The western Interstate 86 is a rural route linking I-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 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 I-76, I-84 and I-88.
I-84/86 Salt Lake City Interchange
Construction started in May 2018 reconfigures the 1960-built trumpet interchange joining Interstate 84 and U.S. 30 with the west end of I-86 in Cassia County. The $20 million project realigns 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 replaces 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 anticipated to start in 2022 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 will be built 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 1960s-built directional T interchange.
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 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, 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