Falls. 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, 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 (ITD), which conducts an annual survey of traffic on certain highway segments that is expressed in terms of annual average daily traffic (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. The corridor was part of the Oregon Trail in the 19th century and was later marked as an auto trail. 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 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