Interstate 115 Montana

East End
West End


Butte, Montana Map
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.

Route Information

  • East End – Butte, MT

  • West End – Butte, MT

  • Mileage – 1.19

  • Cities – Butte

  • JunctionsI-15 I-90

Source: December 31, 2018 Interstate Route Log and Finders List

I-115 Annual Average Daily Traffic (AADT)

Location Vehicles per day
I-15/90 to Excelsior Av 4,129
Excelsior Av to Washington St 3,146
Washington St to Montana St 1,999


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

Highway Guides

East End Business I-15 Business I-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).

West End I-15 I-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.


  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.