The extant business loops connect to Constantine, Three Rivers, Kalamazoo, Big Rapids, Cadillac, and Manton.
The highway passes a mobile home park and a couple of businesses before veering northwesterly on Washington Street through a residential neighborhood on the south side of Constantine.
The loop runs parallel to the banks of the river as the highway exits the northern side of the village.
[3][4] The Michigan Department of Transportation (MDOT) has been studying a freeway upgrade for US 131 through St. Joseph County for several years.
In late 2005, MDOT decided not to pursue an upgrade of the highway, but rescinded that decision in April 2006[5] under political pressure in the state.
On the east side of the river, the business loop turns north-northwesterly onto Main Street, separating from M-60 at an intersection that also features M-86.
US 131 (Main Street) passes several more businesses and turns due north through a residential area.
[12][13] The Three Rivers Bypass opened in the middle of 1953, and the former route of the highway through downtown was redesignated as the business loop at that time.
US 131 followed M-43 eastward from the end of the freeway into the downtown area to reconnect to its original routing along Westnedge and Park.
[14][15] Later in 1965, Kalamazoo and Michikal avenues were transferred to state jurisdiction to set up the one-way pairing east–west through downtown.
Only northbound traffic on US 131 could directly access the business loop at this interchange, running northward on a long ramp that connects to Ottawa Avenue at an intersection with Cherry Street.
US 131 followed Ottawa Avenue northward between parking lots, and after one block, it turned eastward onto Oakes Street immediately south of the Van Andel Arena.
Division Street here runs at the base of Belknap Hill through an area of the city dominated by industrial-type properties.
North of an intersection with Coldbrook Street, the business loop switched to Plainfield Avenue and turned northeasterly.
After the change, the former mainline through downtown on Division Street and Plainfield Avenue was redesignated Bus.
[44] Jurisdiction was transferred in December, and the American Association of State Highway and Transportation Officials approved the removal of the designation in May 2018.
At this interchange, M-20 leaves the freeway to run concurrently eastward with the business loop along the four-lane Perry Street into town.
US 131/M-20 passes several commercial properties on the western edge of Big Rapids before crossing the city limits.
US 131/M-20 turns northward toward downtown Big Rapids, passing the northern end of the FSU campus.
At the intersection with Maple Street immediately west of downtown, M-20 turns easterly and separates from Bus.
North of the downtown area, State Street ends, and the business loop follows Northland Drive parallel to the Muskegon River.
On the northern edge of the city, the highway passes Roben–Hood Airport before exiting town as a two-lane road.
Running in a rural area in Big Rapids Township, the business loop turns westward onto 19 Mile Road.
At the time, 19 Mile Road between the freeway Northland Drive was used by the mainline to connect to its pre-existing routing north of Big Rapids to Reed City.
US 131 was extended over the 19 Mile Road portion of US 131 to connect with its parent route at exit 142 northwest of Big Rapids.
North of the cemetery, Mitchell Street descends a hill through a residential neighborhood south of downtown.
North of downtown, Mitchell Street turns more northerly and passes the Wexford County Civic Center.
The business loop starts at an interchange with US 131 and M-42 east of downtown Manton in Cedar Creek Township.
North of Manton, the turn lane is eliminated, and the surrounding landscapes are dominated by farm fields broken by intermittent patches of forest.
As the business loop approaches northern end of the freeway mainline in Liberty Township, it curves northeasterly to meet it at an at-grade intersection.