Interstate 115 Montana
Overview
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 I-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
- Junctions –
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 | 4,145 |
| Excelsior Av to Washington St | 3,190 |
| Washington St to Montana St | 1,898 |
Source: 2018 AADT – MDT’s Interactive Traffic web map
History
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 
– Butte, Montana
East North at Iron Street
A concrete median more in line with a surface arterial separates the roadways of I-115 at Exit 1 for 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.
The speed limit drops to 35 miles per hour as the freeway portion of eastbound Business Loop I-15-90 transitions to Iron Street. Sidewalks and homes line the 0.3 mile stretch to Montana Street. Photo taken 07/05/16.
South West at
Iron Street expands into a four-lane boulevard west from Montana Street. Westbound Business Loop I-15/90 transitions 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.
Shields for I-115 and Business Loops I-15/90 posted at the eastbound entrance ramp from Excelsior Avenue north. A folded diamond interchange joins the two roads. These Business Loop shields were replaced by 2012. Photo taken by Jeff Royston (05/17/03).
West End – Butte, Montana
North East at
Traveling east from Rocker, I-15 north & I-90 east run along a ridge above parallel Silver Bow Creek to the left side 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 (MT 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 & I-15 north branch east to Iron Street in Butte as I-15/90 shifts 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.
Exit 124 departs for I-115 north as the roadways of I-15/90 separate. Photo taken by Steve Hanudel (05/21/06).
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).
West South at
I-15/90 trailblazers appearing beyond the Excelsior Avenue entrance ramp take the place of confirming markers for Business Loop I-15 south & I-90 west along I-115. Photo taken 07/05/16.
A lane drop precedes the Interstate 115 westbound merge with I-15 south & I-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.
West End Throwback
Expansion of I-15 north & I-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).
Sources:
- 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 August 28, 2019.
