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 of the route from the interchange with I-15 to Fox Farm Road is designated, but not signed, as Interstate 315 (I-315). 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
thumb|left|[[First Baptist Church (Great Falls, Montana)|First Baptist Church, in the city center on 2nd Avenue, March 2013]]
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. Here, the while I-15 Bus., US 89, MT 3, and MT 200 continue across the Missouri River into downtown Great Falls.