Local authorities may request route assignment from the Caltrans Transportation System Information Program, and all requests require approval of the executive committee of the American Association of State Highway and Transportation Officials (AASHTO).

It intersects both the westbound and eastbound portions of County Route S6, which in this area is split into one-way roads (which are in turn separated by another street).

This intersection provides access to the end of the Sprinter hybrid rail service.

intersects with El Norte Parkway, a major arterial road, before reconnecting with I-15 at exit 34 near the northern city limits of Escondido.

Though the street itself continues northward well on into Temecula as a frontage road for I-15, its designation as I-15 Bus.

curves to the left onto Promontory Road, while North Main Street's designation is replaced by SR-38.

From there, the routes run beneath a bridge for North 500th Street West and then another bridge for a Union Pacific Railroad line, eventually ending at a folded-diamond interchange with I-15/I-84 at exit 365, while SR-13 continues to run northwest through Corinne and points further north.

begins at I-15 exit 44 along Jensen Road, then turns north and follows State Street to the city of McCammon.

turns west and runs concurrently with US 30 to its northern end at I-15 exit 47.

runs for exactly 1 mile (1.6 km) through Inkom in northern Bannock County.

spans 5.560 miles (8.948 km) through Pocatello in northern Bannock County.

The highways pass by Idaho State University and through downtown Pocatello.

US 30 turns west at Oak Street; the business route and US 91 continue north along Yellowstone Avenue.

has a length of 4.802 miles (7.728 km) through Blackfoot in central Bingham County.

begins at I-15 exit 89 near the northern end of the Fort Hall Indian Reservation and follows US 91 northeast parallel to the Union Pacific Railroad.

In downtown Blackfoot, the routes veer onto Main Street, then I-15 Bus.

The roadway continues beyond the interchange as US 26 and immediately crosses the Snake River.

runs for 3.409 miles (5.486 km) through Idaho Falls in western Bonneville County.

and US 26 follow Yellowstone Avenue northeast parallel to the Union Pacific Railroad into downtown Idaho Falls.

turns northwest onto Broadway Street and runs concurrently with US 20 Bus.

The I-15 Business Loop begins at exit 62 across from a road leading to the Kiwanis International-established Cornell Park, then, after crossing a bridge over an Oregon Short Line Railroad line, curves north along Atlantic Street, briefly crossing another bridge overnight Blacktail Deer Creek.

Moving away from Downtown Dillon, Former US 91 branches off to the northwest, then across from the intersection with Ramshorn Street, the road turns west onto a wrong way concurrency with MT 41.

/ MT 41 climbs a bridge over former US 91 as well as the OSR line and Blacktail Deer Creek all at once, then makes a southbound curve before finally ending at a trumpet interchange at exit 63.

After crossing a bridge over a former Northern Pacific Railroad line, I-15 Bus.

begins to turn northeast and then, at the intersection of North Montana Avenue, becoming Cedar Street running east, eventually ending at I-15 on exit 193 across from the Helena Regional Airport.

terminates at I-15 (concurrent with US 89 and MT 200 through western Great Falls) at each end.

The southernmost 0.83 miles (1.34 km) of the route, from the interchange with I-15 to Fox Farm Road, is designated, but not signed, as Interstate 315.

is at exit 363 on I-15; from there it follows US 2 into the center of Shelby, then follows Montana Highway 67 (Oilfield Road) across the railyard and through the north end of town to its northern terminus at exit 364 on I-15, just south of Shelby Airport.

Interstate 15 Business in Mesquite, Nevada, was also designated as State Route 144.

[3] Route 144, from SR 170 to Hillside Drive, was once US 91, which used to stretch from Sweetgrass, Montana, to Long Beach, California.