Interstate 86 (Western)


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

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

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).


Interstate 15W was initially to be renumbered as part of newly designated Interstate 84 from Pocatello west to the junction with Interstate 80N; I-86 was the number preferred by Idaho and Utah officials for the I-80N corridor. Instead, 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

An excerpt from the 1976 Idaho Official Highway Map showing the interchange array along Interstate 15W (now Interstate 86).

Western Terminus - Interstate 84 - near Declo, Idaho
Perspective from Interstate 84 and U.S. 30 east
On the button copy mileage sign on eastbound Interstate 84 and U.S. 30, the old "15W" was scraped off and replaced with Interstate 86. This means this sign dates to prior to 1980. Photo taken by Jeff Royston (07/11/07).
The two-mile advance sign for the Interstate 84 and Interstate 86/U.S. 30 split is posted on the roadside. Photo taken by Jeff Royston (07/11/07).
Interstate 84/86 and U.S. 30 gantry on Interstate 84/U.S. 30 eastbound at the beginning of Interstate 86. Interstate 84 traffic actually exits the mainline travel lanes, as Interstate 84 transitions to Interstate 86 ahead. Photo taken by Jeff Royston (07/11/07).
A pair of trailblazer shields are posted at the gore point. The left lanes transition onto Interstate 86 and U.S. 30 east, while the right lanes transition onto Interstate 84 east. Photo taken by Jeff Royston (07/11/07).
Perspective from Interstate 84 west
Now traveling northwest on Interstate 84, the first advance signage for Interstate 86 and U.S. 30 (Exit 222) appears two miles prior to the interchange. Photo taken by Steve Hanudel (05/17/06).
Westbound Interstate 84 meets Interstate 86 and U.S. 30 at Exit 222. The right lane exits onto Interstate 86 and U.S. 30 east to American Falls and Pocatello, while the left two lanes continue west toward Twin Falls and Boise. U.S. 30 merges onto westbound Interstate 84. Photo taken by Steve Hanudel (05/17/06).
After traffic from Interstate 86 merges onto Interstate 84, this reassurance shield assembly is posted for westbound Interstate 84 and U.S. 30. Photo taken by Steve Hanudel (05/17/06).
Eastern Terminus - Interstate 15 - Pocatello, Idaho
Perspective from Interstate 86 east
The first advance signage for the end of Interstate 86 appears at this two-mile advance guide sign prior to Exit 61, U.S. 91/Yellowstone Highway and Exit 63, Interstate 15. Photos taken by Jeff Royston (07/11/07) and Chris Elbert (03/06).
Eastbound Interstate 86 reaches Exit 61, U.S. 91/Yellowstone Highway. The next and final interchange serves the connections to Interstate 15 north to Idaho Falls and Butte, Montana and south to Ogden and Salt Lake City, Utah. Photos taken by Jeff Royston (07/11/07) and Chris Elbert (03/06).
Signs for Interstate 15 north and south straddle eastbound Interstate 86. There is no end Interstate 86 shield assembly. Photo taken by Chris Elbert (03/06).
Interstate 15 sign bridge at the eastern end of Interstate 86. Photos taken by Kelly G. Kawamoto (09/00) and Chris Elbert (03/06).
Perspective from Interstate 15 south
Southbound Interstate 15 approaches Exit 72, Interstate 86 (two miles). This is an older, button copy sign, some of which still remain around Idaho. Photo taken by Chris Elbert (03/06).
Southbound Interstate 15 sign bridge approaches its junction with Interstate 86 (former Interstate 15W). Photos taken by Jeff Royston (3/24/02) and Chris Elbert (03/06).
Southbound Interstate 15 reaches Exit 72, Interstate 86 west to American Falls and Twin Falls. The next exit is Exit 71, Business Loop I-15 south into downtown Pocatello. Photo taken by Chris Elbert (03/06).
Now looking down from a nearby overpass north of the Interstate 15 south/Interstate 86 west split, we see that the Exit 71 panel for Business Loop I-15 used to display a tri-color shield for Business Loop I-15. Seeing the 2006 photo in the previous photobox, this error was corrected. Photo taken by Kelly G. Kawamoto (09/00).
Perspective from Interstate 15 north
Interstate 86/15 directional overhead on Interstate 15 north at Exit 71. This section of Interstate 15 was recently widened to three lanes in each direction between Clark Street and the Pocatello Creek Road Exit to handle increasing traffic. Photos taken by Kelly G. Kawamoto (08/00).
The connection from Interstate 15 north to Interstate 86 west is a left exit. Photo taken by Chris Elbert (03/06).
Northbound Interstate 15 reaches Exit 72, Interstate 86 west to American Falls and Interstate 84 west to Twin Falls, Boise, and Portland, Oregon. This also marks the former eastern terminus of Interstate 15W. Photo taken by Chris Elbert (03/06).


  1. "Interstate 80 to become 84." The Deseret News, August 13, 1977.

Page Updated June 9, 2015.

More Info


State Idaho
Mileage 62.85
Cities American Falls, Pocatello
Junctions I-84, I-15
State Pennsylvania
Mileage 6.99
Cities None
Junctions I-90
State New York
Mileage 216.40
Cities Jamestown, Olean, Hornell, Bath, Corning, Elmira
Junctions I-390, I-99
TOTAL 286.24
Source: December 31, 2016 Interstate Route Log and Finders List
I-86 Idaho Annual Average Daily Traffic

County From: To: AADT Composite
Cassia I-84 Exit 15/ Raft River 6,400
Cassia/Power Exit 15/ Raft River Exit 21/ Coldwater 6,400
Power Exit 21/ Coldwater Exit 28/ Massacre Rocks 6,400
Power Exit 28/ Massacre Rocks Exit 33/ Neely 6,400
Power Exit 33/ Neely Exit 36/ West American Falls 6,500
Power Exit 36/ West American Falls Exit 40/ East American Falls 6,300
Power Exit 40/ East American Falls Exit 44/ Seagull Bay 9,900
Power Exit 44/ Seagull Bay Exit 49/ Rainbow Road 10,000
Power Exit 49/ Rainbow Road Exit 52/ Arbon Valley 10,000
Power Exit 52/ Arbon Valley Exit 56 /Air Terminal 11,000
Power Exit 56/ Air Terminal Exit 58/ West Pocatello 12,500
Power/Bannock Exit 58/ West Pocatello Exit 61/ Chubbuck 11,000
Bannock Exit 61/ Chubbuck Exit 63/ I-15 20,500
Source: 2002 Rural Traffic Flow Map (ITD)
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 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.
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.