Interstate 115 Montana

Situated at 5,538 feet above sea level, Butte is home to nearly 35,000 residents. The city and Silver Bow County form a consolidated government. I-115 provides a gateway toward the city center from the west.


Interstate 115, similar to unsigned I-315 at Great Falls to the north, comprises a short freeway spur with a lone interchange. Totaling just 1.194 miles per the MDT 2013 Route Log, I-115 doubles as the westernmost section of the Butte Business Loop for Interstates 15 & 90. The business routes extend east along Iron Street to Montana Street north beyond Exit 1.


Construction contracts to build Interstate 115 were run concurrent with the those for the I-15 & 90 overlap through Butte. Contracts to build a 2.6-mile section of roadway, including all of I-115, and five bridge structures were run 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 stretch of Interstates 15 & 90 was dedicated on September 24, 1964. Work on the four-lane concrete freeway started in 1960 and cost $8 million.2

Interstate 115 Guide

Western Terminus - Interstates 15 & 90 - Butte, Montana
Perspective from Interstates 15 north & 90 east
Traveling east from Rocker, I-15 north & 90 east run along a ridge above parallel Silver Bow Creek to the left-hand ramp (Exit 124) for Interstate 115 east. Photo taken 07/05/16.
A second diagrammatic sign precedes the wye interchange (Exit 124) with I-115 east. The local exits of Montana Street and Harrison Avenue (Montana 2) appear in place of Billings and Bozeman for the continuation of I-15 & 90 east. Photo taken 07/05/16.
Interstate 115-Business Loop I-90 east & 15 north begin and stem east to Iron Street in Butte as I-15 & 90 shift southeast to cross Silver Bow Creek ahead of Williamsburg. The business loops return to the freeway via Harrison Avenue south at Exit 127. Photo taken 07/05/16.
A bubble shield directs motorists to I-115 north as the roadways of I-15 & 90 separate. Photo taken by Steve Hanudel (05/21/06).
Historic Perspective from Interstates 15 north & 90 east
Expansion of Interstates 15 north & 90 east from the Rocker interchange included the replacement of the initial sign bridge for I-115. The added eastbound lane ends a short distance ahead. Photo taken by Steve Hanudel (05/21/06).
The subsequent diagrammatic sign for Exit 124 and I-115 was carbon copied by 2015. Photo taken by Jeff Royston (05/17/03).
Perspective from Interstate 115 east
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 taken by Jeff Royston (05/17/03).
Perspective from Interstate 115 west
Trailblazers for I-15 & 90 take the place of confirming markers for Business Loop I-15 south & 90 west along I-115. This stands west of the Excelsior Avenue on-ramp. Photo taken 07/05/16.
A lane drop precedes the Interstate 115 westbound merge with I-15 south & 90 west. Photo taken 07/05/16.
Traffic from i-115 west lowers onto I-15 & 90, 1.5 miles ahead of the Rocker interchange. The forthcoming exit is home to a pair of truck stops. Photo taken 07/05/16.
Eastern Terminus - Business Loop I-15 & 90 - Butte, Montana
Perspective from Interstate 115 east
A concrete median more in line with a surface arterial appears as eastbound motorists along I-115 reach Exit 1 to Excelsior Avenue. Photo taken 07/05/16.
The second and final reassurance marker for Interstate 115 stands east of the Excelsior Avenue underpass. Photo taken 07/05/16.
Speed limits drop to 35 miles per hour as the freeway portion of Business Loop I-15 north & 90 east transitions to Iron Street. Sidewalks and homes line the 0.3 mile stretch to Montana Street. Photo taken 07/05/16.
Perspective from Interstate 115 west
Iron Street expands into a four-lane boulevard west from Montana Street. Business Loops I-15 south & 90 west transition into I-115 beyond the end of on-street parking at Clark Street. The first shield for Interstate 115 follows. Photo taken 07/07/16.
Perspective from the Excelsior Avenue
Shields for I-115 and Business Loop I-15 & 90 posted at the eastbound on-ramp from Excelsior Avenue north. A folded diamond interchange joins the two roads.
The Business Loop shields here were replaced by 2012. Photo taken by Jeff Royston (05/17/03).


  1. Montana Highway Department. (1963). The Center line: Montana Highway Commission. Helena, MT.
  2. Montana Highway Department. (September, 1964). The Center line: Montana Highway Commission. Helena, MT.

Page Updated July 15, 2016.