It starts at a semi-trumpet interchange at exit 106 on I-90 at U.S. Route 97 then passes through a roundabout and continues along West University Way entering downtown.

Then, the route becomes Canyon Drive after intersecting West Mountain View Avenue, and heads southeast to its southern terminus at a folded-diamond interchange with I-90/US 97 at exit 109.

[1] Historic US 10 continues east of the Ritzville city line for another 9 miles (15 km) before terminating at Interstate 90.

The route began near Spokane International Airport at exit 276, a parclo interchange on Grove Road where it briefly ran northwest, then turned northeastbound along South Geiger Boulevard.

From its western terminus at exit 285, the route travels eastbound along Appleway Boulevard and westbound Sprague Avenue.

The business route continues northeast onto Appleway Avenue and turns north onto Barker Road in Greenacres, terminating at exit 293.

[6] Sprague Avenue had previously been part of U.S. Route 10, the transcontinental predecessor to I-90, and reached its present width of 62 feet (19 m) in 1949.

The highway moved to the present I-90 route after the freeway and Veterans Memorial Centennial Bridge was completed in the early 1990s.

The business loop continues southeast past North Idaho College turns east on Sherman Avenue near a city park, beach, marina, and the Lake Coeur d'Alene Resort.

The highway moved to the present I-90 route after the freeway and Veterans Memorial Centennial Bridge was completed in the early 1990s.

It ran from a diamond interchange at exit 49 north along Bunker Avenue until the intersection with West Cameron Avenue (Old Highway 10), where it turned south onto Division Street and joined its parent route at the eastbound on-ramp for Exit 51 (a diamond interchange with no westbound on-ramp), finally coming to an end.

After the intersection of 3rd Avenue curves from northeast to east as it runs over a second bridge over the South Fork of the Coeur d'Alene River.

As it crosses over a railroad bridge, it immediately leaves US 93 at an interchange with West Broadway Street, and turns southeast.

BL-90 briefly parallels the south side of the former Northern Pacific Railway line but turns away at the intersection with Railroad Street West, still remaining in a relative southeast trajectory.

Between Hawthorne and McCormick Streets, it runs directly along the north bank of the Clark Fork River before reaching the Heart of Missoula.

Utah Avenue ends at East Front Street across from a former Northern Pacific Railroad depot and BL-15/90 makes a left turn there.

Then after the intersection with Bramble Street, US 191 continues northeast, while BL-90 curves southeast onto Big Timber Loop Road (Old U.S. 10).

Winding northeast around a former segment of the road still used by local farmers, BL-90 finally turns south and ends at a diamond interchange with I-90 at exit 370.

It runs from a diamond interchange at exit 495 on I-90 at North Crawford Avenue in a two block concurrency with Montana Highway 47 then makes a left turn onto 14th Street West, only to curve south again onto Center Street until it reaches "Old US 87," and makes another left torn to go east.

BL 90 ends at a full diamond interchange at exit 58 on I-90, but US 16 continues to run east towards Ucross.

The routes curve to towards the northeast passing over Sundance Creek directly east of WY 116, and later run beneath I-90 again, but with no interchange.

Two blocks after WY 585, the routes intersect with Eighth Street, whose southeast corner contains Sundance High School followed by Washington Park, which includes the Crook County Fairgrounds.

A "Port of Entry" can be found at the east end of the Business Loop on the south side of exit 189, along with a small rest area.

Less than one block after the interchange, BL 90 veers off to the right onto South Boulevard (former US 14 and 16), running southeast, while Airport Road turns into West Fourth Avenue after a landing strip and heads towards the famous Wall Drug Store and other local tourist attractions.

South Boulevard passes a local high school before becoming a divided highway and crossing the former Chicago and Northwestern Railway line.

Just as SD 248 starts to curve to the east, BL 90 leaves the overlap turning north onto South Creek Road and finally terminates at a diamond interchange with I-90 at exit 152.

It runs from a diamond interchange at exit 191, then follows Fifth Avenue (South Dakota Highway 248), passing by sites such as the Pioneer Auto Museum.

The route began at a diamond interchange at exit 212, at the east end of the overlap with US 83, and northern terminus of South Dakota Highway 53.

It runs from a diamond interchange at exit 330 and includes a concurrency with South Dakota Highway 37 along Ohlman Street, then turns right onto West Havens Avenue.

The surroundings become slightly more industrial, as it passes the Martin County Fair just before crossing a former Milwaukee Road railroad line, and then makes a left turn at CSAH 26.