existed	1978–present
NHS	Entire route
Major junctions
West end	I-84 / US 30 near Declo
Major intersections	SH-37 in American Falls SH-39 in American Falls US 30 near Pocatello US 91 in Chubbuck
East end	I-15 in Chubbuck
Location
Country	United States
State	Idaho
Counties	Cassia, Power, Bannock
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future Idaho State Highway System Interstate US State
← I-84 → SH-87

I-86 runs through a sparsely populated region along the south side of the Snake River and is mostly concurrent with US Highway 30 (US-30), which it replaced in the 1970s. It passes through American Falls at its midpoint and has a business route that serves the city center. The highway also serves Minidoka National Wildlife Refuge, Massacre Rocks State Park, the Fort Hall Indian Reservation, and Pocatello Regional Airport.

The highway follows a section of the historic Oregon Trail, which was paved and incorporated into US-30N in 1926. Under the original numbering proposal for the Interstate Highway System released in 1957, the highway was supposed to be part of Interstate 82N (I-82N), but it was instead designated as Interstate 15W (I-15W). The first section of the freeway, near American Falls, was completed in 1959. Other sections near Chubbuck and Pocatello were opened in 1968. I-15W was renumbered to I-86 in 1978, shortly before construction of its final section between Raft River and American Falls commenced. The highway was dedicated and opened to traffic on October 11, 1985.

Route description

 

Looking westbound on I-86 at its junction with I-84 near Declo

I-86 begins at an interchange with I-84 and US-30 northeast of Declo. From the interchange, I-84 continues west toward Twin Falls and Boise and southeast toward Salt Lake City, Utah.^[3] I-86 travels east, concurrent with US 30, through rural Cassia County for about 14 miles (23 km) to its first exit at Raft River near a crossing of the river of the same name. From Raft River, I-86 follows the Snake River upstream through Minidoka National Wildlife Refuge and crosses into Power County.^[4]

The freeway continues northeast between the Snake River and the Sublett Range and passes a set of rest areas near Massacre Rocks State Park, one of the state's most popular tourist attractions.^[5] Near Neeley, I-86 passes a wind farm and intersects State Highway 37 (SH-37), which provides a southerly connection to Rockland.^[3][6] A business route of I-86 also terminates at the interchange and continues along the north side of the freeway as it approaches the city of American Falls. I-86 bypasses the city on its east side and intersects the business route and SH-39 near American Falls Airport. From the city, the highway runs along the south side of the American Falls Reservoir and follows a railroad into the Fort Hall Indian Reservation.^[3][4]

 

The penultimate interchange on I-86, at US-91 in Chubbuck

I-86 passes through the northern section of the Fort Hall Reservation, serving exits to Arbon Valley and Pocatello Regional Airport. US-30 leaves the freeway at an interchange located between the eastern boundary of the reservation and the Bannock County line on the Portneuf River.^[3] US-30 continues southeast into Pocatello while I-86 runs through the northern suburb of Chubbuck. The highway intersects US-91 in a diverging diamond interchange, the first to be built in Idaho, on the northeast side of Pine Ridge Mall.^[7] I-86 continues east for approximately one mile (1.6 km) to a directional T interchange with I-15 at the north edge of Pocatello, where it terminates.^[2][4]

At 63 miles (101 km) in length, I-86 is one of the shortest primary Interstate Highways in the contiguous US.^[8] The highway is maintained by the Idaho Transportation Department (ITD), which conducts an annual survey of traffic on certain highway segments that is expressed in terms of annual average daily traffic (AADT), a measure of traffic volume for any average day of the year. The busiest section of I-86 is near its eastern terminus in Chubbuck, carrying an average of 27,158 vehicles. The least-traveled section, near Massacre Rocks, sees only 6,759 vehicles on an average day.^[9]

History

The route of I-86 largely follows the westernmost section of US-30N, which split from US-30S at Burley and continued east into Wyoming.^[10] The corridor was part of the Oregon Trail in the 19th century and was later marked as an auto trail.^[11][12] It was designated as SH-16 in the early 1920s, prior to its incorporation into US-30N in 1926.^[13][14] US-30N was realigned onto a new road near Raft River in 1952, with the intention of upgrading it to a four-lane limited access highway.^[15]

In the original plans for the national expressway and freeway system, which would later become the Interstate Highway System, Pocatello was served by two major highways along US-30N and US-91 and a spur route along US-30N that was removed from later plans.^[16][17] After the Interstate plan was approved by the federal government, present-day I-86 was numbered as part of I-82N^[18] but was eventually designated in 1958 as I-15W.^[19] Construction on the first section of I-15W, a four-lane bypass of American Falls, began in May 1958 and was completed in October 1959.^[20][21] The westernmost stretch of the highway near Raft River was opened in 1963 as part of work on I-80N east of Heyburn.^[22] The Chubbuck section of the freeway was opened to traffic in July 1968 and was followed three months later by an extension to Pocatello Air Terminal 4.6 miles (7.4 km) west of the city.^[23][24] I-15W between American Falls and the airport was opened to traffic in September 1972.^[25]

US-30N was superseded by US-30 in 1972.^[26] In 1973, the American Association of State Highway and Transportation Officials (AASHTO) adopted a new preference for duplicate numbers in lieu of suffixed designations.^[27] As a result, I-15W was redesignated as I-86 in 1978; it was originally submitted as part of I-84 (the successor to I-80N).^[28][29] By 1980, most of the freeway was completed, except for a 21-mile (34 km) section between Raft River and American Falls that was graded and scheduled to be temporarily paved.^[30][31] The final four-lane section was constructed at a cost of $33 million (equivalent to $121 million in 2023^[32]) beginning in 1978 and was dedicated on October 11, 1985.^[33] The highway's construction was delayed by careful rock blasting next to utility lines, historic sites, and native wildlife habitats.^[15]

The interchange with US-91 in Chubbuck was later rebuilt in 2013 as the state's first diverging diamond interchange, which helped reduce the rate of collisions at the interchange.^[7][34] ITD plans to rebuild the interchanges at the western and eastern termini of I-86 to meet modern standards and improve safety. Reconstruction of the western interchange at I-84 near Declo began in May 2018 and was completed in late 2020, replacing the trumpet configuration with a modified Y.^[35][36][37] A major rebuild of the eastern interchange at I-15 in Chubbuck began in August 2022 and is scheduled to be completed in 2025 at a cost of $112 million.^[38] The new design eliminates left-side ramps from I-15 and allows traffic from the Pocatello Creek Road interchange to merge onto either freeway.^[39][40]

Exit list

County	Location	mi^[2]	km	Exit	Destinations	Notes
Cassia	​	0.000	0.000	1	I-84 / US 30 west – Twin Falls, Ogden, Salt Lake	Western terminus; west end of US-30 overlap
	​	14.807	23.830	15	Raft River Area
Power	​	20.590	33.136	21	Coldwater Area
	​	28.100	45.223	28	Massacre Rocks State Park
	​	32.620	52.497	33	Neeley Area
	American Falls	36.123	58.134	36	SH-37 south / I-86 BL east – Rockland, American Falls
		40.110	64.551	40	SH-39 north / I-86 BL west – Aberdeen, American Falls
	​	44.327	71.337	44	Seagull Bay
	​	49.152	79.102	49	Rainbow Road
	​	52.491	84.476	52	Arbon Valley
	​	55.551	89.401	56	Pocatello Regional Airport
	​	58.087	93.482	58	US 30 east – West Pocatello	East end of US-30 overlap
Bannock	Chubbuck	61.268	98.601	61	US 91 (Yellowstone Avenue) – Chubbuck, Pocatello
		62.850	101.147	63	I-15 – Idaho Falls, Salt Lake	Eastern terminus; signed as exits 63A (south) & 63B (north)
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

Business route

Interstate 86 Business
Location	American Falls
Length	4.605 mi^[2] (7.411 km)
Existed	1972–present

Interstate 86 Business (I-86 Bus) is a business route of I-86 that runs between two interchanges in American Falls. It travels northeast from the SH-37 interchange into downtown American Falls on Lincoln Street and Fort Hall Avenue, following the former route of US-30N. The route turns west onto Idaho Street for two blocks and crosses over a railroad before beginning its concurrency with SH-39 around the northwestern side of the city. The highways turn northeast onto Pocatello Avenue, which leads to an interchange with I-86 on the south side of American Falls Airport.^[41]

The business route was originally created in 1972 as I-15W Bus, replacing a section of SH-37 within American Falls.^[42]

Major intersections

The entire route is in American Falls, Power County.

mi^[2]	km	Destinations	Notes
0.000	0.000	I-86 west / US 30 west / SH-37 south – Twin Falls, Rockland	Western terminus
2.942	4.735	SH-39 north – Aberdeen, Blackfoot	West end of SH-39 overlap
4.605	7.411	I-86 east / US 30 east – Pocatello, Idaho Falls	Eastern terminus; east end of SH-39 overlap
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

References

1. Starks, Edward (January 27, 2022). "Table 1: Main Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways". FHWA Route Log and Finder List. Federal Highway Administration. Retrieved September 3, 2022.
2. "Interstate 86 Milepoint Log" (PDF). Idaho Transportation Department. January 25, 2016. Retrieved July 15, 2018.
3. Idaho Official State Highway Map (Map). 1:1,248,000. Idaho Transportation Department. 2016. OCLC 926912754.
4. Google (July 14, 2018). "Interstate 86" (Map). Google Maps. Google. Retrieved July 14, 2018.
5. Johnson, David (May 6, 1990). "Idaho potatoes really are 'famous' in Power County". Lewiston Morning Tribune. Retrieved July 14, 2018.
6. Evensen, Kendra (August 3, 2011). "Wind farm project advances". Idaho State Journal. Pocatello, Idaho.
7. Bryce, Debbie (April 11, 2013). "Diamond In Rough: Most unique overpass in state making drivers, businesses irate". Idaho State Journal. Pocatello, Idaho. Retrieved July 14, 2018.
8. "Part VII - Miscellaneous Interstate Facts". Federal Highway Administration. Retrieved July 15, 2018.
9. "ATR & WIM Data: Interstate 86". Idaho Transportation Department. Retrieved July 15, 2018.
10. H.M. Gousha Company (1956). Shell Highway Map of Wyoming (Map). 1:1,203,840. Shell Oil Company. OCLC 575052172. Retrieved July 15, 2018 – via David Rumsey Historical Map Collection.
11. "Keeping track of the trail". Kansas City Star. May 23, 1993. p. A17. Retrieved September 7, 2021 – via Newspapers.com.
12. Rand McNally Official 1925 Auto Trails Map: Idaho–Montana–Wyoming (Map). 1:1,393,920. Rand McNally. 1925. OCLC 992978006. Retrieved July 16, 2018 – via David Rumsey Historical Map Collection.
13. "Idaho" (Map). Rand McNally Junior Auto Road Map of Idaho. 1927. pp. 76–77. OCLC 921180471. Retrieved July 15, 2018 – via David Rumsey Historical Map Collection.
14. Bureau of Public Roads; American Association of State Highway Officials (November 11, 1926). United States System of Highways Adopted for Uniform Marking by the American Association of State Highway Officials (Map). 1:7,000,000. Washington, DC: United States Geological Survey. OCLC 32889555. Retrieved July 16, 2018 – via Wikimedia Commons.
15. "ITD Vault: Last gap in I-86 dedicated with ceremonies". The Transporter. Idaho Transportation Department. December 4, 2015. Retrieved July 15, 2018.
16. Bureau of Public Roads (September 1955). "Pocatello" (Map). General Location of National System of Interstate Highways Including All Additional Routes at Urban Areas Designated in September 1955. Government Printing Office. p. 19. OCLC 4165975. Retrieved July 16, 2018 – via Wikimedia Commons.
17. Klare, Gene (June 5, 1956). "Federal Road Plan Means East Idaho Super Highways". Idaho State Journal. Pocatello, Idaho. p. 5. Retrieved July 16, 2018 – via Newspapers.com.
18. Official Route Numbering for the National System of Interstate and Defense Highways (JPG) (Map). American Association of State Highway and Transportation Officials. August 14, 1957. Retrieved May 4, 2014.
19. National System of Interstate and Defense Highways, As of June, 1958 (Map). American Automobile Association. June 1958. Retrieved July 16, 2018 – via Library of Congress.
20. "Work Starts Soon on Four-Lane Interstate Highway Near A.F." Idaho State Journal. Pocatello, Idaho. April 21, 1958. p. 1. Retrieved July 15, 2018 – via Newspapers.com.
21. "Interstate Highway Opened Near A.F." Idaho State Journal. Pocatello, Idaho. February 29, 1960. p. B13. Retrieved July 15, 2018 – via Newspapers.com.
22. Rand McNally (1963). Official Highway Map of Idaho (Map). Idaho Transportation Department. OCLC 34000159.
23. "New Interstate to Provide Safer Driving for Motorist". Idaho State Journal. Pocatello, Idaho. July 3, 1968. p. B6. Retrieved July 15, 2018 – via Newspapers.com.
24. "Interstate 'Highway to Sky' Open West of City". Idaho State Journal. Pocatello, Idaho. October 20, 1968. p. A3. Retrieved July 16, 2018 – via Newspapers.com.
25. "Key Links on I-15 Expected Open Soon". Idaho State Journal. Pocatello, Idaho. August 27, 1972. p. A3. Retrieved July 16, 2018 – via Newspapers.com.
26. U.S. Route Numbering Subcommittee (June 20, 1972). "U.S. Route Numbering Subcommittee Agenda Showing Action Taken by the Executive Committee" (Report). Washington, DC: American Association of State Highway Officials. p. 5. Retrieved July 16, 2018 – via Wikisource.
27. (PDF). American Association of State Highway and Transportation Officials. January 2000. Archived from the original (PDF) on November 1, 2006. Retrieved July 16, 2018.
28. Special Committee on U.S. Route Numbering (July 6, 1977). "Route Numbering Committee Agenda" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 1. Retrieved July 16, 2018 – via Wikimedia Commons.
29. "Interstate across Idaho will be I-84". Times-News. Twin Falls, Idaho. Associated Press. September 6, 1979. p. C3. Retrieved July 11, 2018 – via Newspapers.com.
30. Rand McNally. "Idaho" (Map). Rand McNally Road Atlas: United States, Canada, Mexico (1980 ed.). p. 25. LCCN 79-62950. OCLC 80747167. Retrieved July 15, 2018 – via The Internet Archive.
31. "Local highways improved". Times-News. Twin Falls, Idaho. October 4, 1979. p. B2. Retrieved July 15, 2018 – via Newspapers.com.
32. Johnston, Louis; Williamson, Samuel H. (2023). "What Was the U.S. GDP Then?". MeasuringWorth. Retrieved November 30, 2023. United States Gross Domestic Product deflator figures follow the MeasuringWorth series.
33. "Final portion of I-84 done". Times-News. Twin Falls, Idaho. October 5, 1985. p. A3. Retrieved July 15, 2018 – via Newspapers.com.
34. Bryce, Debbie (October 7, 2015). "Officials credit diamond design for fewer crashes at I-86 interchange". Idaho State Journal. Pocatello, Idaho. p. 1. Retrieved February 12, 2023 – via NewsBank.
35. "Substantial Headway Made on Salt Lake Interchange Project East of Burley". Pacific Builder and Engineer. March 9, 2020. Retrieved March 22, 2020.
36. "I-84, I-86 Salt Lake System Interchange Project Status Update – January 2017" (PDF). Idaho Transportation Department. January 2017. Retrieved March 22, 2020.
37. Welch, Laurie (October 19, 2020). "Drivers warned not to avoid detour at Interstate 84-86 work project". Times-News. Twin Falls, Idaho. Retrieved September 13, 2021.
38. Harris, Shelbie (August 1, 2022). "'Historic investment': Gov. Little, state officials highlight aging bridges during 'Flying Y' groundbreaking". Idaho State Journal. Pocatello, Idaho. Retrieved February 12, 2023.
39. "$111.9 million Contract Awarded for Pocatello System Interchange" (Press release). Idaho Transportation Department. May 24, 2022. Retrieved February 12, 2023.
40. O'Connell, John (December 18, 2021). "ITD prepares to bid $100 million overhaul of 'Flying Y' interchange". Idaho State Journal. Pocatello, Idaho. Retrieved February 12, 2023.
41. Google (July 15, 2018). "Interstate 86 Business (American Falls)" (Map). Google Maps. Google. Retrieved July 15, 2018.
42. "Minutes of the Regular Meeting of the Idaho Board of Highway Directors" (PDF). Idaho State Board of Highway Directors. September 12, 1972. p. 212. Retrieved July 15, 2018.

External links

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