Interstate 115 Montana
Interstate 115, similar to unsigned I-315 at Great Falls to the north, comprises a short freeway spur with a lone interchange. Totaling just 1.197 miles per the Montana Department of Transportation (MDT) 2022 Route Log, I-115 doubles as the westernmost section of the Butte Business Loop for I-15/90. The business routes extend 0.539 miles east along Iron Street to Montana Street north beyond Exit 1.
Source: December 31, 2021 Interstate Route Log and Finders List
I-115 Annual Average Daily Traffic (AADT)
|Location||Vehicles per day|
|I-15/90 to Excelsior Av||4,357|
|Excelsior Av to Washington St||3,303|
|Washington St to Montana St||3.754|
Source: 2021 AADT – MDT’s Interactive Traffic web map
Interstate 115 was part of the proposed urban Interstate numerology for Montana submitted to the American Association of State Highway Officials (AASHO) on July 31, 1958. AASHO approved the proposal on November 10, 1958.
Construction contracts to build Interstate 115 ran concurrent with the those for the I-15/90 overlap through Butte. Contracts to build a 2.6 mile long section of roadway, including all of I-115, and five bridge structures ran simultaneously with completion by September 30, 1964. Contracts to construct the western 2.7 miles of I-15/90 were scheduled to December 31, 1963, and the 5.5 mile section to the east through October 15, 1964.1
The eight mile long stretch of I-15/90 was dedicated on September 24, 1964. Work on the four lane, concrete freeway started in 1960 and cost $8 million.2
East End – Butte, Montana
East North at Iron Street
South West at
West End – Butte, Montana
North East at
Confirming markers for I-115 and Business Loops I-15/90 appear just ahead of the underpass carrying motorists westward along I-15/90. The roadways of the Butte freeway spur stay separate due to the terrain on the initial stretch. Photo by Jeff Royston (05/17/03).
West South at
West End Throwback
- Montana Highway Department. (1963). The Center line: Montana Highway Commission. Helena, MT.
- Montana Highway Department. (September, 1964). The Center line: Montana Highway Commission. Helena, MT.
Page updated June 30, 2022.