Interstate 86 west(I-86) is an intrastate Interstate Highway, located entirely within the state of Idaho. It runs 63 miles (101.4 kilomters) from an intersection with Interstate 84 located approximately 7 miles (11.3 kilometers) east of Declo in rural Cassia County, to an intersection with Interstate 15 at Pocatello. Interstate 86 connects the major eastern Idaho cities of Pocatello and Idaho Falls with the state's Magic Valley region.
Interstate 86 was originally numbered as Interstate 15W in the 1970s however AASHTO decided it was better to have duplicate numbers in different parts of the country instead of having suffixes. (See Interstate 86 (east).) There was also an Interstate 15E in California at the time.
Besides being somewhat short, the area Interstate 86 passes through is very desolate. Pocatello and American Falls are the only incorporated settlements located on the highway. Between American Falls and Pocatello I-86 passes through a portion of Fort Hall Indian Reservation.
I-86 east begins at Interstate 90 in a relatively flat area of northwestern Pennsylvania, and crosses into New York, heading towards Chautauqua Lake.