Interstate 315 Montana
Overview
Interstate 315 spurs east from I-15 by Great Falls Market Place shopping center to Country Club Boulevard at 6th Street SW. Measuring just 0.824 miles in length per the 2022 Montana Department of Transportation (MDT) Route log, I-315 is only slightly longer than the shortest Interstate highway, unsigned Interstate 878 near John F. Kennedy International Airport (JFK) in New York City.
Signs for Exit 278 along Interstate 15 reference Business Loop I-15, U.S. 89 and MT 200. I-315 is omitted due to the number of overlapped routes. MT 3 is also routed along the freeway, but equally unsigned.
The Great Falls Business Loop for Interstate 15 loops east via U.S. 89 and MT 200 along Country Club Boulevard and 10th Avenue S to 5th Street south and 6th Street north. The I-315 portion passes over both 14th Street SW and a BNSF Railroad. An 11 block long couplet takes the business route north 0.8 miles from U.S. 89/MT 3-200 (10th Avenue S) to 1st Avenue N and the central business district. 1st Avenue west across the Missouri River to Central Avenue returns Business Loop I-15 solo to I-15 at Exit 280.
Montana Highway 3 begins alongside Interstate 315 from I-15. The state highway connects Great Falls with Billings, and it is cosigned with U.S. 89, MT 200, U.S. 87, U.S. 191 and U.S. 12. The only section of MT 3 that is not cosigned with another route is the segment between U.S. 12 at Lavina and Interstate 90 at Exit 450 in Billings. The extended MT 3 was commissioned around 2000; originally it only traveled between Lavina and Billings.
History
Interstate 315 was one of two routes in the proposed urban Interstate numerology submitted to the American Association of State Highway Officials (AASHO) by the State of Montana Highway Commission on July 31, 1958. I-315 along with I-115 at Butte were both approved by AASHO on November 10, 1958.
A contract to build a 0.6 mile long section of Interstate 315 was completed by September 15, 1967.1 The lone interchange (Exit 0) at 14th Street SW was added in 1995.
Route Information
East End – Great Falls, MT
West End – Great Falls, MT
Mileage – 0.83
Cities – Great Falls
- Junctions –
Source: December 31, 2021 Interstate Route Log and Finders List
I-315 Annual Average Daily Traffic (AADT)
| Location | Vehicles per day |
|---|---|
| I-15 to Exit 0 | 12,366 |
| Exit 0 to Fox Farm Rd | 23,173 |
| East of Fox Farm Rd | 26,716 |
Source: 2021 AADT – MDT’s Interactive Traffic web map
Business Loop I-15 follows the couplet of 5th and 6th Street between U.S. 89 and 1st Avenue.
Highway Guides
East End 
at Fox Farm Road – Great Falls, Montana
East North South at 6th Street SW / Fox Farm Rd
The speed limit reduces to 45 miles per hour as the freeway along I-315 transitions to Country Club Boulevard. Business Loop I-15, U.S. 89/MT 3-200 advance another 1.8 miles to 6th Street S in Great Falls. 07/07/16
6th Street SW angles northeast across the Sun River to the Jewel Addition area of Great Falls. Fox Farm Road extends south from the signalized intersection to Montana Addition and other subdivisions. A controlled access section of Business Loop I-15 ensues from the traffic light to 4th Street S. 07/07/16
West South North
Country Club Road parallels the Sun River from the Missouri River bridge west to the traffic light with 6th Street SW north and Fox Farm Road west. I-315 begins a short distance after this intersection. 07/07/16
I-315 begins at the folded diamond interchange (Exit 0) with 14th Street SW. The concrete median here is similar to the one at the westbound beginning of I-115. 07/07/16
The last confirming markers for both Business Loop I-15 south and MT 3 precede the off-ramp (Exit 0) to 14th Street SW. Great Falls Market Place, a big box retail center, lies just to the south. Photo by Jeff Royston (07/17/07).
West End – Great Falls, Montana
West South North
Traffic partitions to Interstate 15 north and south a short distance west of the 14th Street SW entrance ramp. U.S. 89 north / MT 200 west combine with I-15 north for an 11 mile long overlap to Vaughn. Shelby, located at the cross roads with U.S. 2, is 85 miles to the northwest. 07/07/16
I-315/MT 3 west end as the freeway mainline defaults onto I-15 south to Great Falls International Airport (GTF) and the capital city of Helena. 07/07/16
This set of signs for Interstate 15, U.S. 89 and MT 200 at the south end of Business Loop I-15 was replaced by 2015. Photo by Jeff Royston (07/17/07).
North at
Leading away from Great Falls International Airport (GTF), Interstate 15 advances to the trumpet interchange (Exit 278) with unsigned I-315, Business Loop I-15 north, U.S. 89 south and MT 3-200 east. 07/07/16
I-15 north reaches the off-ramp for I-315. Beyond the Missouri River bridge and viaduct, U.S. 89/MT 2-300 transition to 10th Avenue. U.S. 87 combines with the three at 15th Street southeast to Malmstrom A.F.B. and Belt. 07/07/16
South East at
Interstate 15/U.S. 89-MT 200 turn south from the split with Business Loop I-15 to cross the Sun River and next meet unsigned I-315 at Exit 278. MT 200 is part of multi state route extending east from Idaho to Minnesota across the northern tier of the United States roughly parallel to U.S. 2. 07/07/16
A trumpet interchange (Exit 278) returns Business Loop I-15 south from 10th Avenue S and Country Club Boulevard to I-15 in one quarter mile. Although unsigned here, MT 3 also begins. The state highway was designated to connect Great Falls with Billings on a consistently numbered route. 07/07/16
Exit 278 takes U.S. 89 south / MT 200 east from I-15 to combine with Business Loop I-15 eastward to 10th Avenue S. U.S. 89 travels south from the Canadian border north of Babb, Montana to Flagstaff, Arizona; it previously extended south to Mexico at Nogales, Arizona. 07/07/16
East North South
Traffic from I-15 north and south combines just ahead of this shield assembly with the first marker for MT 3. A loop ramp (Exit 0) quickly follows for 14th Street SW. Photo by James Horton (03/29/03).
Sources:
- Montana Highway Department. (1965). The Center line: Montana Highway Commission. Helena, MT.
Page updated August 28, 2019.
