Interstate 15 Business
I-15 Bus. highlighted in red and unsigned I-315 highlighted in blue
Route information
Business route of I-15
Maintained by MDT
Length	5.834 mi[citation needed] (9.389 km)
Existed	1967–present
Major junctions
South end	I-15 / US 89 / MT 3 / MT 200 south of Great Falls
Major intersections	US 89 / MT 3 / MT 200 in Great Falls
North end	I-15 / US 89 / MT 200 in Great Falls
Location
Country	United States
State	Montana
Counties	Cascade
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future Montana Highway System Interstate US State Secondary
← US 312 I-315 → S-315

Interstate 15 Business (I-15 Bus.) is a business loop of Interstate 15 (I-15) in Cascade County, Montana, United States, almost entirely within Great Falls. The route links I-15 (which bypasses downtown Great Falls to the west) with the center of Great Falls. As its business loop designation implies, I-15 Bus. terminates at I-15 (running concurrently with US Highway 89, or US 89, and Montana Highway 200, or MT 200, through western Great Falls) at each end. The southernmost 0.83 miles (1.34 km)^[1] of the route from the interchange with I-15 to Fox Farm Road is designated, but not signed, as Interstate 315 (I-315).^[2] I-315 is the second shortest Interstate in the country; only the unsigned I-878 in New York is shorter; it is also the northernmost auxiliary Interstate of I-15.

Route description

I-15 Bus. begins at I-15 exit 278 in an unincorporated area of Cascade County, a short distance southwest of Great Falls. At the trumpet interchange, US 89 and MT 200 separate from I-15 and merge with I-15 Bus. Additionally, MT 3 begins at the interchange and follows the three routes to the east. Just east of the interchange with I-15, I-15 Bus. intersects 14th Street. The Interstate Highway standard conditions come to an end a short distance to the east at an intersection with Fox Farm Road.^[3] Here, the 0.83-mile (1.34 km)^[1] I-315 (designated along I-15 Bus. from I-15 to Fox Farm Road) comes to an end^[4] while I-15 Bus., US 89, MT 3, and MT 200 continue across the Missouri River into downtown Great Falls.^[3]

Within downtown, the four routes remain concurrent along 10th Avenue South to the parallel one-way couplet of 5th and 6th streets. I-15 Bus. northbound separates from US 89/MT 3/MT 200 at 6th Street, following the street northward through the city to the one-way 2nd Avenue North near the city center. I-15 Bus. turns to the west, following 2nd Avenue North to Park Street, then Park Street south to Central Avenue, where I-15 Bus. northbound rejoins the routing of I-15 Bus. southbound. Between Central Avenue and 10th Avenue South, I-15 Bus. southbound is routed along 1st Avenue North east to 5th Street South, then 5th Street South to 10th Avenue.^[3]

I-15 Bus. follows Central Avenue to the west, crossing the Missouri River once more as it exits downtown. After several intersections with local streets, I-15 Bus. terminates at I-15 exit 280. Central Avenue, however, continues westward from the exit.^[3]

History

Major intersections

The entire route is in Cascade County.

Location	mi	km	Exit	Destinations	Notes
​	0.000	0.000	—	I-15 / US 89 north / MT 200 west / MT 3 begins – Helena, Shelby	Western end of I-315/US 89/MT 3/MT 200 concurrency; I-15 exit 278
Great Falls	0.335	0.539	0	14th Street Southwest	Interchange
	0.828	1.333	—	Fox Farm Road, 6th Street Southwest	Eastern end of I-315 concurrency
	2.341	3.767		US 89 south / MT 3 south / MT 200 east (10th Avenue South) to US 87	Eastern end of US 89/MT 3/MT 200 concurrency; I-15 Bus. becomes 6th Street South (one-way street)
	5.834	9.389		I-15 / US 89 / MT 200 – Helena, Shelby	Northern terminus; I-15 exit 280
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus