Interstate 86 (Idaho)
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Interstate 86 (I-86) is an east–west intrastate
Interstate Highway The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Hi ...
located entirely within the state of
Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...
. It runs approximately from an intersection with
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts), passing through New York and Connecticut {{road disambiguation ...
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 Boise ( ) is the capital and most populous city of the U.S. state of Idaho. As of the 2020 census, there were 235,685 people residing in the city. Located on the Boise River in southwestern Idaho, it is east of the Oregon border and nor ...
and Twin Falls to
Idaho Falls Idaho Falls is the List of cities in Idaho, fourth most populous city in Idaho and the county seat of Bonneville County, Idaho, Bonneville County. It is the state's most populous city outside the Boise metropolitan area. As of the 2020 United St ...
and the upper
Snake River The Snake River is a major river in the interior Pacific Northwest region of the United States. About long, it is the largest tributary of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. Begin ...
region. 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 The American Falls is the second largest of the three waterfalls that together are known as Niagara Falls on the Niagara River along the Canada–United States border. Unlike the much larger Horseshoe Falls, of which approximately 90% is in On ...
at its midpoint and has a
business route A business route (or business loop, business spur, or city route) in the United States is a short special route that branches off a parent numbered highway at its beginning, continues through the central business district of a nearby city or to ...
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 The Oregon Trail was a east–west, large-wheeled wagon route and Westward Expansion Trails, emigrant trail in North America that connected the Missouri River to valleys in Oregon Territory. The eastern part of the Oregon Trail crossed what ...
, 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

I-86 begins at an interchange with
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts), passing through New York and Connecticut {{road disambiguation ...
and US-30 northeast of Declo. From the interchange, I-84 continues west toward Twin Falls and
Boise Boise ( ) is the capital and most populous city of the U.S. state of Idaho. As of the 2020 census, there were 235,685 people residing in the city. Located on the Boise River in southwestern Idaho, it is east of the Oregon border and nor ...
and southeast toward
Salt Lake City, Utah Salt Lake City, often shortened to Salt Lake or SLC, is the List of capitals in the United States, capital and List of cities and towns in Utah, most populous city of the U.S. state of Utah. It is the county seat of Salt Lake County, Utah, Salt ...
. I-86 travels east, concurrent with US 30, through rural Cassia County for about 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 The Snake River is a major river in the interior Pacific Northwest region of the United States. About long, it is the largest tributary of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. Begin ...
upstream through Minidoka National Wildlife Refuge and crosses into Power County. The freeway continues northeast between the Snake River and the Sublett Range and passes a set of
rest area A rest area is a public facility located next to a large thoroughfare such as a motorway, Limited-access road, expressway, or highway, at which drivers and passengers can rest, eat, or refuel without exiting onto secondary roads. Other names ...
s near Massacre Rocks State Park, one of the state's most popular tourist attractions. Near Neeley, I-86 passes a
wind farm A wind farm, also called a wind park or wind power plant, is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an exten ...
and intersects State Highway 37 (SH-37), which provides a southerly connection to Rockland. A
business route A business route (or business loop, business spur, or city route) in the United States is a short special route that branches off a parent numbered highway at its beginning, continues through the central business district of a nearby city or to ...
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 The American Falls is the second largest of the three waterfalls that together are known as Niagara Falls on the Niagara River along the Canada–United States border. Unlike the much larger Horseshoe Falls, of which approximately 90% is in On ...
. 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. 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. 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 A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the inte ...
, the first to be built in Idaho, on the northeast side of Pine Ridge Mall. I-86 continues east for approximately to a directional T interchange with I-15 at the north edge of Pocatello, where it terminates. At in length, I-86 is one of the shortest primary Interstate Highways in the contiguous US. The highway is maintained by the
Idaho Transportation Department The Idaho Transportation Department (ITD) is the state of Idaho Government agency, governmental organization responsible for state transportation infrastructure. This includes ongoing Maintenance, repair and operations, operations and maintenanc ...
(ITD), which conducts an annual survey of traffic on certain highway segments that is expressed in terms of
annual average daily traffic Annual average daily traffic (AADT) is a measure used primarily in transportation planning, transportation engineering and retail location selection. Traditionally, it is the total volume of vehicle traffic of a highway or road for a year divided ...
(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.


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 Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...
. The corridor was part of the
Oregon Trail The Oregon Trail was a east–west, large-wheeled wagon route and Westward Expansion Trails, emigrant trail in North America that connected the Missouri River to valleys in Oregon Territory. The eastern part of the Oregon Trail crossed what ...
in the 19th century and was later marked as an
auto trail The system of auto trails was an informal network of marked routes that existed in the United States and Canada in the early part of the 20th century. Marked with colored bands on utility poles, the trails were intended to help travellers in t ...
. It was designated as SH-16 in the early 1920s, prior to its incorporation into US-30N in 1926. 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. 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 A spur route is a short road forming a branch from a longer, more important road such as a freeway, Interstate Highway, or motorway. A Bypass route, bypass or beltway is not considered a spur route as it typically reconnects with another or the ...
along US-30N that was removed from later plans. After the Interstate plan was approved by the federal government, present-day I-86 was numbered as part of I-82N but was eventually designated in 1958 as I-15W. 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. The westernmost stretch of the highway near Raft River was opened in 1963 as part of work on I-80N east of Heyburn. 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 west of the city. I-15W between American Falls and the airport was opened to traffic in September 1972. US-30N was superseded by US-30 in 1972. In 1973, the
American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway A highway is any public or private road ...
(AASHTO) adopted a new preference for duplicate numbers in lieu of suffixed designations. As a result, I-15W was redesignated as I-86 in 1978; it was originally submitted as part of
I-84 Interstate 84 may refer to: * Interstate 84 (Oregon–Utah), passing through Idaho, formerly known as Interstate 80N * Interstate 84 (Pennsylvania–Massachusetts), passing through New York and Connecticut {{road disambiguation ...
(the successor to I-80N). By 1980, most of the freeway was completed, except for a section between Raft River and American Falls that was graded and scheduled to be temporarily paved. The final four-lane section was constructed at a cost of $33 million (equivalent to $ in ) beginning in 1978 and was dedicated on October 11, 1985. The highway's construction was delayed by careful rock blasting next to utility lines, historic sites, and native wildlife habitats. The interchange with US-91 in Chubbuck was later rebuilt in 2013 as the state's first
diverging diamond interchange A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the inte ...
, which helped reduce the rate of collisions at the interchange. 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 The trumpet is a brass instrument commonly used in classical and jazz musical ensemble, ensembles. The trumpet group ranges from the piccolo trumpet—with the highest Register (music), register in the brass family—to the bass trumpet, pitche ...
configuration with a modified Y. 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. The new design eliminates left-side ramps from I-15 and allows traffic from the Pocatello Creek Road interchange to merge onto either freeway.


Exit list


Business route

Interstate 86 Business (I-86 Bus) is a business route of I-86 that runs between two interchanges in
American Falls The American Falls is the second largest of the three waterfalls that together are known as Niagara Falls on the Niagara River along the Canada–United States border. Unlike the much larger Horseshoe Falls, of which approximately 90% is in On ...
. 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. The business route was originally created in 1972 as I-15W Bus, replacing a section of SH-37 within American Falls.


Major intersections


References


External links

* {{DEFAULTSORT:Interstate 86 (West) Interstate 15 86 west 86 Transportation in Bannock County, Idaho Transportation in Cassia County, Idaho Transportation in Power County, Idaho 086