Interstate 86 (Western)

Overview

The western Interstate 86 is a rural route linking I-84 east of Twin Falls with I-15 at Pocatello in southeastern Idaho. The freeway parallels the Snake River (Lake Walcott) northeast from Raft River to American Falls. East from there, the route flattens out somewhat adjacent to a Union Pacific Railroad line leading into the Pocatello vicinity.

The eastern Interstate 86 stretches across the Southern Tier of New York from Erie County, Pennsylvania to Binghamton. That route was established in 1999. Prior to that, a separate I-86 ran from Hartford, Connecticut to Sturbridge, Massachusetts from 1969 to 1984. Other split routes include I-76, I-84 and I-88.

I-84/86 Salt Lake City Interchange

Construction started in May 2018 reconfigured the trumpet interchange built in 1960 that joined Interstate 84 and U.S. 30 with the west end of I-86 in Cassia County. The $20 million project realigned the roadways for I-84, eliminating the arc along westbound and shifting the merge with traffic from I-86 to the right. A sweeping loop ramp replaced the shorter radius loop connecting I-86/U.S. 30 west with I-84 east as well. Work wrapped up in Winter 2020.^2,3

I-86/15 Systems Interchange Complex

Construction from mid 2022 to 2025 addresses weaving traffic along Interstate 15 at the east end of I-86 while addressing functionally obsolete bridges within the exchange. A new northbound roadway is being constructed for Interstate 15 within the existing right of way. The former roadway will be rebuilt as a collector distributor roadway extending north from Pocatello Creek Road. Ramps from I-15 north to I-86 west and I-86 east to I-15 north will tie into the c/d roadway, eliminating the left side ramps within the original directional T interchange built in the 1960s.

Parallel U.S. Routes

Interstate 86 follows U.S. 30 (former U.S. 30N) throughout its route in Idaho and has one business loop in American Falls.

History

Interstate 15W was initially to be renumbered as part of newly designated I-84 from Pocatello west to the junction with I-80N; Interstate 86 was the number preferred by Idaho and Utah officials for the I-80N corridor. Instead, the American Association of State Highway and Transportation Officials (AASHTO) conditionally approved the renumbering of I-15W as I-86 and I-80N as I-84 on July 6, 1977. Approval of the renumbering was finalized by November 1977 and sign changes were to be made by January 1, 1978.¹

Route Information

East End – Pocatello, ID
West End – Declo, ID
Branch Routes – 0
Mileage – 62.85
Cities – American Falls, Pocatello
Junctions –

Source: December 31, 2021 Interstate Route Log and Finders List

I-86 Annual Average Daily Traffic (AADT)

Source: Annual Average Daily Travel Application 2018 AADT – IDT

Southeastern Idaho – 1978 Idaho Official Highway Map.

Interstate 15W was renumbered as Interstate 86 three years before sign changes were made along I-80N. Both renumberings were approved by AASHTO in 1977.

Former button copy sign predating the 1980 renumbering of Interstate 15W to I-86 on I-84/U.S. 30 east. Photo by Jeff Royston (07/11/07).

An excerpt from the 1976 Idaho Official Highway Map showing the interchange array along then-Interstate 15W.

Southeast Idaho – 1973 Idaho Official Highway Map.
Interstate 15E was completed from I-80N east to the Power County line and west from Pocatello to Idaho State Highway 37 (Exit 36) outside American Falls. Completion of the freeway directly over laid the remainder of two-lane U.S. 30 along the Snake River.

Photo Guides

Idaho

East End – Pocatello, Idaho

East at

The first sign for Interstate 15 along I-86 east precedes the diverging diamond interchange (DDI) with U.S. 91 (Yellowstone Highway). Photo by Jeff Royston (07/11/07).

Advancing east from U.S. 91, Exit 63 separates in one mile for Interstate 15 north to Idaho Falls and Butte, Montana and south to Ogden and Salt Lake City, Utah. 07/05/16

I-86 spans Hiline Road ahead of the directional T interchange (Exit 63) with Interstate 15. 07/08/16

Traffic partitions at the east end of Interstate 86 with two lanes leading south along I-15 through Pocatello. 07/08/16

North at

Interstate 15 meets the east end of I-86 two miles north of Clark Street and Idaho State University. 07/08/16

Business Loop I-15 returns to I-15 from Downtown Pocatello via Pocatello Creek Road. The freeway proceeds north another mile to Left Exit 72 for I-86 west. 07/08/16

The I-15/86 Systems Interchange project underway from 2022 to 2025 builds a new northbound roadway for I-15 and repurposes the old one as a c/d roadway from Pocatello Creek Road to Interstate 86. 07/08/16

Left Exit 72 departs I-15 north for I-86 west from Chubbuck to Interstate 84 toward Twin Falls, Boise and Portland, Oregon. 07/08/16

South at

A diamond interchange was constructed along Interstate 15 with Northgate Parkway, two miles north of I-86. The exchange opened to traffic following a grand opening event held on the morning of December 6, 2019.⁴ 08/09/16

Interstate 15 advances a half mile south from the Northgate Interchange to I-86 west to Chubbuck, American Falls and I-84 to Twin Falls. 08/09/16

Entering the directional T interchange (Exit 72) with I-86 west on I-15 south. The I-15/86 Systems Interchange project from 2022 to 2025 expands the freeway west to adjacent U.S. 91 along the Chubbuck and Pocatello city line. 08/09/16

East End Throwback

east at

One mile west of Interstate 15 at the previous diamond interchange (Exit 61) with U.S. 91 (Yellowstone Highway) to Chubbuck and Pocatello. Photo by Jeff Royston (07/11/07).

A diagrammatic overhead assembly replaced these ground level signs for Interstate 15 at the Union Pacific Railroad underpass. Photo by Chris Elbert (03/06).

A second lane was added for Exit 63A / I-15 south at the east end of Interstate 86. Blackfoot was removed on the sign replacement for Left Exit 63B. Photo by Chris Elbert (03/06).

North at

One mile south of I-86 on I-15 north at Exit 71 in Pocatello. Photo by Kelly G. Kawamoto (08/00).

Sign replacements at Exit 72 added Chubbuck for I-86 west. Photos by Chris Elbert (03/06).

South at

Former button copy sign posted two miles ahead of Interstate 86 west (Exit 72). Photo by Chris Elbert (03/06).

A half mile north of Exit 72 with I-86 west to American Falls, Twin Falls and Boise. Photo by Chris Elbert (03/06).

Southbound Interstate 15 reaches Exit 72 for I-86 west toward Twin Falls. The succeeding exit serves Downtown Pocatello via Business Loop I-15. Photo by Chris Elbert (03/06).

Western – near Declo, Idaho

West at

Westbound Interstate 86/U.S. 30 converges with I-84 in a remote area of Cassia County in two miles. 08/09/16

2018-20 construction at the Salt Lake Systems Interchange realigned the loop ramp (Exit 1) for Interstate 84 east to Ogden, Utah to improve its geometry. The gore point for Exit 1 was relocated a third of mile eastward. 08/09/16

Westbound I-84 was realigned in 2019 to eliminate the 1960-built overpass along I-86 west at Exit 1. U.S. 30 combines with I-84 west to Heyburn and Burley. 08/09/16

East at

Interstate 84/U.S. 30 proceed east toward I-86 from agricultural areas in the Snake River Valley in rural Cassia County. 08/09/16

Construction underway from May 2018 to Summer 2020 modernized the trumpet interchange with Interstate 86. The exchange was expanded with two lanes for I-84 southeast toward Salt Lake City, Utah and two lanes for I-86/U.S. 30 northeast to American Falls. 08/09/16

Interstate 84 angles southeast to Tremonton, Utah, where it combines with I-15 to Ogden. I-86 parallels the Snake River east to Bannock. 08/09/16

West at

The first guide sign for Interstate 86 and U.S. 30 (Exit 222) appears two miles out along I-84 westbound. 07/05/16

I-86/U.S. 30 east overlap to American Falls and the west side of Pocatello. U.S. 30 west joins I-84 to Heyburn. 07/05/16

Construction underway through Summer 2020 rebuilt the Salt Lake Systems Interchange joining I-84/86. Work reconfigured the westbound roadway of I-84 so that traffic from I-86 merges from the right. 07/05/16

West End Throwback

Previous guide signs for Interstate 86/US 30 east on I-84 west. Photos by Steve Hanudel (05/17/06).

Vintage button copy sign on I-84 east for Interstate 86 and the split with U.S. 30. Photo by Jeff Royston (07/11/07).

The Interstate 84 mainline defaulted onto I-86/U.S. 30 east toward American Falls. Photo by Jeff Royston (07/11/07).

I-84 previously made a TOTSO (turn off to stay on) movement at the trumpet interchange with I-86. Photo by Jeff Royston (07/11/07).

Sources:

“Interstate 80 to become 84.” The Deseret News, August 13, 1977.
I-84/86: Salt Lake City Interchange. ~~https://itdprojects.org/projects/ i-84-86-salt-lake-city-interchange/~~ Idaho Transportation Department Projects.
“ITD planning I-84/86 interchange modernization.” ~~https://www.kmvt.com/content/news/ITD-planning-I-84I-86-interchange-modernization-444085603.html~~ KMVT TV-11 (Twin Falls, ID), September 12, 2017.
I-15 Northgate Interchange. ~~https://itdprojects.org/projects/i-15_northgate/~~ Idaho Transportation Department Projects.

Page updated April 11, 2023.